Table of Contents

Volume 5, Issue 3

  March 2010

  Pages 209 - 335

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 Issue Catalogue (MARC XML)

MINI-REVIEWS

Open Access Article

NO says more than ‘YES’ to salt tolerance: Salt priming and systemic nitric oxide signaling in plants

Athanassios Molassiotis, Georgia Tanou and Grigorios Diamantidis
Pages 209 - 212
http://dx.doi.org/10.4161/psb.5.3.10738
Abstract | PDF

Nitric oxide (NO) is now recognized as an important signaling molecule and there has been an increasing bulk of studies regarding the various functions of NO in plants exposed to environmental stimulus. There is also emerging evidence, although not extensive, that NO plays systemic signaling roles during the establishment of salt tolerance in many plant species. In this mini-review, we highlight several candidate mechanisms as being functional in this NO systemic signaling action. In addition, we outline data supporting that plants possess prime-like mechanisms that allow them to memorize previous NO exposure events and generate defense responses following salt stress.

Open Access Article

Plant actin cytoskeleton remodeling by plant parasitic nematodes

Janice de Almeida Engler, Natalia Rodiuc, Andrei Smertenko and Pierre Abad
Pages 213 - 217
http://dx.doi.org/10.4161/psb.5.3.10741
Abstract | PDF

Cytoskeleton is an important component in the plant defense mechanisms against attacks of pathogenic organisms. Plants however, are defenseless against parasitic root-knot and cyst nematodes and respond to the invasion by the development of a special feeding site that supplies parasite with nutrients required for the completion of its lifecycle. Surprisingly, recent analysis of the nematode invasion under treatment with cytoskeletal drugs and in the mutant plants, where normal functions of the cytoskeleton have been affected, demonstrates importance of the cytoskeleton in the establishment of the feeding site and successful nematode reproduction. It appears that in case of microfilaments, nematode hijacks the intracellular machinery that regulates actin dynamics and modulates organization and properties of the actin filament network. Intervention with this process reduces the infection efficiency and inhibits parasite’s life cycle. This discovery uncovers a new pathway that can be exploited for the protection of plants against nematodes.




REVIEWS

Open Access Article

APC-targeted RAA1 degradation mediates the cell cycle and root development in plants

Yunyuan Xu, Hong Cao and Kang Chong
Pages 218 - 223
http://dx.doi.org/10.4161/psb.5.3.10661
Abstract | PDF

Protein degradation by the ubiquitin–proteasome system is necessary for a normal cell cycle. As compared with knowledge of the mechanism in animals and yeast, that is less known in plants. Here we summarize research into the regulatory mechanism of protein degradation in the cell cycle in plants. Anaphase-promoting complex/cyclosome (APC), in the E3 family of enzymes, plays an important role in maintaining normal mitosis. APC activation and substrate specificity is determined by its activators, which can recognize the destruction box (D-box) in APC target proteins. Oryza sativa root architecture-associated 1 (OsRAA1) with GTP-binding activity was originally cloned from rice. Overexpression of of OsRAA1 inhibits the growth of primary roots in rice. Knockdown lines showed reduced height of seedlings because of abnormal cell division. OsRAA1 transgenic rice and fission yeast show a higher proportion of metaphase cells than that of controls, which suggests a blocked transition from metaphase to anaphase during mitosis. OsRAA1 co-localizes with spindle tubulin. It contains the D-box motif and interacts with OsRPT4 of the regulatory particle of 26S proteasome. OsRAA1 may be a cell cycle inhibitor that can be degraded by the ubiquitin–proteasome system, and its disruption is necessary for the transition from metaphase to anaphase during root growth in rice.

Open Access Article

Gibberellic acid and cGMP-dependent transcriptional regulation in Arabidopsis thaliana

René Bastian, Adam Dawe, Stuart Meier, Ndiko Ludidi, Vladimir B. Bajic and Chris Gehring
Pages 224 - 232
http://dx.doi.org/10.4161/psb.5.3.10718
Abstract | PDF

An ever increasing amount of transcriptomic data and analysis tools provide novel insight into complex responses of biological systems. Given these resources we have undertaken to review aspects of transcriptional regulation in response to the plant hormone gibberellic acid (GA) and its second messenger guanosine 3’,5’-cyclic monophosphate (cGMP) in Arabidopsis thaliana, both wild type and selected mutants. Evidence suggests enrichment of GA-responsive (GARE) elements in promoters of genes that are transcriptionally up-regulated in response to cGMP but down-regulated in a GA insensitive mutant (ga1-3). In contrast, in the genes up-regulated in the mutant, no enrichment in the GARE is observed suggesting that GARE elements are diagnostic for GA-induced and cGMP-dependent transcriptional up-regulation. Further, we review how expression studies of GA-dependent transcription factors and transcriptional networks based on common promoter signatures derived from ab initio analyses can contribute to our understanding of plant responses at the systems level.

Open Access Article

Cytosolic calcium and pH signaling in plants under salinity stress

Md Abdul Kader and Sylvia Lindberg
Pages 233 - 238
http://dx.doi.org/10.4161/psb.5.3.10740
Abstract | PDF

Calcium is one of the essential nutrients for growth and development of plants. It is an important component of various structures in cell wall and membranes. Besides some fundamental roles under normal condition, calcium functions as a major secondary-messenger molecule in plants under different developmental cues and various stress conditions including salinity stress. Also changes in cytosolic pH, pH_cyt, either individually, or in coordination with changes in cytosolic Ca²⁺ concentration, [Ca²⁺]_cyt, evoke a wide range of cellular functions in plants including signal transduction in plant-defense responses against stresses. It is believed that salinity stress, like other stresses, is perceived at cell membrane, either extra cellular or intracellular, which then triggers an intracellular-signaling cascade including the generation of secondary messenger molecules like Ca²⁺ and protons. The variety and complexity of Ca²⁺ and pH signaling result from the nature of the stresses as well as the tolerance level of the plant species against that specific stress. The nature of changes in [Ca²⁺]_cyt concentration, in terms of amplitude, frequency and duration, is likely very important for decoding the specific downstream responses for salinity stress tolerance in planta. It has been observed that the signatures of [Ca²⁺]_cyt and pH differ in various studies reported so far depending on the techniques used to measure them, and also depending on the plant organs where they are measured, such as root, shoot tissues or cells. This review describes the recent advances about the changes in [Ca²⁺]_cyt and pH_cyt at both cellular and whole-plant levels under salinity stress condition, and in various salinity-tolerant and -sensitive plant species.




RESEARCH PAPER

Open Access Article

Stimulation or inhibition: Conflicting evidence for (±)-catechin’s role as a chemical facilitator and disease protecting agent

Harsh P. Bais, L Venkatachalam and Meredith L. Biedrzycki
Pages 239 - 246
http://dx.doi.org/10.4161/psb.5.3.10573
Abstract | PDF

The occurrence of plant hormesis is poorly understood phenomenon, wherein low doses of phytotoxins unusually promote growth responses in higher plants. In contrast, negative plant-plant interactions mediated through secreted small molecular weight compounds initiate growth inhibitory responses. Studies related to (±)-catechin mediated allelopathy has transpired both novel information and generated significant controversy. Specifically, studies related to the phytotoxicity responses mediated by (±)-catechins have been seriously debated. The pronged opinion that (±)-catechin is phytotoxic versus non-phytotoxic relies more on the target plant systems and the conditions used to test phytotoxic responses. It is reported that lower than MIC dosage supplementation of (±)-catechin could promote growth responses in the model plant Arabidopsis thaliana. Furthermore, it was shown that sub-MIC levels of (±)-catechin supplementation leads to elicitation of disease resistance against Pseudomonas syringae DC3000 (hereafter DC3000). Intrigued by the unique hormesis response observed, we tested whether (±)-catechin indeed promotes growth responses in A. thaliana. In our hands, we observed no growth promotion responses of (±)-catechin against A. thaliana under in vitro or in soil. We also evaluated the previously reported disease protecting properties of (±)-catechin in A. thaliana against DC3000. The systematic observations to evaluate disease protecting properties entailing colony counts, disease incidences and loss of chlorophyll studies showed no disease protecting properties of (±)-catechin. The transcriptional response for a marker pathogenesis related PR1 defense gene showed no induction post (±)-catechin supplementation. The cell death genes (ACD2 and CAD1) associated with programmed cell death revealed unchanged expression levels in plants treated with sub-MIC levels of (±)-catechin. Further, we report supplementation of sub-MIC levels of (±)-catechin negates any change in the expression of an auxin responsive gene. Our results refute the previous claims of growth and defense inducing effects of (±)-catechin, thus suggesting that a thorough reexamination is required to evaluate the hormetic effect of (±)-catechin under both controlled and natural conditions.




ARTICLE ADDENDA

Open Access Article

The hunt for hypoxia responsive natural antisense short interfering RNAs

Dov Moldovan, Andrew Spriggs, Elizabeth S. Dennis and Iain W. Wilson
Pages 247 - 251
http://dx.doi.org/10.4161/psb.5.3.10548
Abstract | PDF

Small ribonucleic acids (smRNA) have been identified as important post-transcriptional regulators of gene expression. One important class of smRNA implicated in stress responses are natural antisense short interfering RNA (natsiRNA). These natsiRNAs are generated from two overlapping mRNA that are processed into short-interfering RNAs and target complementary mRNA sequences for degradation. A feature of natsiRNA is the inverse regulation of gene expression that is observed after environmental or developmental stimuli. Genome-wide expression analysis of hypoxia treated Arabidopsis roots in combination with the examination of gene expression in plants defective in natsiRNA processing, was used to find putative natsiRNA regulated genes. The results indicate the potential involvement of natsiRNA in regulating lipid signalling in hypoxia.

Open Access Article

Mechanisms of microRNA-mediated auxin signaling inferred from the rice mutant osaxr

Yijun Meng, Dijun Chen, Xiaoxia Ma, Chuanzao Mao, Junjie Cao, Ping Wu and Ming Chen
Pages 252 - 254
http://dx.doi.org/10.4161/psb.5.3.10549
Abstract | PDF

Auxin, known as the central hormone, plays essential roles in plant growth and development. In auxin signaling pathways, the tiny RNA molecules, i.e. microRNAs (miRNAs), show their strong potential in modulating the auxin signal transduction. Recently, we isolated a novel auxin resistant rice mutant osaxr (Oryza sativa auxin resistant) that exhibited plethoric root defects. Microarray experiments were carried out to investigate the expression patterns of both the miRNAs and the protein-coding genes in osaxr. A number of miRNAs showed reduced auxin sensitivity in osaxr compared with the wild type (WT), which may contribute to the auxin-resistant phenotype of the mutant. Auxin response elements (AuxREs) were demonstrated to be more frequently present in the promoters of auxin-related miRNAs. In our previous report, a comparative analysis of miRNA and protein-coding gene expression datasets uncovered a number of reciprocally expressed miRNA–target pairs. A feedback circuit between miRNA and auxin response factor (ARF) was then proposed. Here, we will discuss in-depth some points raised in the previous report, in particular, the organ-specific expression patterns of miR164, the feedback regulatory model between miR167 and certain ARFs, and the potential signal interactions between auxin and nutrition or stress that are mediated by miRNAs in rice roots.

Open Access Article

Identification and prediction of abiotic stress responsive transcription factors involved in abiotic stress signaling in soybean

Lam-Son Phan Tran and Keiichi Mochida
Pages 255 - 257
http://dx.doi.org/10.4161/psb.5.3.10550
Abstract | PDF

Abiotic stresses such as extreme temperature, drought, high salinity, cold and waterlogging often result in significant losses to the yields of economically important crops such as soybean (Glycine max L.). Transcription factors (TFs) which bind to DNA through specific cis-regulatory sequences either activate or repress gene transcription have been reported to act as control switches in stress signaling. Recent completion of the soybean genomic sequence has open wide opportunities for large-scale identification and annotations of regulatory TFs in soybean for functional studies. Within the soybean genome, we identified 5035 TF models which grouped into 61 families. Detailed annotations of soybean TF genes can be accessed at SoybeanTFDB (http://soybeantfdb.psc.riken.jp). Moreover, we have reported a new idea of high throughput prediction and selection of abiotic stress responsive TFs based on the existence of known stress responsive cis-element(s) located in the promoter regions of respective TFs and GO annotations. We, therefore, have provided a basic platform for the genome-wide analysis of regulatory mechanisms underlying abiotic stress responses and a reliable tool for prediction and selection of stress responsive TFs for further functional studies and genetic engineering.

Open Access Article

Sterol biosynthesis in oomycete pathogens

Elodie Gaulin, Arnaud Bottin and Bernard Dumas
Pages 258 - 260
http://dx.doi.org/10.4161/psb.5.3.10551
Abstract | PDF

Oomycetes are a diverse group of filamentous eukaryotic microbes comprising devastating animal and plant pathogens. They share many characteristics with fungi, including polarized hyphal extension and production of spores but phylogenetics studies have clearly placed oomycetes outside the fungal kingdom, in the kingdom Stramenopila which also includes marine organisms such diatoms and brown algae. Oomycetes display various specific biochemical features, including sterol metabolism. Sterols are essential isoprenoid compounds involved in membrane function and hormone signaling. Oomycetes belonging to Peronosporales, such as Phytophthora sp., are unable to synthesize their own sterols and must acquire them from their plant or animal hosts. In contrast, a combination of biochemical and molecular approaches allowed us to decipher a nearly complete sterol biosynthetic pathway leading to fucosterol in the legume pathogen Aphanomyces euteiches, an oomycete belonging to Sparolegniales. Importantly, sterol demethylase, a key enzyme from this pathway, is susceptible to chemicals widely used in agriculture and medicine as antifungal drugs suggesting that similar products could be used against plant and animal diseases caused by Saprolegniales.

Open Access Article

High-throughput transient transformation of Arabidopsis roots enables systematic colocalization analysis of GFP-tagged proteins

Bram Van Loock, Marios Nektarios Markakis, Jean-Pierre Verbelen and Kris Vissenberg
Pages 261 - 263
http://dx.doi.org/10.4161/psb.5.3.10575
Abstract | PDF

Determination of the subcellular localization of an unknown protein is a major step towards the elucidation of its function. Lately, the expression of proteins fused to fluorescent markers has been very popular and many approaches have been proposed to express these proteins. Stable transformation using Agrobacterium tumefaciens generates stable lines for downstream experiments, but is time-consuming. If only colocalisation is required, transient techniques save time and effort. Several methods for transient assays have been described including protoplast transfection, biolistic bombardment, Agrobacterium tumefaciens cocultivation and infiltration. In general colocalizations are preferentially performed in intact tissues of the same species, resembling the native situation. High transformation rates were described for cotyledons of Arabidopsis, but never for roots. Here we report that it is possible to transform Arabidopsis root epidermal cells with an efficiency that is sufficient for colocalization purposes.

Open Access Article

Reactive oxygen species derived from impaired quality control of Photosystem II are irrelevant to plasma-membrane NADPH oxidases

Eiko Miura, Yusuke Kato and Wataru Sakamoto
Pages 264 - 266
http://dx.doi.org/10.4161/psb.5.3.10604
Abstract | PDF

Protein quality control plays an important role in the photosynthetic apparatus because its components receive excess light energy and are susceptible to photooxidative damage. In chloroplasts, photodamage is targeted to the D1 protein of Photosystem II (PSII). The coordinated PSII repair cycle (PSII disassembly, D1 degradation and synthesis, and PSII reassembly) is necessary to mitigate photoinhibition. A thylakoid protease FtsH, which is formed predominantly as a heteromeric complex with two isoforms of FtsH2 and FtsH5 in Arabidopsis, is the major protease involved in PSII repair. A mutant lacking FtsH2 (termed var2) shows compromised D1 degradation. Furthermore, var2 accumulates high levels of chloroplastic reactive oxygen species (cpROS), reflecting photooxidative stress without functional PSII repair. To examine if the cpROS produced in var2 are connected to a ROS signaling pathway mediated by plasma membrane NADPH oxidase (encoded by AtRbohD or AtRbohF), we generated mutants in which either Rboh gene was inactivated under var2 background. Lack of NADPH oxidases had little or no impact on cpROS accumulation. It seems unlikely that cpROS in var2 activate plasma membrane NADPH oxidases to enhance ROS production and the signaling pathway. Mutants that are defective in PSII repair might be valuable for investigating cpROS and their physiological roles.

Open Access Article

Small and remarkable: The Micro-Tom model system as a tool to discover novel hormonal functions and interactions

Marcelo Lattarulo Campos, Rogério Falleiros Carvalho, Vagner Augusto Benedito and Lázaro Eustáquio Pereira Peres
Pages 267 - 270
http://dx.doi.org/10.4161/psb.5.3.10622
Abstract | PDF

Hormones are molecules involved in virtually every step of plant development and studies in this field have been shaping plant physiology for more than a century. The model plant Arabidopsis thaliana, long used as a tool to study plant hormones, lacks significant important developmental traits, such as fleshy climacteric fruit, compound leaf and multicellular trichomes, suggesting the necessity for alternative plant models. An attractive option often used is tomato, a species also of major economic importance, being ideal to bring together basic and applied plant sciences. The tomato Micro-Tom (MT) cultivar makes it possible to combine the direct benefits of studying a crop species with the fast life cycle and small size required for a suitable biological model. However, few obscure questions are constantly addressed to MT, creating a process herein called “MT mystification”. In this work we present evidence clarifying these questions and show the potential of MT, aiming to demystify it. To corroborate our ideas we showed that, by making use of MT, our laboratory demonstrated straightforwardly new hormonal functions and also characterized a novel antagonistic hormonal interaction between jasmonates and brassinosteroids in the formation of anti-herbivory traits in tomato.

Open Access Article

Increasing insight into induced plant defense mechanisms using elicitors and inhibitors

Maaike Bruinsma, Joop J.A. van Loon and Marcel Dicke
Pages 271 - 274
http://dx.doi.org/10.4161/psb.5.3.10623
Abstract | PDF

One of the strategies that plants employ to defend themselves against herbivore attack is the induced production of carnivore-attracting volatiles. Using elicitors and inhibitors of different steps of the signal-transduction pathways can improve our understanding of the mechanisms underlying induced plant defenses. For instance, we recently showed that application of jasmonic acid, a key hormone in the octadecanoid pathway involved in herbivore-induced defense, to Brassica oleracea affects gene expression, hormone levels and volatile emission, as well as oviposition by herbivores and host location behavior by parasitoids. Such defense responses vary with the dose of the elicitor and with time since application. This addendum describes how the use of inhibitors, in addition to the use of elicitors like jasmonic acid, can be applied in bio-assays to investigate the role of signal-transduction pathways involved in induced plant defense. We show how inhibition of different steps of the octadecanoid pathway affects host location behavior by parasitoids.

Open Access Article

Specific developmental pathways underlie host specificity in the parasitic plant Orobanche

Chris Thorogood and Simon Hiscock
Pages 275 - 277
http://dx.doi.org/10.4161/psb.5.3.10660
Abstract | PDF

Parasitic angiosperms are an ecologically and economically important group of plants. However our understanding of the basis for host specificity in these plants is embryonic. Recently we investigated host specificity in the parasitic angiosperm Orobanche minor, and demonstrated that this host generalist parasite comprises genetically defined races that are physiologically adapted to specific hosts. Populations occurring naturally on red clover (Trifolium pratense) and sea carrot (Daucus carota subsp. gummifer) respectively, showed distinct patterns of host specificity at various developmental stages, and a higher fitness on their natural hosts, suggesting these races are locally adapted. Here we discuss the implications of our findings from a broader perspective. We suggest that differences in signal responsiveness and perception by the parasite, as well as qualitative differences in signal production by the host, may elicit host specificity in this parasitic plant. Together with our earlier demonstration that these O. minor races are genetically distinct based on molecular markers, our recent data provide a snapshot of speciation in action, driven by host specificity. Indeed, host specificity may be an underestimated catalyst for speciation in parasitic plants generally. We propose that identifying host specific races using physiological techniques will complement conventional molecular marker-based approaches to provide a framework for delineating evolutionary relationships among cryptic host-specific parasitic plants.

Open Access Article

BASL and EPF2 act independently to regulate asymmetric divisions during stomatal development

Lee Hunt and Julie E Gray
Pages 278 - 280
http://dx.doi.org/10.4161/psb.5.3.10704
Abstract | PDF

The initiation of stomatal development in the developing Arabidopsis epidermis is characterized by an asymmetric ‘entry’ division in which a small cell, known as a meristemoid, and a larger daughter cell is formed. The meristemoid may undergo further asymmetric divisions, regenerating a meristemoid each time, before differentiating into a guard mother cell which divides symmetrically to form a pair of guard cells surrounding a stomatal pore. Recently EPF2 and BASL have emerged as regulators of these asymmetric divisions and here we present results indicating that these two factors operate independently to control stomatal development.

Open Access Article

Cutting to the base: Identifying regulators of adventitious rooting

Gustavo A. Ramirez-Carvajal and John M. Davis
Pages 281 - 283
http://dx.doi.org/10.4161/psb.5.3.10705
Abstract | PDF

Adventitious roots are distinct from primary and lateral roots in that adventitious roots develop ectopically from aboveground organs. Whole-genome microarrays in poplar provided the first glimpse into the gene networks that are remodeled in cells prior to the development of adventitious roots. In the first 24 hr after removal of stem cuttings, over one-half of the transcripts encoded in the genome showed evidence of differential abundance in the cells that will eventually give rise to adventitious roots. Major processes that were regulated appear related to physiological adaptation of the cutting to acute loss of water and nutrients as well as hormone signaling. Comparative transcriptome analysis of genotypes that differ in their competence to form adventitious roots may be a generally useful strategy to identify genes that regulate adventitious rooting efficiency.

Open Access Article

ERECTA controls low light intensity-induced differential petiole growth independent of Phytochrome B and Cryptochrome 2 action in Arabidopsis thaliana

Martijn van Zanten, L. Basten Snoek, Evelien van Eck-Stouten, Marcel C.G. Proveniers, Keiko U. Torii, Laurentius A.C.J. Voesenek, Frank F. Millenaar and Anton J.M. Peeters
Pages 284 - 286
http://dx.doi.org/10.4161/psb.5.3.10706
Abstract | PDF

Plants can respond quickly and profoundly to changes in their environment. Several species, including Arabidopsis thaliana, are capable of differential petiole growth driven upward leaf movement (hyponastic growth) to escape from detrimental environmental conditions. Recently, we demonstrated that the leucine-rich repeat receptor-like Ser/Thr kinase gene ERECTA, explains a major effect Quantitative Trait Locus (QTL) for ethylene-induced hyponastic growth in Arabidopsis. Here, we demonstrate that ERECTA controls the hyponastic growth response to low light intensity treatment in a genetic background dependent manner. Moreover, we show that ERECTA affects low light-induced hyponastic growth independent of Phytochrome B and Cryptochrome 2 signaling, despite that these photoreceptors are positive regulators of low light-induced hyponastic growth.

Open Access Article

New insights into the early biochemical activation of jasmonic acid biosynthesis in leaves

Gustavo Bonaventure and Ian T. Baldwin
Pages 287 - 289
http://dx.doi.org/10.4161/psb.5.3.10713
Abstract | PDF

In plants, herbivore attack elicits the rapid accumulation of jasmonic acid (JA) which results from the activation of constitutively expressed biosynthetic enzymes. The molecular mechanisms controlling the activation of JA biosynthesis remain largely unknown however new research has elucidated some of the early regulatory components involved in this process. Nicotiana attenuata plants, a wild tobacco species, responds to fatty acid amino acid conjuguates (FAC) elicitors in the oral secretion of its natural herbivore, Manduca sexta, by triggering specific defense and tolerance responses against it; all of the defense responses known to date require the amplification of the wound-induced JA increase. We recently demonstrated that this FAC-elicited JA burst requires an increased flux of free linolenic acid (18:3) likely originating from the activation of a plastidial glycerolipase (GLA1) which is activated by an abundant FAC found in insect oral secretions, N-linolenoyl-glutamate (18:3-Glu). The lack of accumulation of free 18:3 after elicitation suggests a tight physical association between GLA1 and LOX3 in N. attenuata leaves. In addition, the salicylate-induced protein kinase (SIPK) and the nonexpressor of PR-1 (NPR1) participate in this activation mechanism that controls the supply of 18:3. In contrast, the wound-induced protein kinase (WIPK) does not but instead regulates the conversion of 13(S)-hydroperoxy-18:3 into 12-oxo-phytodienoic acid (OPDA). These results open new perspectives on the complex network of signals and regulatory components inducing the JA biosynthetic pathway.

Open Access Article

Root growth is affected differently by mechanical wounding in seedlings of the ecological model species Nicotiana attenuata and the molecular model species Arabidopsis thaliana

Lilian Schmidt and Achim Walter
Pages 290 - 292
http://dx.doi.org/10.4161/psb.5.3.10719
Abstract | PDF

In the ecological model plant Nicotiana attenuata, leaf wounding or herbivory lead to a reduction of root growth via jasmonic acid (JA) signalling. A single wounding treatment is sufficient to induce this response; multiple wounding does not increase the plant growth reaction. In a recent study, in which JA bursts were elicited in leaves of the molecular model species Arabidopsis thaliana in different ways (1), we tested whether JA induces the same response there. Root growth reduction was neither induced by foliar application of herbivore oral secretions nor by direct application of methyl jasmonate to leaves. Root growth reduction was observed when leaves were infected with the pathogen Pseudomonas syringae pv. tomato, which persistently induces the JA signaling pathway. Yet, growth analyses of this effect in wild type and JA-signaling mutants showed that it was elicited by the bacterial toxin coronatine which suggests ethylene- but not JA-induced root growth reduction in A. thaliana. Moreover, the growth effects were somewhat masked by a light-induced diurnal decrease of root growth. Overall, we conclude that the reaction of root growth to herbivore-induced JA signaling differs among species, which is related to different ecological defence strategies that have evolved in different species.

Open Access Article

Thalloid organisms and the fossil record: New perspectives from the Transantarctic Mountains

Benjamin Bomfleur, Michael Krings and Hans Kerp
Pages 293 - 295
http://dx.doi.org/10.4161/psb.5.3.10736
Abstract | PDF

Thalloid body plans occur in several groups of organisms, including bryophytes, lichens and algae. While many aspects of the biology and ecology of extant thalloid organisms are well understood today, knowledge about the evolutionary history, palaeobiology and palaeoecology of these life forms remains limited. The recently discovered thalloid fossil Litothallus ganovex from the Triassic of Antarctica consists of fused vertical cell filaments forming a pseudoparenchymatous crust-like body, and most likely represents a freshwater macroalga. Other cuticle fragments from Antarctica are tentatively interpreted as remains of thallose liverworts. These unexpected new finds indicate that thalloid organisms are more frequent in the fossil record than previously assumed and contribute to a better understanding of the palaeobiodiversity of ancient non-marine ecosystems.

Open Access Article

Overexpression of the CBF2 transcriptional activator in Arabidopsis counteracts hormone activation of leaf senescence

Michal Sharabi-Schwager, Alon Samach and Ron Porat
Pages 296 - 299
http://dx.doi.org/10.4161/psb.5.3.10739
Abstract | PDF

CBF1-3 (C-repeat binding factors) are transcriptional activators governing plant responses to low temperatures. Overexpression of CBF1-3 genes enhances plant frost tolerance, but also causes various pleiotropic effects regarding plant growth and development, mainly growth retardation and delay of flowering and senescence. In a recent study, we reported that overexpression of CBF2 suppressed leaf senescence induced by the stress hormone ethylene. Here we show that overexpression of CBF2 also suppressed chlorophyll breakdown and leaf senescence induced by the phytohormones abscisic acid (ABA), salicylic acid (SA) and methyl jasmonate (MeJA), which indicates its broader role in suppressing hormone-induced leaf senescence. As previously reported for ethylene, the observed decrease in responsiveness to ABA in CBF2-overexpressing plants was specific to leaf senescence, since other responses to ABA were similar to those of wild-type plants. Transcript profiling analysis of hormone metabolism and responsive genes revealed that overexpression of CBF2 induced expression of ABA-biosynthesis and ABA-responsive genes and suppressed SA- and JA-related genes. Overall, in light of the adverse effects of CBF2 on ABA metabolism and responsiveness, on the one hand, and SA and JA metabolism and responsiveness, on the other hand, we conclude that overexpression of CBF2 suppresses hormone-induced leaf senescence by directly counteracting the hormone effects on leaf senescence and not by general suppression of their synthesis or signal transduction pathways.

Open Access Article

Multiple receptor complexes assembled for transmitting CLV3 signaling in Arabidopsis

Yingfang Zhu, Yinglang Wan and Jinxing Lin
Pages 300 - 302
http://dx.doi.org/10.4161/psb.5.3.10790
Abstract | PDF

In Arabidopsis, the feedback regulatory loop between CLAVATA3 (CLV3) signaling pathway and transcription factor, WUSCHEL (WUS) plays a significant role in shoot apical meristems (SAM) maintenance. Previously, CLV1/CLV2 heterodimers were supposed to perceive and transmit CLV3 signaling. Recent genetic analysis isolated a novel receptor kinase, CORYNE (CRN), which was found to be involved in the CLV3 pathway. Therefore, new hypothesis was put forward that CRN probably acts with CLV2 to transmit CLV3 in parallel with CLV1 based on genetic analysis. In our recent work, we took advantage of firefly luciferase complementation imaging (LCI) assay to analyze the interactions among CLV1, CLV2 and CRN in both Arabidopsis thaliana protoplasts and Nicotiana benthamiana leaves. We identified the physical interaction between CLV2 and CRN in the absence of CLV3 and found some interesting phenomenon such as CLV1, CLV2, and CRN may form a complex, and that CRN was able to form homodimers. These new observations make the relationships among these three proteins more complex than that indicated in two-parallel pathway model. Combining current genetic and our new biochemical evidence, a more possible and detailed model for CLV3 pathway was developed.

Open Access Article

Is annexin 1 a multifunctional protein during stress responses?

Greg Clark, Dorota Konopka-Postupolska, Jacek Hennig and Stanley Roux
Pages 303 - 307
http://dx.doi.org/10.4161/psb.5.3.10835
Abstract | PDF

Accumulating evidence suggest that certain annexins can play a role in abiotic stress responses in plants. We found that for one member of the Arabidopsis annexin gene family, annexin 1 (AnnAt1), loss-of-function mutants are more sensitive to drought stress and gain-of-function mutants are more tolerant1. We also found that AnnAt1 is able to regulate accumulation of H₂O₂ in vivo in Arabidopsis cells based on the observation that the level of ROS accumulation following induction by ABA correlates with the level of AnnAt1 protein in transgenic Arabidopsis plants. Here we provide more commentary on the antioxidant activity of AnnAt1, critically assess the evidence that AnnAt1 and other annexins possess peroxidase activity, emphasize a redox-induced post-translational modification which occurs to AnnAt1 during ABA signaling, and discuss ways this annexin’s membrane associations could mediate stress signaling while addressing the potential that AnnAt1 is a multifunctional protein in plants.

Open Access Article

Polyamines and jasmonic acid induce plasma membrane potential variations in Lima bean

Rika Ozawa, Cinzia M. Bertea, Maria Foti, Ravishankar Ravishankar Narayana, Gen-Ichiro Arimura, Atsushi Muroi, Massimo E. Maffei and Junji Takabayashi
Pages 308 - 310
http://dx.doi.org/10.4161/psb.5.3.10848
Abstract | PDF

Exogenous polyamines (PAs) [cadaverine (Cad), putrescine (Put), spermidine (Spd) and spermine (Spm)] elicit the production of volatiles in Lima bean (Phaseolus lunatus). Among the tested PAs, Spm induces of the production of some volatile terpenoids that are known to be induced by the spider mite Tetranychus urticae. Spm treatment elicits the biosynthesis of Jasmonic acid (JA), a phytohormone known to regulate the production of the volatile terpenoids. The treatment with JA together with Spm resulted in the increased volatile emission, and predatory mites Phytoseiulus persimilis preferred JA and Spm-treated leaves over those treated with JA alone.⁵ JA and Spm treatment has no effects on polyamine oxidase (PAO) and Cu-amine oxidase (CuAO) but has a significant induction of calcium influx, ROS production, enzyme activities for NADPH-oxidase complex, superoxide dismutase, catalase, ascorbate peroxidase, glutathione reductase and glutathione peroxidase, and gene expressions except for NADPH-oxidase complex. ⁵ Here, we report that a plasma membrane potential (V_m) depolarization was observed after polyamine perfusion with an increasing trend: Spm, Cad, Put and Spd. JA perfusion did not alter V_m but the perfusion of JA and the polyamines significantly increased Cad and Put V_m depolarization. When JA was perfused with polyamines, a negative correlation was found between V_m depolarization and the number of amino group of the polyamines tested.

Open Access Article

Sugar signaling of fructan metabolism: New insights on protein phosphatases in sucrose-fed wheat leaves

Giselle Martinez-Noel, Jorge A. Tognetti, Graciela Salerno and Pontis Horacio
Pages 311 - 313
http://dx.doi.org/10.4161/psb.5.3.10924
Abstract | PDF

Protein phosphatase type 2A (PP2A) activity is required for the sucrose induction of fructan metabolism in wheat leaves, as shown in experiments with the addition of the specific inhibitor okadaic acid (OA) together with sucrose. However, a decrease in total PP2A activity has been found along sucrose treatment. Here we analyze the effect of sucrose feeding to wheat leaves on PP2A activity profiles after Deae-Sephacel and Superose separation, in comparison with those of control leaves. The results show no evidence of changes in PP2A activity profiles as a consequence of sucrose feeding. In all, our data suggest that constitutive levels of PP2A activity may be sufficient for the sucrose-mediated induction of fructan metabolism and that general decrease of PP2A activity produced by long-term treatment with sucrose may be due to a negative feedback regulation.

Open Access Article

Nitric oxide modulates sensitivity to ABA

Jorge Lozano-Juste and José León
Pages 314 - 316
http://dx.doi.org/10.4161/psb.5.3.11235
Abstract | PDF

Nitric oxide (NO) is a gas with crucial signaling functions in plant defence and development. As demonstrated by generating a triple nia1nia2noa1-2 mutant with extremely low levels of NO (February 2010 issue of Plant Physiology), NO is synthesized in plants through mainly two different pathways involving nitrate reductase (NR/NIA) and NO Associated 1 (AtNOA1) proteins. Depletion of basal NO levels leads to a priming of ABA-triggered responses that causes hypersensitivity to this hormone and results in enhanced seed dormancy and decreased seed germination and seedling establishment in the triple mutant. NO produced under non-stressed conditions represses inhibition of seed developmental transitions by ABA. Moreover, NO plays a positive role in post-germinative vegetative development and also exerts a critical control of ABA-related functions on stomata closure. The triple nia1nia2noa1-2 mutant is hypersensitive to ABA in stomatal closure thus resulting in a extreme phenotype of resistance to drought. In the light of the recent discovery of PYR/PYL/RCAR as a family of potential ABA receptors, regulation of ABA sensitivity by NO may be exerted either directly on ABA receptors or on downstream signalling components; both two aspects that deserve our present and future attention.

Open Access Article

Vegetative axillary bud dormancy induced by shade and defoliation signals in the grasses

Tesfamichael H Kebrom, Thomas P Brutnell, Dirk B Hays and Scott A Finlayson
Pages 317 - 319
http://dx.doi.org/10.4161/psb.5.3.11186
Abstract | PDF

Vegetative axillary bud dormancy and outgrowth is regulated by several hormonal and environmental signals. In perennials, the dormancy induced by hormonal and environmental signals has been categorized as eco-, endo- or para-dormancy. Over the past several decades para-dormancy has primarily been investigated in eudicot annuals. Recently, we initiated a study using the monoculm phyB mutant (phyB-1) and the freely branching near isogenic wild type (WT) sorghum (Sorghum bicolor) to identify molecular mechanisms and signaling pathways regulating dormancy and outgrowth of axillary buds in the grasses. In a paper published in the January 2010 issue of Plant Cell and Environment, we reported the role of branching genes in the inhibition of bud outgrowth by phyB, shade and defoliation signals. Here we present a model that depicts the molecular mechanisms and pathways regulating axillary bud dormancy induced by shade and defoliation signals in the grasses.

Open Access Article

The Arabidopsis translatome cell-specific mRNA atlas: Mining suberin and cutin lipid monomer biosynthesis genes as an example for data application

Angelika Mustroph and Julia Bailey-Serres
Pages 320 - 324
http://dx.doi.org/10.4161/psb.5.3.11187
Abstract | PDF

Plants consist of numerous cell types distinguished by position, morphological features, and metabolic activities. We recently developed a method to extract cell-type specific mRNA populations by immunopurification of ribosome-associated mRNAs. Microarray profiles of 21 cell-specific mRNA populations from seedling roots and shoots comprise the Arabidopsis Translatome dataset. This gene expression atlas provides a new tool for the study of cell-specific processes. Here we provide an example of how genes involved in a pathway limited to one or few cell-types can be further characterized and new candidate genes can be predicted. Cells of the root endodermis produce suberin as an inner barrier between the cortex and stele, whereas the shoot epidermal cells form cutin as a barrier to the external environment. Both polymers consist of fatty acid derivates, and share biosynthetic origins. We use the Arabidopsis Translatome dataset to demonstrate the significant cell-specific expression patterns of genes involved in those biosynthetic processes and suggest new candidate genes in the biosynthesis of suberin and cutin.

Open Access Article

Arabidopsis SMO2 regulates seed germination and ABA response

Zhubing Hu, Xiaoran Zhang, Zhixiang Qin and Yuxin Hu
Pages 325 - 327
http://dx.doi.org/10.4161/psb.5.3.11189
Abstract | PDF

Arabidopsis SMALL ORGAN2 (SMO2) encodes a functional homologue of yeast TRM112, and disruption of Arabidopsis SMO2 results in a defect in progression of cell division and organ growth. Here, we show that SMO2 mediates the abscisic acid (ABA) response during seed germination. smo2 exhibits an obvious delay of seed germination and is hypersensitive to abscisic acid (ABA), while transgenic seeds overexpressing SMO2 are hyposensitive to ABA. Given that SMO2 is required for proper cell division in root apex, our observation suggests that SMO2-regulated progression of cell division is involved in ABA response during seed germination.

Open Access Article

Cleavage of a non-conserved target by a specific miR156 isoform in root apexes of medicago truncatula

Loreto Naya, Ghazanfar Abbas Khan, Céline Sorin, Caroline Hartmann, Martin Crespi and Christine Lelandais-Brière
Pages 328 - 331
http://dx.doi.org/10.4161/psb.5.3.11190
Abstract | PDF

Micro RNAs (miRNAs) have emerged as an important class of gene expression regulators controlling development, growth and metabolism. These short RNA molecules are 20–24 nucleotides in length and act post-transcriptionally to regulate the cleavage or translation of specific mRNA targets. In the model legume Medicago truncatula, we have recently reported identification of 100 novel and 27 conserved miRNAs in root apexes and nodules. Statistical analysis on sequencing results revealed specific miRNA isoforms for the same family (up to 3 mismatches) showing contrasting expression patterns between these tissues. Here, we report the cleavage of a non-conserved target of miR156 in root apexes complementary to a differentially expressed miR156 isoform. This suggests that changes in the abundance of miRNA isoforms may have functional consequences on the post-transcriptional regulation of new mRNA targets in different organs.

Open Access Article

Insights into the regulation of the core clock component TOC1 in the green picoeukaryote Ostreococcus

El Batoul Djouani-Tahri, Jean-Paul Motta, François-Yves Bouget and Florence Corellou
Pages 332 - 335
http://dx.doi.org/10.4161/psb.5.3.11212
Abstract | PDF

Living organisms such as plants and animals have evolved endogenous clocks in order to anticipate the environmental changes associated with the earth’s rotation and to orchestrate biological processes in the course of the 24 hour daily cycle. We have recently identified clock components in the primitive green picoalga Ostreococcus tauri, a promising minimal cellular and genomic model for systems biology approaches. A homologue of the Arabidopsis core clock gene Time of CAB expression-1 (TOC1) was shown to play a central role in Ostreococcus heralding an early emergence of clock components in the green lineage. Here we report the regulation of TOC1 at dusk in response to light and dark cues.