Table of Contents

Volume 3, Issue 9

  September 2008

  Pages 615 - 757

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 Issue Catalogue (MARC XML)

SHORT COMMUNICATION

Open Access Article

Small interfering peptides as a novel way of transcriptional control

Ju Yun, Sang-Gyu Kim, Shinyoung Hong and Chung-Mo Park
Pages 615 - 617
http://dx.doi.org/10.4161/psb.3.9.6225
Abstract | PDF

Transcription factors are key components of transcriptional regulatory networks governing virtually all aspects of plant growth and developmental processes. Their activities are regulated at various steps, including gene transcription, posttranscriptional mRNA metabolism, posttranslational modifications, nucleocytoplasmic transport, and controlled proteolytic cleavage of membrane-anchored, dormant forms. Dynamic protein dimerization also plays a critical role in this process. An exquisite regulatory scheme has recently been proposed to modulate the action of transcription factors. Small peptides possessing a protein dimerization motif but lacking the DNA-binding motif form nonfunctional heterodimers with a group of specific TFs, inhibiting their transcriptional activation activities. Extensive searches for small proteins that have a similar structural organization in the databases revealed that small peptide-mediated transcription control is not an exceptional case but would be a regulatory mechanism occurring widespread in the Arabidopsis genome.




MINI-REVIEWS

Open Access Article

Towards effective resistance to Striga in African maize

Patrick J. Rich and Gebisa Ejeta
Pages 618 - 621
http://dx.doi.org/10.4161/psb.3.9.5750
Abstract | PDF

The fascinating biology of Striga parasitism is manifest through a series of signal exchanges between the parasite and its host. As an obligate root hemi-parasite, Striga development is cued to exudates and solutes of host roots but with negative ramifications on host plant health. Striga control in crops, via a variety of biotechnological approaches, needs to be based on increased understanding of this intricate biology. Maize has become the major cereal crop of Africa. However, this New World transplant has shown a paucity of Striga resistance characters relative to native sorghum. In this paper, we review growing evidence for maize genetic defenses against early pre-emergent phases of the Striga life cycle, when the tolls of parasitism are first manifest. Resistance characters first described in maize wild relatives have now been captured in Zea mays. The possible stacking of new and complementary sources of resistance in improved maize varieties targeted for Striga prone areas is discussed. An integrated approach combining genetic with other control measures is advocated with a more realistic view of the resource challenges prevalent in African agriculture.

Open Access Article

Heteromerization of Arabidopsis Kv channel α-subunits: Data and prospects

Linda Jeanguenin, Anne Lebaudy, Jérôme Xicluna, Carine Alcon, Eric Hosy, Geoffrey Duby, Erwan Michard, Benoît Lacombe, Ingo Dreyer and Jean Baptiste Thibaud
Pages 622 - 625
http://dx.doi.org/10.4161/psb.3.9.6209
Abstract | PDF

Potassium translocation in plants is accomplished by a large variety of transport systems. Most of the available molecular information on these proteins concerns voltage-gated potassium channels (Kv channels). The Arabidopsis genome comprises nine genes encoding α-subunits of Kv channels. Based on knowledge of their animal homologues, and on biochemical investigations, it is broadly admitted that four such polypeptides must assemble to yield a functional Kv channel. The intrinsic functional properties of Kv channel α-subunits have been described by expressing them in suitable heterologous contexts where homo-tetrameric channels could be characterized. However, due to the high similarity of both the polypeptidic sequence and the structural scheme of Kv channel α-subunits, formation of heteromeric Kv channels by at least two types of α-subunits is conceivable. Several examples of such heteromeric plant Kv channels have been studied in heterologous expression systems and evidence that heteromerization actually occurs in planta has now been published. It is therefore challenging to uncover the physiological role of this heteromerization. Fine tuning of Kv channels by heteromerisation could be relevant not only to potassium transport but also to electrical signaling within the plant.




REVIEW

Open Access Article

Transport and accumulation of flavonoids in grapevine (Vitis vinifera L.)

Enrico Braidot, Marco Zancani, Elisa Petrussa, Carlo Peresson, Alberto Bertolini, Sonia Patui, Francesco Macrì and Angelo Vianello
Pages 626 - 632
http://dx.doi.org/10.4161/psb.3.9.6686
Abstract | PDF

Flavonoids are a group of secondary metabolites widely distributed in plants that represent a huge portion of the soluble phenolics present in grapevine (Vitis vinifera L.). These compounds play different physiological roles and are often involved in protection against biotic and abiotic stress. Even if the flavonoid biosynthetic pathways have been largely characterized, the mechanisms of their transport and accumulation in cell wall and vacuole are still not completely understood. This review analyses the known mechanisms of flavonoid uptake and accumulation in grapevine, with reference to the transport models and membrane carrier proteins described in other plant species. The effect of different environmental factors on flavonoid biosynthesis and transporters is also discussed.




RESEARCH PAPERS

Open Access Article

The electrical response of Phaseolus vulgaris roots to abrupt exposure to hydroquinone

Christopher P. Keller, Richard R. Barkosky, Joshua E. Seil, Shanna A. Mazurek and Morgan L. Grundstad
Pages 633 - 640
http://dx.doi.org/10.4161/psb.3.9.5965
Abstract | PDF

Support for this project by National Institutes of Health (NIH, USA) Grant Number P20 RR016741 from the IDeA Network of Biomedical Research Excellence/Biomedical Research Infrastructure Network (INBRE/BRIN) Program of the National Center for Research Resources is gratefully acknowledged. The publication contents are, however, solely the responsibility of the authors and conclusions drawn are not to be seen as official views of the NIH.

Open Access Article

A mutation in the tomato DDB1 gene affects cell and chloroplast compartment size and CDT1 transcript

Nili Caspi, Ilan Levin, Daniel A. Chamovitz and Moshe Reuveni
Pages 641 - 649
http://dx.doi.org/10.4161/psb.3.9.6413
Abstract | PDF

Fruits harvested from tomato (Solanum lycopersicum) plants carrying mutations at the DAMAGED DNA BINDING PROTEIN 1 gene (SlDDB1; hp-1<,i> and hp-1^w) are characterized by significantly elevated levels of lycopene and several other phytonutrients. We hypothesize that the pleotropic effect on mutant Slddb1 are some general function of DDB1 protein on cell growth. The main objective of this research was to carry out functional analysis of the mutant SlDDB1 alleles both in-planta and ex-planta in comparison to their normal counterparts. Our major results indicate that: mutant Slddb1 seedlings exhibited delayed growth and smaller cell size, greater chloroplast density, smaller chloroplasts and higher concentration of chlorophyll.

Cotyledons cells of Slddb1 mutant also displayed abnormal stomatal pattern, reduced content of CDT1 transcript and altered response to cytokinin. Some of these observations were previously described to be connected to defects in cell-cycle control. Our results, coupled with former studies, also suggest that the CDD complex (composed of DDB1, DET1 and COP10) mediate the effect of light and cytokinin activity by possibly regulating the replication licensing factor CDT1 thus affecting both cell size and plastid multiplication.




ARTICLE ADDENDA

Open Access Article

Do ARG1 and ARL2 form an actin-based gravity-signaling chaperone complex in root statocytes?

Benjamin Harrison and Patrick H. Masson
Pages 650 - 653
http://dx.doi.org/10.4161/psb.3.9.5749
Abstract | PDF

Plants are acutely sensitive to the directional information provided by gravity. They have evolved statocytes, which are specialized cells that sense gravity and, upon integration of the corresponding information with that of other environmental stimuli, control the growth behavior of their organs. The cellular mechanisms that allow statocytes to sense and transduce gravitational information likely involve detecting the sedimentation of, or the tension/pressure exerted by, starch-filled amyloplasts - the presumptive statoliths - within their cytoplasm. Gravity signaling in root statocytes controls the direction of transport of signaling compounds, especially auxin, across the root cap, establishing a lateral gradient that is transmitted to cells in the elongation zone and results in gravitropic curvature. The Arabidopsis J-domain proteins ARG1 and ARL2 function as gravity-signal transducers in root statocytes. In the January issue of Plant Journal, we reported that ARG1 and ARL2 function non-redundantly in a common gravity signaling pathway required for accumulation of the auxin efflux facilitator PIN3 on the new bottom side of statocytes following gravity stimulation, and lateral redistribution of auxin toward the new lower flank of stimulated roots. Here we present data suggesting that ARG1 physically associates with ARL2, the J-domain co-chaperone HSC70, and actin in vivo. We briefly discuss potential mechanisms by which ARG1 and ARL2 might function in gravity signaling in light of this information.

Open Access Article

Biotic and abiotic stress responses through calcium-dependent protein kinase (CDPK) signaling in wheat (Triticum aestivum L.)

Aili Li, Xiang Wang, Charles H. Leseberg, Jizeng Jia and Long Mao
Pages 654 - 656
http://dx.doi.org/10.4161/psb.3.9.5757
Abstract | PDF

Calcium-dependent protein kinases (CDPKs) sense the calcium concentration changes in plant cells and play important roles in signaling pathways for disease resistance and various stress responses as indicated by emerging evidences. Among the 20 wheat CDPK genes studied, 10 were found to respond to draught, salinity and ABA treatments. Consistent with previous observations, one CDPK gene was shown to respond to multiple abiotic stresses in wheat suggesting that CDPKs could be converging points for multiple signaling pathways. Among the 12 wheat CDPK genes that were responsive to Blumeria graminis tritici (Bgt) infection or the treatment of hydrogen peroxide (H₂O₂), eight also responded to abiotic stresses, suggesting a cross-talk between biotic and abiotic stress signaling pathways. Phylogenetic analysis indicated that some of these genes were closely related to CDPKs from other species, whose functions have been partially studied, suggesting similar functions wheat CDPK genes. Combining the up-to-date knowledge of CDPK functions and our observations, a model was developed to project the possible roles of wheat CDPK genes in the signaling of biotic and abiotic stress responses.

Open Access Article

Viral suppression of RNA silencing by destabilization of ARGONAUTE 1

Diane Bortolamiol, Maghsoud Pazhouhandeh and Véronique Ziegler-Graff
Pages 657 - 659
http://dx.doi.org/10.4161/psb.3.9.5758
Abstract | PDF

RNA silencing is a manifestation of a ubiquitous phenomenon that acts, at least in plants and some insects, as a natural defense mechanism against viruses. As a counter-strategy, viruses have evolved to encode silencing suppressor proteins (SSPs) that can block the defense response and evade the host immunity. Although numerous SSP have been identified, little information is available on the molecular basis of their mode of action. Among SSPs, the polerovirus protein P0 functions as an F-box protein that targets an essential actor of the silencing pathway. Our work demonstrates that one of the main targets is ARGONAUTE 1 (AGO1), a key component of the RISC effector complex. By a physical interaction with AGO1, P0 mediates AGO1 protein degradation in planta. This is the first report of a plant virus that exploits components of the host ubiquitination machinery to overcome RNA silencing. This unusual mode of action may provide some clues concerning the mechanism governing phloem tropism of poleroviruses.

Open Access Article

Cytosolic heat shock protein 90 regulates heat shock transcription factor in Arabidopsis thaliana

Kenji Yamada and Mikio Nishimura
Pages 660 - 662
http://dx.doi.org/10.4161/psb.3.9.5775
Abstract | PDF

Plant survival requires the ability to acclimate to heat, which is involves the expression of heat-inducible genes. We found cytosolic heat shock protein (HSP) 90 serves as a negative regulator of heat shock transcription factor (HSF), which is responsible for the induction of heat-inducible genes in plant. Transient inhibition of HSP90 induces heat-inducible genes and heat acclimation in Arabidopsis thaliana seedlings. Most of upregulated genes by heat shock and HSP90 inhibitor treatments carry heat shock response element (HSE) in their promoter, which suggests that HSF participates in the response to HSP90 inhibition. A. thaliana HSP90.2 interacts with AtHsfA1d, which is one of the constitutively expressed HSFs in A. thaliana. Heat shock depleted cytosolic HSP90 activity, as shown by the activity of exogenously expressed glucocorticoid receptor (GR), which is a substrate of cytosolic HSP90. Thus, it appears that in the absence of heat shock, cytosolic HSP90 negatively regulates HsfA1. Upon heat shock, cytosolic HSP90 is transiently inactivated, and this may lead to the activation of HsfA1.

Open Access Article

Systemic nature of drought-tolerance in common bean

Víctor Montero-Tavera, Roberto Ruiz-Medrano and Beatriz Xoconostle-Cázares
Pages 663 - 666
http://dx.doi.org/10.4161/psb.3.9.5776
Abstract | PDF

The response to drought at the physiological and molecular levels was studied in two common bean varieties with contrasting susceptibility to drought stress. A number of genes were found to be up-regulated in the tolerant variety Pinto Villa relative to the susceptible cultivar, Carioca. The products of these genes fell in different functional categories. Further analyses of selected genes, consisting of their spatial differential expression and in situ mRNA accumulation patterns displayed interesting profiles. The drought-tolerant variety displayed a more developed root vasculature in drought conditions, when compared to the susceptible tropical bean Carioca. The in situ localization of three selected genes indicated the accumulation of their corresponding mRNAs in companion cells, sieve tubes and in developing phloem, suggesting that these, and/or the encoded proteins could constitute phloem-mobile signals. Indeed, a number of transcripts that are induced in response to water deficit accumulate in the phloem in other plant species, suggesting a general phenomenon. Moreover, the analysis of drought stress in plant varieties with contrasting tolerance to such stimulus will help to determine the role of differential expression of specific genes in response to such phenomenon, as well as other biochemical, morphological and physiological features in both cultivars.

Open Access Article

Probing allelochemical biosynthesis in sorghum root hairs

Scott R. Baerson, Agnes M. Rimando and Zhiqiang Pan
Pages 667 - 670
http://dx.doi.org/10.4161/psb.3.9.5779
Abstract | PDF

Allelopathic interaction between plants is thought to involve the release of phytotoxic allelochemicals by one species, thus inhibiting the growth of neighboring species in competition for limited resources. Sorgoleone represents one of the more potent allelochemicals characterized to date, and its prolific production in root hair cells of Sorghum spp. has made the investigation of its biosynthetic pathway ideally-suited for functional genomics investigations. Through the use of a recently-released EST data set generated from isolated Sorghum bicolor root hair cells, significant inroads have been made toward the identification of genes and the corresponding enzymes involved in the biosynthesis of this compound in root hairs. Here we provide additional information concerning our recent report on the identification of a 5-n-alk(en)ylresorcinol utilizing O-methyltransferase, as well as other key enzymes likely to participate in the biosynthesis of this important allelochemical.

Open Access Article

Peroxisome proliferation in Arabidopsis: The challenging identification of ligand perception and downstream signaling is closer

José León
Pages 671 - 673
http://dx.doi.org/10.4161/psb.3.9.5780
Abstract | PDF

Peroxisomes are subcellular organelles with multiple functions mediated by their plasticity and dynamic behavior in plants. Changes in their shape, size, number and enzyme content occur in response to developmental and metabolic cues as well as environmental conditions. The number of peroxisomes per cell is thus mainly determined by its capacity to proliferate. In mammals, peroxisome proliferators such as the hypolipidemic drug clofibrate are perceived by the Peroxisome Proliferator-Activated Receptors (PPARs) nuclear receptors. Therein, activated transcription of the peroxisome biogenesis PEX11 genes and the recruitment of dynamin-related proteins lead to peroxisome proliferation. We recently reported that Arabidopsis thaliana, despite of lacking a PPAR homolog protein, activated the proliferation of peroxisomes in response to clofibrate. Concomitantly, clofibrate activated the expression of wound-responsive genes through the jasmonic acid signaling master regulator COI1 F-box protein. Besides, wounding activated the expression of the peroxisome biogenesis-related PEX1 and PEX14 genes, but not of PEX11 or DRP3A, which analogously to mammals, code for the main regulators of peroxisome proliferation in Arabidopsis. Thus, wounding did not activate peroxisome proliferation. Noteworthy, jasmonic acid-treated plants contained fewer but larger peroxisomes. Despite of the cross-talk between clofibrate- and wound-induced signaling, the proliferation of peroxisomes and the wound-activated defense remained uncoupled.

Open Access Article

Role of OsPHR2 on phosphorus homoestasis and root hairs development in rice (Oryza sativa L.)

Ping Wu and X.M. Wang
Pages 674 - 675
http://dx.doi.org/10.4161/psb.3.9.5781
Abstract | PDF

AtPHR1 plays a central role in Pi-starvation signaling in Arabidopsis (Arabidopsis thaliana). Two PHR genes were isolated from rice and designated as OsPHR1 and OsPHR2 based on amino acid sequence homology to AtPHR1. Transgenic plants with overexpression and repression of OsPHR1 and OsPHR2, respectively, were used for investigation of roles of the genes in Pi-signaling pathway and Pi homeostasis under Pi-sufficient and deficient conditions. The results showed that both of the genes are involved in the Pi-signaling pathway, while overexpression of OsPHR2 mimics Pi-starvation stress with enhanced root elongation and proliferated root hairs, and results in the excessive accumulation of Pi in shoots under Pi-sufficient conditions. OsPHR2 regulated proliferation of root hair growth and root elongation suggests that OsPHR2 is involved in both systematic and local Pi-signaling pathways.

Open Access Article

Exploring the possibilities for radical pair effects in cryptochrome

Ilia A. Solov'yov, Danielle E. Chandler and Klaus Schulten
Pages 676 - 677
http://dx.doi.org/10.4161/psb.3.9.5809
Abstract | PDF

The ability of some animals to sense magnetic fields has long captured the human imagination. In our recent paper, we explored how radical pair effects in the protein cryptochrome may underlie the magnetic orientation sense of migratory birds. Here we explain our model and discuss its relationship to experimental results on plant cryptochromes, as well as discuss the next steps in refining our model, and explore alternate but related possibilities for modeling and understanding cryptochrome as a magnetic sensor.

Open Access Article

The nucleus as a chief cellular organizer and active defender in response to mechanical stimulation

Liang-Huan Qu and Meng-Xiang Sun
Pages 678 - 680
http://dx.doi.org/10.4161/psb.3.9.5810
Abstract | PDF

In addition to the mechanical forces of the external environment, the individual plant cell is also subject to multiple subtle biophysical forces that arise from neighboring cell growth and division within the tissue. To maintain a normal cell shape and division pattern, the plant cell is proposed to have the ability to sense and respond to repetitive subtle mechanical stimulations via nuclear-directed migration. It has been demonstrated that the nucleus is alert and highly sensitive to repetitive mechanical stimulations. Furthermore, the cytoplasm reacts to local mechanical stimulation in a compartmentalized fashion. The nucleus therefore plays a role as a chief organizer and active defender in response to mechanical stimulation. This finding provides new insight on the role of mechanical stimulation in regulating cell division and the consequent spatial positioning and shape of cells inside tissues. The finding also revealed that it necessitates further study into the reason for cytoplasmic functional compartmentalization in response to simulation in the context of cell evolution.

Open Access Article

PA, a stress-induced short cut to switch-on ethylene signalling by switching-off CTR1?

Christa Testerink, Paul B. Larsen, Fionn McLoughlin, Dieuwertje van der Does, John A.J. van Himbergen and Teun Munnik
Pages 681 - 683
http://dx.doi.org/10.4161/psb.3.9.5814
Abstract | PDF

Constitutive triple response 1 (CTR1) is a protein kinase that represses plant responses to ethylene. Recently, we have shown that CTR1 function is negatively regulated by the lipid second messenger phosphatidic acid (PA) in vitro. PA was shown to inhibit (1) CTR1’s protein kinase activity, (2) the intramolecular interaction between N-terminus and kinase domain, and (3) the interaction of CTR1 with the ethylene receptor ETR1. PA typically accumulates within minutes in response to biotic or abiotic stresses, which are known to induce ethylene formation. Although long-term treatment with ethephon does stimulate PA accumulation, our results show no fast increase in PA in response to ethylene. A speculative model is presented which explains how stress-induced PA formation could switch on downstream ethylene responses via interaction of the lipid with CTR1.

Open Access Article

Gene trap-based identification of a guard cell promoter in Arabidopsis

Priscilla Francia, Laura Simoni, Eleonora Cominelli, Chiara Tonelli and Massimo Galbiati
Pages 684 - 686
http://dx.doi.org/10.4161/psb.3.9.5820
Abstract | PDF

Preserving crop yield under drought stress is a major challenge for modern agriculture. To cope with the detrimental effects of water scarcity on crop productivity it is important to develop new plants with a more sustainable use of water and capable of higher performance under stress conditions. Transpiration through stomatal pores accounts for over 90% of water loss in land plants. Recent studies have increased our understanding of the networks that control stomatal activity and have led to practical approaches for enhancing drought tolerance. Genetic engineering of target genes in stomata requires effective expression systems, including suitable promoters, because constitutive promoters (i.e. CaMV35S) are not always functional or can have negative effects on plant growth and productivity. Here we describe the identification of the CYP86A2 guard cell promoter and discuss its potential for gene expression in stomata.

Open Access Article

Signaling control of SOS1 mRNA stability

Jiafu Jiang and Huazhong Shi
Pages 687 - 688
http://dx.doi.org/10.4161/psb.3.9.5821
Abstract | PDF

Regulation of mRNA decay rates appears to be an important control point in determining the abundance of gene transcripts. Rapid change in decay rates of mRNAs could provide prompt responses of the plants to environmental fluctuations. SOS1 is a plasma-membrane Na⁺/H⁺ antiporter crucial for salt tolerance in Arabidopsis. In our recent paper in Plant Journal, we have shown that SOS1 mRNA is inherently instable at normal growth conditions, but its stability is substantially elevated by salt and oxidative stress treatments. Salt stress-induced SOS1 mRNA stability is mediated by reactive oxygen species (ROS) produced, at least in part, through NADPH oxidases. We proposed a hypothetical model for the signaling pathway controlling SOS1 mRNA stability. In this addendum, we discuss the possible involvement of other components in conferring inherent instability and stress-induced stability of SOS1 mRNA.

Open Access Article

The involvement of the Arabidopsis CRT1 ATPase family in disease resistance protein-mediated signaling

Hong-Gu Kang and Daniel F. Klessig
Pages 689 - 690
http://dx.doi.org/10.4161/psb.3.9.5822
Abstract | PDF

Resistance (R) gene-mediated immunity provides plants with rapid and strain-specific protection against pathogen infection. Our recent study using the genetically tractable Arabidopsis and turnip crinkle virus (TCV) pathosystem revealed a novel component, named CRT1 (compromised for recognition of the TCV CP), that is involved in general R gene-mediated signaling, including that mediated by HRT, an R gene against TCV. The Arabidopsis CRT1 gene family contains six additional members, of which two share high homology to CRT1 (75 and 81% a.a. identity); either CRT1 or its closest homolog restore the cell death phenotype suppressed by crt1. Analysis of single knock-out mutants for CRT1 and its closest homologs suggest that each may have unique and redundant functions. Here, we provide insight into the screening conditions that enabled identification of a mutant gene despite the presence of functionally redundant family members. We also discuss a potential mechanism that may regulate the interaction between CRT1 and R proteins.

Open Access Article

The search for the salicylic acid receptor led to discovery of the SAR signal receptor

Dhirendra Kumar and Daniel F. Klessig
Pages 691 - 692
http://dx.doi.org/10.4161/psb.3.9.5844
Abstract | PDF

Systemic acquired resistance (SAR) is a state of heightened defense which is induced throughout a plant by an initial infection; it provides long-lasting, broad-spectrum resistance to subsequent pathogen challenge. Recently we identified a phloem-mobile signal for SAR which has been elusive for almost 30 years. It is methyl salicylate (MeSA), an inactive derivative of the defense hormone, salicylic acid (SA). This discovery resulted from extensive characterization of SA-binding protein 2 (SABP2), a protein whose high affinity for SA and extremely low abundance suggested that it might be the SA receptor. Instead we discovered that SABP2 is a MeSA esterase whose function is to convert biologically inactive MeSA in the systemic tissue to active SA. The accumulated SA then activates or primes defenses leading to SAR. SABP2’s esterase activity is inhibited in the initially/primary infected tissue by SA binding in its active site; this facilitates accumulation of MeSA, which is then translocated through the phloem to systemic tissue for perception and processing by SABP2 to SA. Thus, while SABP2 is not the SA receptor, it can be considered the receptor for the SAR signal. This study of SABPs not only illustrates the unexpected nature of scientific discoveries, but also underscores the need to use biochemical approaches in addition to genetics to address complex biological processes, such as disease resistance.

Addendum to: Park S-W, Kaimoyo E, Kumar D, Mosher S, Klessig DF. Methyl salicylate is a critical mobile signal for plant systemic acquired resistance. Science 2007; 318:113-6.

Open Access Article

Arabidopsis ACBP1 overexpressors are Pb(II)-tolerant and accumulate Pb(II)

Shi Xiao and Mee-Len Chye
Pages 693 - 694
http://dx.doi.org/10.4161/psb.3.9.5845
Abstract | PDF

In our recent paper in the Plant Journal, we demonstrated that Arabidopsis thaliana acyl-CoA-binding protein ACBP1 binds lead [Pb(II)], its mRNA is induced by Pb(II)-treatment and transgenic Arabidopsis overexpressing ACBP1 are conferred Pb(II) tolerance and accumulate Pb(II). Our results suggest that ACBP1 overexpressors are potentially useful for applications in phytoremediation. Since very few plant proteins that bind and accumulate Pb(II) have been identified, our findings provide a feasible method in phytoremediating Pb(II).

Addendum to: Xiao S, Gao W, Chen QF, Ramalingam S, Chye ML. Overexpression of membrane-associated acyl-CoA-binding protein ACBP1 enhances lead tolerance in Arabidopsis. Plant J 2008; doi:10.1111/j.1365-313X.2008.03402.x

Open Access Article

Is there a link between protein kinase CK2 and auxin signaling?

Jordi Moreno-Romero and M. Carmen Martínez
Pages 695 - 697
http://dx.doi.org/10.4161/psb.3.9.6343
Abstract | PDF

Protein kinase CK2 is a pleitropic Ser/Thr kinase present in all eukaryotes. In order to study the effects of CK2 depletion on plant development, we have recently generated Arabidopsis transgenic plants expressing a CK2α-inactive mutant under the control of an inducible promoter. Our results showed that continuous expression of the transgene had a dominant negative effect and was lethal for Arabidopsis plants. Overexpression of the CK2α-inactive subunit provoked cell cycle arrest, by perturbation of both G1/S and G2 cell-cycle phases. The effects on cell division were particularly strong in root meristems, causing inhibition of lateral root formation even when the mutant protein was transiently induced. Processes that rely on cell expansion, such as hypocotyl elongation in dark-grown seedlings, were also strongly affected. We propose that CK2 regulates auxin-signaling pathways.

Addendum to: Moreno-Romero J, Carme Espunya M, Platara M, Ariño J, Carmen Martínez M. A role for protein kinase CK2 in plant development: evidence obtained using a dominant-negative mutant. Plant J. 2008; In press.

Open Access Article

Voltage, reactive oxygen species and the influx of calcium

Jennifer C. Mortimer, Anuphon Laohavisit, Henk Miedema and Julia M. Davies
Pages 698 - 699
http://dx.doi.org/10.4161/psb.3.9.6405
Abstract | PDF

The apical plasma membrane of young Arabidopsis root hairs has recently been found to contain a depolarisation-activated Ca²⁺ channel, in addition to one activated by hyperpolarisation. The depolarisation-activated Ca²⁺ channel may function in signalling but the possibility that the root hair apical plasma membrane voltage may oscillate between a hyperpolarised and depolarised state suggests a role in growth control. Plant NADPH oxidase activity has yet to be considered in models of oscillatory voltage or ionic flux despite its predicted electrogenicity and voltage dependence. Activity of root NADPH oxidase was found to be stimulated by restricting Ca²⁺ influx, suggesting that these enzymes are involved in sensing Ca²⁺ entry into cells.

Addendum to: Miedema H, Demidchik V, Véry A-A, Bothwell JHF, Brownlee C, Davies JM. Two voltage-dependent calcium channels co-exist in the apical plasma membrane of Arabidopsis thaliana root hairs. New Phytol 2008; doi:10.1111/j.1469-8137.2008.02465.x

Open Access Article

Vacuolar and cytoskeletal dynamics during elicitor-induced programmed cell death in tobacco BY-2 cells

Takumi Higaki, Yasuhiro Kadota, Tatsuaki Goh, Teruyuki Hayashi, Natsumaro Kutsuna, Toshio Sano, Seiichiro Hasezawa and Kazuyuki Kuchitsu
Pages 700 - 703
http://dx.doi.org/10.4161/psb.3.9.6431
Abstract | PDF

Responses of plant cells to environmental stresses often involve　morphological changes, differentiation and redistribution of various organelles and cytoskeletal network. Tobacco BY-2 cells provide excellent model system for in vivo imaging of these intracellular events. Treatment of the cell cycle-synchronized BY-2 cells with a proteinaceous oomycete elicitor, cryptogein, induces highly synchronous programmed cell death (PCD) and provide a model system to characterize vacuolar and cytoskeletal dynamics during the PCD. Sequential observation revealed dynamic reorganization of the vacuole and actin microfilaments during the execution of the PCD. We further characterized the effects cryptogein on mitotic microtubule organization in cell cycle-synchronized cells. Cryptogein treatment at S phase inhibited formation of the preprophase band, a cortical microtubule band that predicts the cell division site. Cortical microtubules kept their random orientation till their disruption that gradually occurred during the execution of the PCD twelve hours after the cryptogein treatment. Possible molecular mechanisms and physiological roles of the dynamic behavior of the organelles and cytoskeletal network in the pathogenic signal-induced PCD are discussed.

Addendum to: Higaki T, Goh T, Hayshi T, Kutsuna N, Kadota Y, Hasezawa S, Sano T, Kuchitsu K. Elicitor-induced cytoskeletal rearrangement relates to vacuolar dynamics and execution of cell death: In vivo imaging of hypersensitive cell death in tobacco BY-2 cells. Plant Cell Physiol 2007; 48:1414-25.

Open Access Article

Specificity in the interaction between an epibiotic clavicipitalean fungus and its convolvulaceous host in a fungus/plant symbiotum

Ulrike Steiner, Sabine Hellwig and Eckhard Leistner
Pages 704 - 706
http://dx.doi.org/10.4161/psb.3.9.6432
Abstract | PDF

Ipomoea asarifolia and Turbina corymbosa (Convolvulaceae) are associated with epibiotic clavicipitalean fungi responsible for the presence of ergoline alkaloids in these plants. Experimentally generated plants devoid of these fungi were inoculated with different epibiotic and endophytic fungi resulting in a necrotic or commensal situation. A symbiotum of host plant and its respective fungus was best established by integration of the fungus into the morphological differentiation of the host plant. This led us to suppose that secretory glands on the leaf surface of the host plant may play an essential role in ergoline alkaloid biosynthesis which takes place in the epibiotic fungus.

Addendum to: Markert A, Steffan N, Ploss K, Hellwig S, Steiner U, Drewke C, Li S, Boland W, Leistner E. Biosynthesis and accumulation of ergoline alkaloids in a mutualistic association between Ipomoea asarifolia (Convolvulaceae) and a clavicipitalean fungus. Plant Physiol 2008; 147:296-305.

and

Steiner U, Ahimsa-Müller MA, Markert A, Kucht S, Groß J, Kauf N, Kuzma M, Zych M, Lamsöft M, Furmanowa M, Knoop V, Drewke C, Leistner E. Molecular characterisation of a seed transmitted clavicipitaceous fungus occurring on dicotyledonous plants (Convolvulaceae). Planta 2006; 224:533-44.

Open Access Article

Are extracellular matrix surface network components involved in signalling and protective function?

Marzena Popielarska-Konieczna, Małgorzata Kozieradzka-Kiszkurno, Joanna Świerczyńska, Grzegorz Góralski, Halina Ślesak and Jerzy Bohdanowicz
Pages 707 - 709
http://dx.doi.org/10.4161/psb.3.9.6433
Abstract | PDF

Endosperm is an interesting model for in vitro experiments, because of its unique origin, development and ploidy level. Here we used Actinidia deliciosa endosperm-derived callus to investigate morphology, histology and chemistry of extracellular matrix (ECM) structures in morphogenically stable tissue from long - term culture. SEM and TEM analysis showed that ECM is a heterogenous layer which consists of amorphous, dark – staining material, osmiophilic granules and reticulated fibres outside the outer callus cell wall. This structure may serve as a structural marker of morphogenic competence in endosperm – derived callus, because of its presence on the surface of callus forming morphogenic domains and its disappearance during organ growth. Based on immunolabelling, histochemistry, solvent and enzyme treatments, we suggest that pectins and lipids are components of the ECM layer. These results might indicate protective, water retention and/or cell communication functions for this ECM layer.

Addendum to: Popielarska-Konieczna M, Kozieradzka-Kiszkurno M, Świerczyńska J, Góralski G, Ślesak H, Bohdanowicz J. Ultrastructure and histochemical analysis of extracellular matrix surface network in kiwifruit endosperm-derived callus culture. Plant Cell Rep 2008; 27:1137-45.

Open Access Article

Disordered plant LEA proteins as molecular chaperones

Denes Kovacs, Bianka Agoston and Peter Tompa
Pages 710 - 713
http://dx.doi.org/10.4161/psb.3.9.6434
Abstract | PDF

Plants often respond to abiotic stresses by the increased expression of LEA (late embryogenesis abundant) proteins, so called because they also accompany seed formation. Whereas the cellular function of LEA proteins in mitigating the damage caused by stress is clear, the molecular mechanisms of their action are rather enigmatic. Several models have been developed, based on their putative activities as ion sinks, stabilizers of membrane structure, buffers of hydrate water, antioxidants, and/or chaperones. Due to their known structural flexibility, this latter idea has received little experimental attention thus far. Recently, however, it has been suggested that intrinsically disordered proteins (IDPs) may exert chaperone activity by an “entropy transfer” mechanism. In our subsequent study published in the May issue of Plant Physiology, we provided evidence that two group 2 LEA proteins, ERD (early response to dehydration) 10 and 14, are potent molecular chaperones. This observation may have far-reaching implications, as it may explain how LEA proteins of ill-defined structures protect plant cells during dehydration, and it may also lead to the general experimental validation of the entropy transfer model of disordered chaperones.

Addendum to: Kovacs D, Kalmar E, Torok Z, Tompa P. Chaperone activity of ERD10 and ERD14, two disordered stress-related plant proteins. Plant Physiol. 2008; 147: 381–390.

Open Access Article

Induction of serotonin accumulation by feeding of rice striped stem borer in rice leaves

Atsushi Ishihara, Yumi Hashimoto, Hisashi Miyagawa and Kyo Wakasa
Pages 714 - 716
http://dx.doi.org/10.4161/psb.3.9.6456
Abstract | PDF

Tryptophan (Trp)-related secondary metabolism has been implicated in the defense against pathogen infection and insect feeding in various gramineous species. Recently, we also reported that rice plant accumulated serotonin and tryptamine as well as their amide compounds coupled with phenolic acids in response to the infection by fungal pathogen. These compounds were likely to play an important role in the formation of physical barrier to the invading pathogens. To extend our study to elucidate the defensive role of Trp-derived secondary metabolism in gramineous plants, we examined in this study whether it is activated in response to herbivore attack as well. Third leaves of rice plant were fed on by third instar larvae of rice striped stem borer for 24 h or 48 h. The analysis of four Trp-derived metabolites including tryptamine, serotonin feruloyltryptamine (FerTry) and p-coumaroylserotonin (CouSer) by liquid chromatography coupled with tandem mass spectrometry revealed that their contents clearly increased in response to the larvae feeding. The respective amounts of tryptamine, serotonin, FerTry and CouSer in the larvae-fed leaves were 12-, 3.5-, 33-, and 140-fold larger than those in control leaves 48 h after the start of feeding.

Addendum to: Ishihara A, Hashimoto Y, Tanaka C, Dubouzet JG, Nakao T, Matsuda F, Nishioka T, Miyagawa H, Wakasa K. The tryptophan pathway is involved in the defense responses of rice against pathogenic infection via serotonin production. Plant J 2008; 54:481-95.

Open Access Article

Rac1 function during fucoid development

Rachel A. Muzzy and Whitney E. Hable
Pages 717 - 719
http://dx.doi.org/10.4161/psb.3.9.6457
Abstract | PDF

Morphogenesis in fucoid algae begins with adhesive secretion and rhizoid germination, developmental events that secure the alga within the intertidal zone. The importance of the actin cytoskeleton during these processes has been well established; but in general, little is known about actin regulation within the stramenopile lineage. Based on conserved strategies for regulation of actin in other lineages, co-localization of the Arp2/3 complex with actin structures that are essential for rhizoid formation may implicate members of the Rho family of small GTPases in the signaling pathway(s) regulating actin polymerization during fucoid development. Our lab recently demonstrated Rac1 dependent regulation of endomembrane polarization, polarization of adhesive secretion, germination and tip growth in the fucoid brown alga Silvetia compressa. We also present new evidence revealing Rac1 localization during germination in S. compressa, and show that membrane localization is essential for proper Rac1 function.

Addendum to: Hable WE, Reddy S, Julien L. The Rac1 inhibitor, NSC23766, depolarizes adhesive secretion, endomembrane cycling, and tip growth in the fucoid alga, Silvetia compressa. Planta 2008; 227:991-1000.

Open Access Article

Elucidation of the genomic basis of indirect plant defense against insects

Joshua S. Yuan, Tobias G. Köllner, Greg Wiggins, Jerome Grant, Nan Zhao, Xiaofeng Zhuang, Jörg Degenhardt and Feng Chen
Pages 720 - 721
http://dx.doi.org/10.4161/psb.3.9.6468
Abstract | PDF

Using airborne signals to attract herbivore predators and parasitoids is an important strategy that plants use in defense against herbivorous insects. The volatiles involved in this indirect plant defense are often chemically complex and variable across species. We recently established rice as a model for studying the molecular and genomic basis of volatile-mediated indirect plant defense. Rice plants when damaged by fall armyworm larvae become highly attractive to parasitic wasps. The volatiles potentially responsible for parasitoid attraction were determined to be a blend of compounds predominated by terpenoids, of which S-linalool is the most abundant. Racemic linalool alone was shown to be effective in attracting parasitic wasps. By combining volatile profiling and microarray analysis, a catalog of candidate genes for volatile biosynthesis was identified. Three genes encoding terpene synthases were biochemically characterized. They are responsible for the production of the majority of volatile terpenes released from insect-damaged rice plants. Additional candidate genes are being currently characterized for their role in production of other insect-induced volatiles from rice plants. Identification of a complete set of key genes for synthesizing herbivory-induced volatiles in rice will provide an important reference for comparative study of this important defense trait across a variety of plant species.

Addendum to: Yuan JS, Köllner TG, Wiggins G, Grant J, Degenhardt J, Chen F. Molecular and genomic basis of volatile-mediated indirect defense against insects in rice. Plant J 2008; In press.

Open Access Article

Has Arabidopsis SWEETIE protein a role in sugar flux and utilization?

Nicolas Veyres, Mitsuko Aono, Brigitte S. Sangwan-Norree and Rajbir S. Sangwan
Pages 722 - 725
http://dx.doi.org/10.4161/psb.3.9.6470
Abstract | PDF

In plants, sugars affect growth and development and play an important role in the intricate machinery of signal transduction. Understanding the mechanisms behind the flux of sugar in the plant is of central interest. We recently characterized an Arabidopsis mutant: sweetie, which is defective in the control of growth and development, sterile, shows premature senescence and affects sugar metabolism. Our microarray analysis showed that 15 genes annotated as sugar transporter related proteins were found to be upregulated in sweetie while one sugar transporter gene was found to be downregulated. Most of them are unspecified sugar transporters but four genes have been annotated as monosaccharide transporters and one has been annotated as a disaccharide transporter. Moreover, as computer analyses predicted that SWEETIE might be a membrane protein and might have a function of glycosyl transferase, our data suggest that SWEETIE could be involved in the general control of sugar flux and modulates many important processes such as morphogenesis, flowering, stress responses, and senescence.

Addendum to: Veyres N, Danon A, Aono M, Galliot S, Yashoda BK, Diet A, Grandmottet F, Tamaoki M, Lesur D, Pilard S, Boitel-Conti M, Sangwan-Norreel BS, Sangwan RS. The Arabidopsis sweetie mutant is affected in carbohydrate metabolism and defective in the control of growth, development and senescence. Plant Journal 2008; doi: 10.1111/j.1365-313X.2008.03541.x

Open Access Article

AtMSL9 and AtMSL10: Sensors of plasma membrane tension in Arabidopsis roots

Rémi Peyronnet, Elizabeth S. Haswell, Hélène Barbier-Brygoo and Jean-Marie Frachisse
Pages 726 - 729
http://dx.doi.org/10.4161/psb.3.9.6487
Abstract | PDF

Plant cells, like those of animals and bacteria, are able to sense physical deformation of the plasma membrane. Mechanosensitive (MS) channels are proteins that transduce mechanical force into ion flux, providing a mechanism for the perception of mechanical stimuli such as sound, touch and osmotic pressure. We recently identified AtMSL9 and AtMSL10, two mechanosensitive channels in Arabidopsis thaliana, as molecular candidates for mechanosensing in higher plants. AtMSL9 and AtMSL10 are members of a family of proteins in Arabidopsis that are related to the bacterial MS channel MscS, termed MscS-Like (or MSL). MscS (Mechanosensitive channel of Small conductance) is one of the best-characterized MS channels, first identified as an electrophysiological activity in the plasma membrane (PM) of giant E. coli spheroplasts. Activation of MscS is voltage-independent, but responds directly to tension applied to the membrane and does not require other cellular proteins for this regulation. MscS family members are widely distributed throughout bacterial and archaeal genomes, are present in all plant genomes yet examined, and are found in selected fungal genomes. MscS homolgues have not yet been identified in animals.

We previously showed that in wild type protoplasts from the Arabidopsis root, AtMSL9 and AtMSL10 function cooperatively to provide a characteristic WT activity. In this paper, we further investigate the function of AtMSL9 and AtMSL10. We analyze individual protoplasts and argue that in WT cells AtMSL9 and AtMSL10 can function either in cooperation or independently. We also compare the electrophysiological properties of these two channels with that of their bacterial and algal counterparts, and discuss their possible function in planta.

Addendum to: Haswell ES, Peyronnet R, Barbier-Brygoo H, Meyerowitz EM, Frachisse J-M. Two MscS homologs provide mechanosensitive channel activities in the Arabidopsis root. Curr Biol 2008; 18:730-4.

Open Access Article

Long-distance movement and differential targeting of microRNA399s

Shu-I Lin and Tzyy-Jen Chiou
Pages 730 - 732
http://dx.doi.org/10.4161/psb.3.9.6488
Abstract | PDF

We have previously demonstrated that miR399s control phosphate (Pi) homeostasis by regulating the expression of a ubiquitin-conjugating E2 enzyme (UBC24/PHO2) in Arabidopsis. Changes in miR399-dependent PHO2 gene expression modulate Pi uptake, allocation and remobilization. More recently, we provided evidence that miR399s are able to move in the phloem stream and across grafting junctions from the scions overexpressing miR399 to the wild-type rootstocks. Movement of miR399s serves as a long-distance signal to report and balance the Pi status between shoots and roots. Of note, results from grafting experiments indicate that miR399b is less efficient in cleaving the PHO2 mRNA than is miR399f, despite the similar mobility of the two miR399s. We propose that nucleotide 13 of miR399s, which gives rise to the sequence variation among different miR399 species, could be involved in regulating the abundance of PHO2 mRNA through sequence complementarity to the target sequences of PHO2 mRNA and mimicking target sequence of At4/IPS1 noncoding RNAs.

Addendum to: S-I Lin, S-F Chiang, W-Y Lin, J-W Chen, C-Y Tseng, P-C Wu and T-J Chiou. Regulatory network of microRNA399 and PHO2 by systemic signaling. Plant Physiol 2008; 147:732-46.

Open Access Article

Cell wall remodeling in Arabidopsis stamen abscission zones: Temporal aspects of control inferred from transcriptional profiling

Coralie C. Lashbrook and Suqin Cai
Pages 733 - 736
http://dx.doi.org/10.4161/psb.3.9.6489
Abstract | PDF

Organ shedding requires cell separation within abscission zones (AZs). Functional genomic AZ studies have been limited by their small size and low incidence. Optimization of laser capture microdissection (LCM) for AZs and other specialized cell types in Arabidopsis allowed recent characterization of the floral stamen AZ transcriptome responding to a developmental shedding cue. Analyses focused on 551 AZ transcripts (AZ₅₅₁) that were regulated at the highest statistical significance (P<=0.0001) over five stages of stamen development spanning pre-pollination to organ shed. Here, we seek a fuller understanding of AZ integrity control by relaxing P value restrictions on statistical significance ten-fold to generate an expanded population of 1461 stamen transcripts (AZ₁₄₆₁). Cell wall remodeling functions in AZ₁₄₆₁ are significantly over-represented relative to all transcripts represented on the whole genome GeneChip. Hierarchical clustering of gene expression data corresponding to cell wall-related transcripts suggests a temporal model for AZ remodeling in Arabidopsis stamens destined to abscise.

Addendum to: Cai S, Lashbrook CC. Stamen abscission zone transcriptome profiling reveals new candidates for abscission control. Enhanced retention of floral organs in transgenic plants overexpressing Arabidopsis zinc finger protein2. Plant Physiol 2008; 146:1305-21.

Open Access Article

The relationship between increased growth and resistance induced in plants by root colonizing microbes

Michal Shoresh and Gary E. Harman
Pages 737 - 739
http://dx.doi.org/10.4161/psb.3.9.6605
Abstract | PDF

Trichoderma spp. are effective biocontrol agents for numerous foliar and root phytopathogens, and some are also known for their abilities to enhance systemic resistance to plant diseases as well as overall plant growth. Root colonization with T. harzianum strain T22 induces large changes in the proteome of shoots of maize seedlings (Zea mays) even though T22 is present only on roots; changes also were recorded in the roots. In shoots, we identified 91 of 114 upregulated and 30 of 50 downregulated proteins. In roots, 20 upregulated and 11 downregulated proteins were found and 17 and eight, respectively, were identified. Classification of proteins differentially expressed in both shoots and roots revealed that the largest number of upregulated proteins was involved in carbohydrate metabolism; in shoots, some upregulated proteins were involved in photosynthesis. Increases in these protein classifications suggest enhanced respiratory and photosynthetic rates. These changes may be required for the enhanced growth response induced by colonization of Trichoderma following seed or soil treatments. Stress and defense related proteins that were upregulated probably are related to the enhanced resistance conferred by the Trichoderma inoculation. We suggest that Trichoderma induces both increased growth, which is mediated by an increase in photosynthetic and respiratory rates, and systemic induced resistance. These two general effects may be mediated by different elicitors.

Addendum to: Shoresh M, Harman GE. The molecular basis of shoot responses of maize seedlings to Trichoderma harzianum T22 inoculation of the root: A proteomic approach. Plant Physiol 2008; In press.

Open Access Article

Exploiting Arabidopsis leaf orthistichy to dissect signalling pathways during plant-pathogen interactions

Andrew J. Love, Karen Roberts, Mark A. Hooks, A. Deri Tomos and Joel J. Milner
Pages 740 - 742
http://dx.doi.org/10.4161/psb.3.9.6632
Abstract | PDF

Upon pathogen exposure, plants activate a complex but tightly co-ordinated suite of responses. Investigation of these responses is often hindered by sampling methodologies, whereby analysis of whole plant tissues may disguise what is actually occurring in smaller areas of the leaf. In our New Phytologist (September 2007) paper we identified an approach where we could determine exquisitely where Cauliflower Mosaic Virus (CaMV) was and where it was travelling to; coupled to the accurate monitoring of tightly co-ordinated defence gene regulation. Such an approach has helped us to further characterize the role of plant defence and the subsequent suppression of these defences by the pathogen.

Addendum to: Roberts K, Love AJ, Laval V, Laird J, Tomos AD, Hooks MA, Milner JJ. Long-distance movement of Cauliflower mosaic virus and host defence responses in Arabidopsis follow a predictable pattern that is determined by the leaf orthostichy. New Phytol 2007; 175:707-17.

Open Access Article

Plant cell walls: New insights from ancient species

Iben Sørensen and William G.T. Willats
Pages 743 - 745
http://dx.doi.org/10.4161/psb.3.9.6633
Abstract | PDF

Cell walls are a defining feature of plants and have numerous crucial roles in growth and development. They are also the largest source of terrestrial biomass and have many important industrial applications – ranging from bulk products to functional food ingredients. There is considerable interest in the structure and functions of cell walls, and in the evolution of their remarkably complex polysaccharide structures. The grasses and cereals (order Poales), have long been regarded as being unique in that their cell walls contain an unbranched homopolymer, (1→3)(1→4)-β-D-glucan, in which short blocks of (1→4)-linked β-D-Glcp are joined by occasional (1→3)-linkages. This mixed linkage glucan (MLG) has been the subject of extensive research because of the economic importance of several Poales species including rice, barley and wheat and because MLG has proven health benefits. The recent discovery of MLG in horsetails (Equisetales order) was therefore significant and has prompted a re-evaluation of some of the current views on cell wall evolution and structural diversity.

Addendum to: Sørensen I, Pettolino FA, Wilson SM, Doblin MS, Johansen B, Bacic A, Willats WGT. Mixed-linkage (1→3),(1→4)-β-D-glucan is not unique to the Poales and is an abundant component of Equisetum arvense cell walls. Plant J 2008; 54:510-21.

Open Access Article

Toxic and signalling effects of oxalic acid: Oxalic acid—Natural born killer or natural born protector?

Arnaud Lehner, Patrice Meimoun, Rafik Errakhi, Karine Madiona, Mustapha Barakate and François Bouteau
Pages 746 - 748
http://dx.doi.org/10.4161/psb.3.9.6634
Abstract | PDF

Oxalic acid is thought to be a key factor of the early pathogenic stage in a wide range of necrotrophic fungi. We have recently published that oxalic acid induces Programmed Cell Death (PCD) in Arabidopsis thaliana cells. This cell death results from an early anionic efflux which is a prerequisite for the synthesis of ethylene and the PCD. Complementary experiments have been carried out by using seedlings of A. thaliana. The effects of millimolar concentrations of oxalic acid were analysed on A. thaliana seedlings. A treatment with a 3 mM oxalic acid solution does not alter the development of the plants but induces the transcription of defence related genes which are anion channel dependant. Moreover, our results suggest that a pre-treatment of the seedlings with oxalic acid is able to confer the resistance of A. thaliana against Sclerotium rolfsii. Regarding our results, we suggest that oxalic acid plays two distinct roles, depending on the concentration: a high concentration of oxalic acid induces a large PCD and then contribute to the progression of the fungi. However, at low concentration it is able to induce the establishment of a resistance of the plant against the fungi.

Addendum to: Errakhi R, Meimoun P, Lehner A, Vidal G, Briand J, Corbineau F, Rona JP, Bouteau F. Anion channel activity is necessary to induce ethylene synthesis and programmed cell death in response to oxalic acid. J Exp Bot 2008; doi:10.1093/jxb/ern166.

Open Access Article

Two different mechanisms control ethylene sensitivity in Arabidopsis via the regulation of EBF2 expression

Mineko Konishi and Shuichi Yanagisawa
Pages 749 - 751
http://dx.doi.org/10.4161/psb.3.9.6640
Abstract | PDF

EIN3 is a key transcription factor in the ethylene signaling pathway in Arabidopsis and its action is controlled by SCF^EBF1/2 complex-mediated ubiquitination and subsequent 26S proteasome-dependent degradation. Our recent study revealed that ethylene signaling is regulated by a negative feedback system involving the direct activation of the EBF2 promoter by EIN3. This negative feedback loop likely modulates both the magnitude of the response to ethylene and the recovery after its withdrawal. The sequence downstream of the EBF2 stop codon was also found to play a role in determining the EBF2 expression levels independently of ethylene signaling. The reduction in EBF2 expression via the function of this sequence was suggested to be important for coupling the EBF2 expression levels to growth control. Two different mechanisms thus appear to be involved in determining ethylene sensitivity in Arabidopsis.

Addendum to: Konishi M, Yanagisawa S. Ethylene signaling in Arabidopsis involves feedback regulation via the elaborate control of EBF2 expression by EIN3. Plant J 2008; In press.

Open Access Article

NSP-Interacting GTPase: A cytosolic protein as cofactor for nuclear shuttle proteins

Claudine M. Carvalho, Joao Paulo B. Machado, Francisco Murilo Zerbini and Elizabeth P.B. Fontes
Pages 752 - 754
http://dx.doi.org/10.4161/psb.3.9.6641
Abstract | PDF

Despite the significant progress in the identification of essential components of the nuclear transport machinery, some events of this process are still unclear. Particularly, functional information about the release of nuclear-exported macromolecules at the cytoplasmic side of the nuclear pore complex and their subsequent trans-cytoplasmic movement is lacking. Recently, we identified a cytoplasmic GTPase, designated NIG (NSP-interacting GTPase), which may play a relevant role in these processes. NIG interacts in vivo with the geminivirus NSP and promotes the translocation of the viral protein from the nucleus to the cytoplasm where it is redirected to the cell surface to interact with the viral movement protein, MP. Here we position the NIG function into the mechanistic model for the intracellular trafficking of viral DNA and discuss the putative role of NIG in general cellular nucleocytoplasmic transport of nucleic acid-protein complexes.

Addendum to: Carvalho CM, Fontenelle MR, Florentino LH, Santos AA, Zerbini FM, Fontes EPB. A novel nucleocytoplasmic traffic GTPase identified as a functional target of the bipartite geminivirus nuclear shuttle protein. Plant J 2008; DOI: 10.1111/j.1365-313X.2008.03556.x.




MEETING REPORT

Open Access Article

The 4^th Plant Neurobiology Symposium: An overview

Gladys I. Cassab
Pages 755 - 757
http://dx.doi.org/10.4161/psb.3.9.6575
PDF