Table of Contents

Volume 3, Issue 8

  August 2008

  Pages 511 - 612

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MINI-REVIEWS

Open Access Article

14-3-3 Proteins, red light, and photoperiodic flowering: A point of connection?

Anna-Lisa Paul, Kevin M. Folta and Robert J. Ferl
Pages 511 - 515
http://dx.doi.org/10.4161/psb.3.8.5717
Abstract | PDF

The 14-3-3 family of proteins is well known for participating in signal transduction by binding specifically phosphorylated proteins, thereby completing their kinase-induced transition in activity or localization. This interaction-based modulation of signal flux through metabolic pathways is a critical feature of many important eukaryotic signal transduction cascades. Only recently, however, have studies in Arabidopsis thaliana described that some of the most fundamental plant signal transduction pathways, including the photoperiodic flowering pathway, are functionally affected by 14-3-3s. There are pivotal points in the photoperiod pathway that are characterized by the accumulation, localization and stability of critical protein factors, all of which are strongly affected by light quality and photoperiod duration. These mechanisms (localization, phosphorylation, regulated proteolysis) are the same as those regulated by 14-3-3 proteins in other systems. Yet it is only recently that well characterized 14-3-3 genetic tools have become available in sufficient diversity to make it possible to truly tie 14-3-3 interactions to light signaling and flowering. This review presents an overview of photoperiodic flowering signaling and direct 14-3-3 participation in the process, coupled with a discussion of the overlapping and specific roles of 14-3-3s which present confounding issues in the functional dissection of this family of signaling proteins.

Open Access Article

Responses and tolerance to salt stress in bryophytes

Xiaoqin Wang, Zheng Liu and Yikun He
Pages 516 - 518
http://dx.doi.org/10.4161/psb.3.8.6337
Abstract | PDF

During exposure to salt environments, plants could perceive salt signal and transmit the signal to cellular machinery to activate adaptive responses. In bryophytes, salt signal components and transcript factor identified suggest that salt activate adaptive responses to tolerate adverse environments. The ability of bryophytes to tolerate salt is determined by multiple biochemical pathways. Transmembrane transport proteins that mediate ion fluxes play a curial role in ionic and osmotic homeostasis under salt environments. Defense proteins protect cells from denaturation and degradation, as well as from oxidative damage following exposure to salt stress in bryophytes. ABA and salt stress positively affect the expression of common genes that participate in protection plant cells from injure, and ABA may be responsible for the ability to tolerate salt stress in bryophytes. In this paper, we reveal the mechanisms of salt responses and tolerance in bryophytes, and imply conservation between higher plants and bryophytes in response and tolerance to salt stress.

Open Access Article

Plants as green phone: Novel insights into plant-mediated communication between below- and aboveground insects

Roxina Soler, Jeffrey A. Harvey, T. Martijn Bezemer and Josef F. Stuefer
Pages 519 - 520
http://dx.doi.org/10.4161/psb.3.8.6338
Abstract | PDF

Plants can act as vertical communication channels or ‘green phones’ linking soil-dwelling insects and insects in the aboveground ecosystem. When root-feeding insects attack a plant, the direct defense system of the shoot is activated, leading to an accumulation of phytotoxins in the leaves. The protection of the plant shoot elicited by root damage can impair the survival, growth and development of aboveground insect herbivores, thereby creating plant-based functional links between soil-dwelling insects and insects that develop in the aboveground ecosystem. The interactions between spatially separated insects below- and aboveground are not restricted to root and foliar plant-feeding insects, but can be extended to higher trophic levels such as insect parasitoids. Here we discuss some implications of plants acting as communication channels or ‘green phones’ between root and foliar-feeding insects and their parasitoids, focusing on recent findings that plants attacked by root-feeding insects are significantly less attractive for the parasitoids of foliar-feeding insects.

Open Access Article

Critical consideration on the relationship between auxin transport and calcium transients in gravity perception of Arabidopsis seedlings

Masatsugu Toyota, Takuya Furuichi, Hitoshi Tatsumi and Masahiro Sokabe
Pages 521 - 524
http://dx.doi.org/10.4161/psb.3.8.6339
Abstract | PDF

Plants regulate their growth and morphogenesis in response to gravity field, known as gravitropism. In the early process of gravitropism, changes in the gravity vector (gravistimulation) are transduced into certain intracellular signals, termed gravity perception. The plant hormone auxin is not only a crucial factor to represent gravitropism but also a potential signaling molecule for gravity perception. Another strong candidate for the signaling molecule is calcium ion of which cytoplasmic concentration ([Ca2+]c) is known to increase in response to gravistimulation. However, relationship between these two factors, say which is in the first place, has been controversial. This issue is addressed here mainly based on recent progress including our latest studies. Gravistimulation by turning plants 180o induced a two-peaked [Ca2+]c-increase lasting for several minutes in Arabidopsis seedlings expressing apoaequorin; only the second peak was sensitive to the gravistimulation. Peak amplitudes of the [Ca²⁺]_c-increase were attenuated by the 10 µM auxin transport inhibitor (TIBA) and vesicle trafficking inhibitor (BFA), whereas the onset time and rate of rise of the second peak were not significantly altered. This result indicates that polar auxin transport is not involved in the initial phase of the second [Ca²⁺]_c-increase. It is likely that the gravi-induced [Ca²⁺]_c-increase constitutes an upstream event of the auxin transport, but may positively be modulated by auxin since its peak amplitude is attenuated by the inhibition of auxin transport.




REVIEW

Open Access Article

Chemical signaling under abiotic stress environment in plants

Narendra Tuteja and Sudhir K. Sopory
Pages 525 - 536
http://dx.doi.org/10.4161/psb.3.8.6186
Abstract | PDF

Many chemicals are critical for plant growth and development and play an important role in integrating various stress signals and controlling downstream stress responses by modulating gene expression machinery and regulating various transporters/pumps and biochemical reactions. These chemicals include calcium (Ca²⁺), cyclic nucleotides, polyphosphoinositides, nitric oxide (NO), sugars, abscisic acid (ABA), jasmonates (JA), salicylic acid (SA) and polyamines. Ca²⁺ is one of the very important ubiquitous second messengers in signal transduction pathways and usually its concentration increases in response to the stimuli including stress signals. Many Ca²⁺ sensors detect the Ca²⁺ signals and direct them to downstream signaling pathways by binding and activating diverse targets. cAMP or cGMP protects the cell with ion toxicity. Phosphoinositides are known to be involved both in transmission of signal across the plasma membrane and in intracellular signaling. NO activates various defense genes and acts as a developmental regulator in plants. Sugars affect the expression of many genes involved in photosynthesis, glycolysis, nitrogen metabolism, sucrose and starch metabolism, defense mechanisms and cell cycle regulation. ABA, JA, SA and polyamines are also involved in many stress responses. Cross-talk between these chemical signaling pathways is very common in plant responses to abiotic and bitotic factors. In this article we have described the role of these chemicals in initiating signaling under stress conditions mainly the abiotic stress.




RESEARCH PAPERS

Open Access Article

Arabidopsis GH3.5 regulates salicylic acid-dependent and both NPR1-dependent and independent defense responses

Zhongqin Zhang, Muyang Wang, Zhimiao Li, Qun Li and Zuhua He
Pages 537 - 542
http://dx.doi.org/10.4161/psb.3.8.5748
Abstract | PDF

The cross-talk between plant disease resistance and development is fundamental to understanding systemic physiological processes during pathogen attack. Our previous study showed that the Arabidopsis GH3.5 gene acts as a bifunctional modulator of the salicylic acid (SA)-mediated resistance and the auxin-mediated susceptibility during the Arabidopsis-Pseudomonas syringae interaction as well as development. Here, we further study the role and mechanism of GH3.5 involved in the SA-dependent defense pathway. Transcript and histochemical analysis of the GH3.5 promoter::GUS reporter expression indicate that GH3.5 is expressed with a strong temporal and spatial manner with predominant expression in the divisional tissues. Upon bacterial challenge, GUS activity is induced in the junction tissue around the infiltrated zone with higher levels in the vasculature with a pattern different between the incompatible and compatible interactions. Exogenous SA application enhances disease resistance in the activation-tagged mutant gh3.5-1D, while the GH3.5-mediated defense enhancement is depleted in the SA deficient gh3.5-1D/NahG double mutant, indicating that GH3.5 modulates defense response through the SA-dependent pathway. Furthermore, bacterial growth in the gh3.5-1D/npr1 double mutant treated with SA indicates that GH3.5 enhances the SA-mediated defense response through both NPR1-dependent and independent pathways.

Open Access Article

Towards a reporter system to identify regulators of cross-talk between salicylate and jasmonate signaling pathways in Arabidopsis

Annemart Koornneef, Adriaan Verhage, Antonio Leon-Reyes, Reinier Snetselaar, L.C. Van Loon and Corné M.J. Pieterse
Pages 543 - 546
http://dx.doi.org/10.4161/psb.3.8.6151
Abstract | PDF

The plant signaling hormones salicylic acid (SA) and jasmonic acid (JA) are regulators of inducible defenses that are activated upon pathogen or insect attack. Cross-talk between SA- and JA-dependent signaling pathways allows a plant to finely tune its response to the attacker encountered. In Arabidopsis, pharmacological experiments revealed that SA exerts a strong antagonistic effect on JA-responsive genes, such as PDF1.2, indicating that the SA pathway can be prioritized over the JA pathway. SA-mediated suppression of the JA-responsive PDF1.2 promoter was exploited for setting up a genetic screen aiming at the isolation of signal transduction mutants that are impaired in this cross-talk mechanism. The PDF1.2 promoter was fused to the herbicide resistance gene BAR to allow for life/death screening of a population of mutagenized transgenic plants. Non-mutant plants should survive herbicide treatment when methyl jasmonate (MeJA) is applied, but suppression of the JA response by SA should be lethal in combination with the herbicide. Conversely, crucial SA/JA cross-talk mutants should survive the combination treatment. SA effectively suppressed the expression of the PDF1.2::BAR transgene. However, suppression of the BAR gene did not result in suppression of herbicide resistance. Hence, a screening method based on quantitative differences in the expression of a reporter gene may be better suited to identify SA/JA cross-talk mutants. Here, we demonstrate that the PDF1.2::GUS reporter will be excellently suited in this respect.




ARTICLE ADDENDA

Open Access Article

STH2 has 2 B there: An insight into the role of B-box containing proteins in Arabidopsis

Sourav Datta, Henrik Johansson, Chamari Hettiarachchi and Magnus Holm
Pages 547 - 548
http://dx.doi.org/10.4161/psb.3.8.5695
Abstract | PDF

Recently we reported the identification of a novel B-box transcription factor SALT TOLERANCE HOMOLOG 2 (STH2) that interacts genetically with two key regulators of the light-signaling pathway, HY5 and COP1. We also provided phenotypic and genetic characterization of the sth2 mutant suggesting that STH2 plays a positive role in regulating photomorphogenesis both independently or together with HY5. Functional assays in protoplasts revealed that STH2 could act as a transcriptional activator. To our knowledge this is the first report of a B-box domain containing protein playing a direct role in activating transcription in plants. Here we discuss the possible position of STH2 in the transcriptional network and comment on the role of the B-box domain in plants.

Open Access Article

Cell-penetrating peptides: From mammalian to plant cells

François Eudes and Archana Chugh
Pages 549 - 550
http://dx.doi.org/10.4161/psb.3.8.5696
Abstract | PDF

Internalization of cell-penetrating peptides, well described in mammalian cell system, has recently been reported in a range of plant cells by three independent groups. Despite fundamental differences between animal cell and plant cell composition, the CPP uptake pattern between the mammalian system and the plant system is very similar. Tat, Tat-2 pVEC and transportan internalisation is concentration dependent and non saturable, enhanced at low temperature (4^oC), and receptor independent. The use of CPPs as nanocarrier for macromolecular delivery in plant cells is now achievable and the advances made in mammalian cells greatly enhance our understanding of cell-membrane and CPP-macromolecule complex interaction in plant. The cross membrane nanocarrier ability of CPPs promises new avenues in the field of plant biotechnology.

Open Access Article

Zmspds2 maize gene: Coding a spermine synthase?

Margarita Rodríguez-Kessler and Juan Francisco Jiménez-Bremont
Pages 551 - 553
http://dx.doi.org/10.4161/psb.3.8.5697
Abstract | PDF

During the last decade, growing evidence has arisen referring the importance of the proper regulation of plant polyamine metabolism in the response to stress conditions. Being the activation of signaling pathways, the stabilization of anionic molecules and prevention of their degradation, as well as the free radical scavenger properties of polyamines some possible mechanisms exerted by these amines. Accumulation of polyamines (putrescine, spermidine and spermine) has been associated to plant tolerance to a wide array of environmental stresses. The synthesis of spermidine and spermine is mediated by aminopropyltransferases (spermidine and spermine synthases) which constitute a class of widely distributed enzymes that use decarboxylated S-adenosylmethionine as an aminopropyl donor, and putrescine or spermidine as an amino acceptor. We recently reported the effect of salt stress on the expression of aminopropyltransferase genes in maize seedlings. Our data revealed a time and NaCl dependent regulation of the Zmspds2 and Zmspds1 genes, possibly mediated by abscisic acid, since these genes were regulated at the transcriptional level by this plant hormone. In this addendum, we show that the Zmspds2 gene initially classified as spermidine synthase might encode a spermine synthase based on an in silico analysis. This is discussed in terms of protein homologies and specific amino acid substitutions between aminopropyltransferase enzymes.

Open Access Article

Redrawing the borderline: Control of DNA replication at fertilization

Arnaud Ronceret and Martine Devic
Pages 554 - 555
http://dx.doi.org/10.4161/psb.3.8.5698
Abstract | PDF

In our recent paper in Plant Journal, we described the transcriptional activation of AtTMPK (thymidylate kinase), a recognized G1/S phase marker of the cell cycle progression and its role in early seed development. Here, we compare our conclusions on the regulation of AtTMPK and those of other genes participating in DNA replication, including DPB2, a subunit of the DNA polymerase epsilon complex. Although, the dual localization of AtTMPK in the cytosol and mitochondria seems to be unique to plants, this phenomenon of multiple targeting is also used for other proteins involved in DNA replication, such as DNA ligase 1 (AtLIG1), and may represent a way to coordinate nuclear and organellar divisions.

Open Access Article

Integration of water stress response: Cell expansion and cuticle deposition in Arabidopsis thaliana

Eleonora Cominelli, Massimo Galbiati and Chiara Tonelli
Pages 556 - 557
http://dx.doi.org/10.4161/psb.3.8.5699
Abstract | PDF

Inhibition of cell expansion and modification in the accumulation of cuticle components are two important processes that plants adopted to respond to water deficit. In our recent publication in Plant Journal we characterized an Arabidopsis thaliana transcription factor, belonging to the R2R3-MYB family, specifically expressed in response to water deficit, involved in the regulation of these two processes. The over-expression of this gene causes both the reduction of mRNA level of some genes involved in cell expansion and the accumulation of transcript of genes with a putative role in cuticle synthesis and deposition. In this addendum we propose a model for the function of this transcription factor as an integrator of the pathway that induces cuticle components synthesis and deposition and the process that blocks cell expansion in response to water stress.

Open Access Article

Integration of stress produced reactive oxygen species in the stomatal regulation of micropropagated Vitis vinifera L. plantlets impaired in ABA signalling

B. Jorge Vilela, Luísa C. Carvalho and Sara Amâncio
Pages 558 - 559
http://dx.doi.org/10.4161/psb.3.8.5700
Abstract | PDF

Reactive oxygen species (ROS) have been repeatedly implicated as cellular second messengers important in the modulation of almost every ontogenic phase of plant development, from seedling to cell death. In all of these processes, ROS production and detoxification are highly regulated and its levels are kept under tight control, in order to achieve the desired effect at the cellular or plant level. Micropropagated Vitis vinifera L. transferred to ex vitro growth under increased irradiance gave an additional insight into ROS signalling by integrating stress produced hydrogen peroxide (H₂O₂) into normal signalling pathways with distinctive effects critical for the survival, growth and development of these plants. Here we discuss in further detail the relevance of these results and propose a model that may explain this phenomenon.

Open Access Article

The molecular language of semagenesis

Andrew G. Palmer, Yue Liu, Samantha M. Adkins, Xiao Zhang, I-Lin Wu, Xianyu Chen and David G. Lynn
Pages 560 - 561
http://dx.doi.org/10.4161/psb.3.8.5703
Abstract | PDF

Semagenesis, the process of signal generation, is a novel signaling strategy first uncovered within the parasitic plants. Recent evidence suggests that the parasite's production of reactive oxygen species (ROS) has been focused externally to exploit the host's innate immunity. Here we use the inducer identified from decoding semagenesis, as well as other signaling strategies of the parasitic plants, to synchronize host commitments of Striga asiatica and reveal the molecular events that control plant development.

Open Access Article

CPR5, a Jack of all trades in plants

Hai-Chun Jing and Paul P. Dijkwel
Pages 562 - 563
http://dx.doi.org/10.4161/psb.3.8.5708
Abstract | PDF

In our recent paper in Journal of Experimental Botany, we examined the effects of cpr5/old1 mutations and CPR5 overexpression on Arabidopsis growth and development. We found that CPR5 is important for early plant growth but promotes senescence at late development and hence proposed it as a senescence-regulatory gene as predicted by the Evolutionary Theory of Senescence derived from studies on animal ageing. One of the key unsolved issues is how CPR5 contributes to the early plant growth and development. Here we discuss the possible cellular functions of CPR5.

Open Access Article

Arabidopsis bax inhibitor-1: A rheostat for ER stress-induced programmed cell death

Naohide Watanabe and Eric Lam
Pages 564 - 566
http://dx.doi.org/10.4161/psb.3.8.5709
Abstract | PDF

Unfolded and misfolded proteins in the endoplasmic reticulum (ER) of eukaryotic cells elicit a highly conserved unfolded protein response (UPR) that leads to an increase in the capacity of the ER to deal with protein folding by hightened expression of enzymes such as chaperone and protein disulfide isomerases. However, cells die by apoptosis if the function of the ER cannot be restored in metazoans. To what extent is this mechanism evolutionarily conserved in plant cells remains to be elucidated. Emerging data from our recent study now provide compelling evidence that a conserved cell death suppressor, BAX inhibitor-1 (BI-1), plays a pivotal role as a survival factor against endoplasmic reticulum stress-mediated programmed cell death (PCD) that likely acts in parallel to the UPR pathway. This finding suggests a clear functional correlation to the predicted ER localization of AtBI1 as well as directly implicating the ER of plant cells as an important modulator of cell death activation. Furthermore, ER stress and its associated cell death in plants can be relieved by administration of chemical chaperones which have been clinically used for treatment of many human diseases linked to neurodegenerative disorders that are triggered by the dysfunction of ER homeostasis. This opens the way for future studies to decipher the mechanisms and pathways of ER-mediated PCD, and function of this pathway in plant development and stress response.

Open Access Article

Lessons from investigation of regulation of APS reductase by salt stress

Anna Koprivova and Stanislav Kopriva
Pages 567 - 569
http://dx.doi.org/10.4161/psb.3.8.5716
Abstract | PDF

Exposure to high salinity affects plant ion homeostasis, water relations, and results in oxidative stress. Therefore, various processes are induced as salt stress response including antioxidative defense systems. The tripeptide glutathione has a prominent position among the metabolites involved in such stress defense. Glutathione synthesis is dependent on supply of cysteine and thus on the assimilation of sulfate. We have investigated how the key enzyme of sulfate assimilation, adenosine 5'phosphosulfate (APS) reductase is regulated by salt stress in Arabidopsis roots. Using Arabidopsis mutants in various signaling pathways we aimed to identify the signaling cascade leading to regulation of APS reductase by NaCl. We found the enzyme to be regulated by a complex signaling network on transcriptional and post-transcriptional levels with responses of mRNA accumulation and enzyme activity largely uncoupled. Here we want to share the important lessons we have learned from this investigations.

Open Access Article

Feedback control of reactive oxygen and Ca²⁺ signalling during brown algal embryogenesis

Susana M.B. Coelho, Colin Brownlee and John H.F. Bothwell
Pages 570 - 572
http://dx.doi.org/10.4161/psb.3.8.5730
Abstract | PDF

In a recent paper in Planta, we combined novel confocal reflectance imaging of intracellular reactive oxygen species (ROS) with inhibition-of-growth experiments to show that ROS help to direct polarized growth in brown algal zygotes. Using confocal fluorescence imaging of intracellular Ca²⁺ distributions, we were also able to show an interaction between ROS and Ca²⁺ signalling. The modulation of intracellular Ca²⁺ signals by reactive oxygen species (ROS) is a common motif in many plant and algal systems, but our Planta paper is its first demonstration during early development. We explain here how our findings complement a number of recent studies on polarized growth in plant and algal systems.

Open Access Article

Subcellular localization of flavonoid natural products: A signaling function?

Marina Naoumkina and Richard A. Dixon
Pages 573 - 575
http://dx.doi.org/10.4161/psb.3.8.5731
Abstract | PDF

In a recent paper in Proceedings of the National Academy of Sciences USA, we described genetic mechanisms for the mobilization of pre-formed vacuolar glycoconjugates of isoflavone intermediates for phytoalexin biosynthesis in response to the wound signal methyl jasmonate. While addressing the cellular localizations of glycosyl hydrolases (GHs) that could function in this mobilization, we observed that one jasmonate-induced GH localized to the nucleus, along with a potential product of its activity (7,4’-dihydroxyflavone). These and other observations on the nuclear localization of flavonoids suggest the possibility of as yet unidentified signaling functions for natural products to regulate pathways necessary for plant defense.

Open Access Article

Subcellular localization of overexpressed maize AChE gene in rice plant

Kosuke Yamamoto and Yoshie S. Momonoki
Pages 576 - 577
http://dx.doi.org/10.4161/psb.3.8.5732
Abstract | PDF

The ACh-mediated system consisting of acetylcholine (ACh), acetylcholine receptor (AChR) and acetylcholinesterase (AChE) is fundamental for nervous system function in animals and insects. Although plants lack a nervous system, both ACh and ACh-hydrolyzing activity have been widely recognized in the plant kingdom. The function of the plant ACh-mediated system is still unclear, despite more than 30 years of research. To understand ACh-mediated systems in plants, we previously purified maize AChE and cloned the corresponding gene from maize seedlings (Plant Physiology). In a recent paper in Planta, we also purified and cloned AChE from the legume plant siratro (Macroptilium atropurpureum). In comparison with electric eel AChE, both plant AChEs showed enzymatic properties of both animal AChE and animal butyrylcholinesterase. On the other hand, based on Pfam protein family analysis, both plant AChEs contain a consensus sequence of the lipase GDSL family, while the animal AChEs possess a distinct alpha/beta-hydrolase fold superfamily sequence, but no lipase GDSL sequence. Thus, neither plant AChE belongs to the well-known AChE family, which is distributed throughout the animal kingdom. To address the possible physiological roles of plant AChEs, we herein report our data from the immunological analysis of the overexpressed maize AChE gene in plants.

Open Access Article

Cyclins D, phytoregulators and cell cycle onset in germinating maize

Jorge M. Vázquez-Ramos and Aurora Lara-Núñez
Pages 578 - 579
http://dx.doi.org/10.4161/psb.3.8.5733
Abstract | PDF

Several different D-type cyclins can be found in plants and in maize, four of these have been characterized: CycD2;1, CycD4;1, CycD5;1 and CycD5;2. These cyclins appear to form complexes with Cdks, with PCNA and also with KRP proteins and in these kinase activity can be measured. The expression of the corresponding genes during maize germination is highly stimulated by phytohormones like auxin and cytokinin, however this is not followed by an equivalent increase in the amount of the corresponding proteins; nonetheless, auxins do stimulate the associated kinase activity, particularly at early germination times. Thus, auxins appear to stimulate the cell cycle during germination at two levels, transcription and kinase activation. Both auxins and cytokinins appear to shorten the G1 phase during germination and stimulate DNA synthesis, but apparently they do it in different ways as the simultaneous addition of both to germinating maize axes eliminates DNA synthesis stimulation. Therefore, similar actions may be achieved by different paths.

Open Access Article

Host foraging for differentially adapted Brassica-feeding aphids by the Braconid parasitoid Diaeretiella rapae

James D. Blande, John A. Pickett and Guy M. Poppy
Pages 580 - 582
http://dx.doi.org/10.4161/psb.3.8.5734
Abstract | PDF

Interactions occurring in a tritrophic system comprising plants, aphids and parasitoids are of great complexity. The generalist endoparasitoid Diaeretiella rapae McIntosh (Hymenoptera: Aphidiidae) displays specialist characteristics on brassica feeding aphids. Previously, we studied differential signalling to D. rapae by specialist and generalist brassica feeding aphids on turnip. We reported no differences in the attractiveness of volatile compounds from the two turnip/aphid complexes. However, we reported a significantly greater D. rapae attack rate on the specialist Lipaphis erysimi (Kaltenbach) than the generalist Myzus persicae (Sulzer). As a consequence we predicted that D. rapae would forage more efficiently and produce more offspring on L. erysimi. We present here some additional data collected in a more complex spatial/temporal environment in large experimental chambers and discuss this drawing attention to the need for careful interpretation of mechanistic information in predicting the overall foraging process.

Open Access Article

Blocking and triggering of plant immunity by Pseudomonas syringae effector AvrPto

Na Zong, Tingting Xiang, Yan Zou, Jijie Chai and Jian-Min Zhou
Pages 583 - 585
http://dx.doi.org/10.4161/psb.3.8.5741
Abstract | PDF

Bacterial effectors are double-edged swords that enhance bacterial virulence in susceptible plants while trigger resistance in plants carrying cognate resistance proteins. A well-known example of this is Pseudomonas syringae protein AvrPto that is delivered into plant cells through the type III secretion system. AvrPto inhibits immune responses in Arabidopsis plants but triggers resistance in some tomato plants carrying cognate resistance proteins Pto, a serine/threonine kinase, and Prf, a nucleotide-binding leucine-rich repeat protein. In a recent structural study we showed that AvrPto is an inhibitor of the Pto protein kinase. Because Pto closely resemble the kinase domain of receptor kinases, which include pattern recognition receptors (PRRs) crucial for plants to detect invading pathogens, we tested the possibility that PRRs such as FLS2 and EFR are targeted by AvrPto in susceptible plants. Indeed, AvrPto is capable of binding the FLS2 and EFR kinases to block plant immune responses when expressed in protoplasts. In Arabidopsis plants containing FLS2, the P. syringae strain lacking avrPto is compromised in its ability to multiply. However, the defect of the avrPto-deletion strain was alleviated in fls2 plants, indicating a role of AvrPto in overcoming FLS2-mediated resistance. Interestingly, the FLS2-AvrPto and Pto-AvrPto interactions share significant similarity, raising the tantalizing possibility that Pto has evolved as a molecular decoy of the intended targets of AvrPto.

Open Access Article

Phyllotaxis as an example of the symbiosis of mechanical forces and biochemical processes in living tissue

Alan C. Newell, Patrick D. Shipman and Zhiying Sun
Pages 586 - 589
http://dx.doi.org/10.4161/psb.3.8.6223
Abstract | PDF

Phyllotaxis, the arrangement of a plant's phylla (flowers, bracts, stickers) near its shoot apical meristem (SAM), has intrigued natural scientists for centuries. Even today, the reasons for the observed patterns and their special properties, the physical and chemical mechanisms which give rise to strikingly similar configurations in a wide variety of plants, the almost-constant golden divergence angle, the almost constant plastichrone ratio, the choices of parastichy numbers and the prevalence of Fibonacci sequences to which their numbers belong, are at best only partially understood. Our goals in this Addendum are: i) To give a brief overview of current thinking on possible mechanisms for primordia (the bumps on the plant surface which eventually mature into fully developed structures such as leaves or florets) formation and give a descriptive narrative of the mathematical models which encode various hypotheses. ii) To emphasize the point that patterns, whether they be phyllotactic configurations on plant surfaces or convection cells on the sun's surface, are macroscopic objects whose behaviors are determined more by symmetries of the proposed model and less by microscopic details. Because of this, the identification of observations with the predications of a particular model can only be made with confidence when the match coincides over a range of circumstances and parameters. iii) To discuss some of the key results of the proposed models and, in particular, introduce the prediction of a new and, in principle, measurable invariant in plant phyllotaxis. iv) To introduce a new model of primordia formation which is more in keeping with the pictures and paradigms of Hofmeister,1 Snow & Snow,2 and Douady and Couder3,4 which see primordia as forming in a fairly narrow annular zone surrounding the plant's SAM separating a region of undifferentiated cells from a fully developed patterned state. v) To consider the challenge of phyllotaxis in the broader context of pattern formation in biological tissue which responds to both mechanical and biochemical processes.

Addendum to: Newell AC, Shipman P, Sun Z. Phyllotaxis: Cooperation and competition between biomechnical and biochemical processes. J Theor Biol 2008; 251:421-39.

Open Access Article

The slender phenotype of pea is deficient in DELLA proteins

John J. Ross, James B. Reid, Ian C. Murfet and Diana E. Weston
Pages 590 - 592
http://dx.doi.org/10.4161/psb.3.8.6224
Abstract | PDF

The recent cloning of the pea genes LA and CRY has historical implications, since the combined effect of null mutations in these genes is the elongated, gibberellin-insensitive “slender” phenotype, which gave rise to the theory that gibberellins (GAs) are inhibitors of inhibitors of growth. Interestingly, the duplication event that produced the second gene (LA or CRY) appears to have occurred more than 100 mya, and yet the two genes have retained essentially similar functions. They both encode DELLA proteins, which inhibit growth while at the same time promoting the synthesis of the growth-promoting hormone, gibberellin (GA). This duality of function is discussed in the context of recent suggestions that DELLAs integrate multiple hormone signals, rather than just the GA signal. We also present new data showing that LA and CRY play a major role in regulating fruit growth.

Addendum to: Weston DE, Elliott RC, Lester DR, Rameau C, Reid JB, Murfet IC, Ross JJ. The pea DELLA proteins LA and CRY are important regulators of gibberellin synthesis and root growth. Plant Physiol 2008; 147:199-205.

Open Access Article

Interactions between the circadian clock and cold-response in Arabidopsis

Carmen Espinoza, Zuzanna Bieniawska, Dirk K. Hincha and Matthew A. Hannah
Pages 593 - 594
http://dx.doi.org/10.4161/psb.3.8.6340
Abstract | PDF

Low temperature negatively affects plant growth and metabolism. Plant responses to cold involve massive transcriptional changes, and much effort has been made to identify these changes and their contribution to freezing tolerance. However, the influence of differences in environmental and developmental factors between experiments had not been investigated. We found that diurnal- and circadian-regulated genes are responsible for the majority of variation between experiments. Moreover, we demonstrated that the cyclic expression pattern of circadian clock components is affected by cold and that the cold induction of many transcription factors is dependent on the time of day. This means that genes identified so far as cold responsive are dependent on the time of day the experiment was performed and that paired diurnal controls are not sufficient to correct for this effect. Ongoing work to dissect the biological relevance of cold-diurnal regulatory interactions demonstrated that some circadian mutants have altered freezing tolerance but that time-of-day appears not to affect freezing tolerance.

Addendum to: Bieniawska Z, Espinoza C, Schlereth A, Sulpice R, Hincha DK, Hannah MA. Disruption of the Arabidopsis circadian clock is responsible for extensive variation in the cold-responsive transcriptome. Plant Physiol 2008; 147:263-79.

Open Access Article

Mechanisms of thermoregulation in plants

Jennifer R. Watling, Nicole M. Grant, Rebecca E. Miller and Sharon A. Robinson
Pages 595 - 597
http://dx.doi.org/10.4161/psb.3.8.6341
Abstract | PDF

Endothermic heating of floral tissues and even thermoregulation is known to occur in a number of plant species across a wide taxonomic range. The mechanisms by which flowers heat, however, are only just beginning to be understood, and even less is known about how heating is regulated in response to changes in ambient temperature. We have recently demonstrated that the alternative pathway of respiration, in which the alternative oxidase (AOX) rather than cytochrome C (COX) acts as terminal electron acceptor, is responsible for heat generation in one thermoregulating species, the sacred lotus (Nelumbo nucifera). In the March issue of the Journal of Experimental Botany we further demonstrated that AOX-mediated heat production in this species is regulated at both the level of gene expression and also post-translationally. Similarly, AOX has also been implicated in heat production in other thermogenic species. In this addendum we discuss the central role of AOX in heat production and how post-translational mechanisms may provide the fine control necessary for thermoregulation.

Addendum to: Grant NM, Miller RE, Watling JR, Robinson SA. Synchronicity of thermogenic activity, alternative pathway respiratory flux, AOX protein content, and carbohydrates in receptacle tissues of sacred lotus during floral development. J Exp Bot 2008; 59:705-14.

Open Access Article

Metabolome-ionome-biomass interactions: What can we learn about salt stress by multiparallel phenotyping?

Diego H. Sanchez, Henning Redestig, Ute Krämer, Michael K. Udvardi and Joachim Kopka
Pages 598 - 600
http://dx.doi.org/10.4161/psb.3.8.6347
Abstract | PDF

Long-term exposure of plants to saline soil results in mineral ion imbalance, altered metabolism, and reduced growth. Currently, the interaction between ion content and plant metabolism under salt-stress is poorly understood. Here we present a multivariate correlation study on the metabolome, ionome, and biomass changes of Lotus japonicus challenged by salt stress. Using latent variable models, we show that increasing salinity leads to reproducible changes of metabolite, ion and nutrient pools. Strong correlations between the metabolome and the ionome or biomass may allow one to estimate the degree of salt stress experienced by a plant based on metabolite profiles. Despite the apparently high predictive power of the models, it remains to be investigated whether such metabolite profiles of non- or moderately-stressed plants can be used by breeding programs as ideal ideotypes for the selection of enhanced salt-tolerant genotypes.

Addendum to: Sanchez DH, Lippold F, Redestig H, Hannah M, Erban A, Krämer U, Kopka J, Udvardi MK. Integrative functional genomics of salt acclimatization in the model legume Lotus japonicus. Plant J 2008, doi:10.1111/j.1365-313X.2007.03381.x

Open Access Article

Integration of seasonal flowering time responses in temperate cereals

Megan N. Hemming, W. James Peacock, Elizabeth S. Dennis and Ben Trevaskis
Pages 601 - 602
http://dx.doi.org/10.4161/psb.3.8.6352
Abstract | PDF

Our paper describes how the genetic pathways which regulate vernalization and long-day flowering responses are integrated to promote spring flowering in cereals. This process is mediated by the VERNALIZATION1 (VRN1) and VRN2 genes. VRN2 encodes a CONSTANS-like protein that represses FLOWERING LOCUS T (FT1) to block the long-day flowering response until plants are vernalized. When plants are vernalized VRN1, a FRUITFUL-like MADS box transcription factor, is induced. This down-regulates VRN2, allowing long-day induction of FT1 to occur post-vernalization. A comparison of the pathways regulating seasonal induction of flowering in cereals with those of Arabidopsis shows the vernalization response pathway has evolved convergently to regulate the activity of a conserved daylength response pathway in these divergent plant lineages.

Addendum to: Hemming M.N, Peacock W.J, Dennis E.S, Trevaskis B. Low temperature and daylength cues are integrated to regulate FLOWERING LOCUS T in barley. Plant Physiol 2008; 147:355-66.

Open Access Article

Root mucilage enhances aluminum accumulation in Melastoma malabathricum, an aluminum accumulator

Toshihiro Watanabe, Seiji Misawa, Syuntaro Hiradate and Mitsuru Osaki
Pages 603 - 605
http://dx.doi.org/10.4161/psb.3.8.6356
Abstract | PDF

Root mucilage is gelatinous polysaccharide-containing material exuded from the outer layers of the root cap. Although mucilage has been suggested to play several roles in plant growth, its role in mineral uptake has not been well understood. Melastoma malabathricum L. is an aluminum (Al) accumulator growing in tropical acid soils. This species accumulates more than 10 mg Al g-1 DW in leaves and roots. Root mucilage is generally known to immobilize metal cations such as Al in the rhizosphere. However, we found that roots of M. malabathricum exuded large amounts of mucilage. Using the Zea mays L. mucilage as a control, we have recently shown that mucilage of M. malabathricum has unique physical and chemical characteristics, and facilitates Al uptake in this species. Since M. malabathricum cannot grow well in Al-deficient soil (nonacid soils), this species might have developed a mechanism for Al acquisition. We have also discussed the reason for this species' requirement of Al, a nonessential element.

Addendum to: Watanabe T, Misawa S, Hiradate S, Osaki M. Characterization of root mucilage from Melastoma malabathricum, with emphasis on its roles in aluminum accumulation. New Phytol 2008;178:581-9.

Open Access Article

Finding a missing link in MAP kinase cascade

Kwi-Mi Chung and Hiroshi Sano
Pages 606 - 608
http://dx.doi.org/10.4161/psb.3.8.6358
Abstract | PDF

Mitogen-activated protein kinase (MAPK) cascade is one of the major signaling systems in eukaryotes. External signals are tranduced through three protein kinases, which successively relay phosphorylation to finally activate target genes/proteins. However, few information on targets of MAPK have so far been available. In this study, we identified a novel transcription factor, NtWIF, which is directly phosphorylated by a wound-induced protein kinase (WIPK), a typical MAPK from tobacco plants. Phosphorylated NtWIF recognizes the auxin responsive element (ARE), and transcriptionally activates ARE-driven Luciferase-reporter genes. Transgenic tobacco plants, in which NtWIF was overexpressed or suppressed, showed distinct features not only in pathogen resistance, but also in seed development and root growth. Micro-array assay using transgenic lines identified 178 differentially expressed genes, among which nearly half was related to defense and development. Screening of the available promoter regions revealed that multiple genes encoding such as pathogenesis-related protein Q (PR-Q), β-1,3-glucanase, aminocyclopropane carboxylic acid synthase 2, P-450 and WIPK itself possess the ARE motif. Upon coexpression in cultured cells, NtWIF transcriptionally activated the Luciferase-reporter gene driven by intact promoters of PR-Q and WIPK. Since ARE is commonly found in auxin-responsive genes, NtWIF possibly targets diverse genes for defense and development by sharing processes that involve auxins. Transcriptional activation of WIPK by NtWIF suggests that WIPK is produced through a feed-back controlling system. It was thus concluded that NtWIF is a missing link between WIPK and its down-stream proteins, and that WIPK cascade is auto-regulated through a self-amplifying circuit.

Addendum to: Chung K-M, Sano H. Transactivation of wound-responsive genes containing the core sequence of the auxin-responsive element by a wound-induced protein kinase-activated transcription factor in tobacco plants. Plant Mol Biol 2007; 65:763-73.

Open Access Article

Plant polyphenols in cell-cell interaction and communication

Yury S. Tarahovsky
Pages 609 - 611
http://dx.doi.org/10.4161/psb.3.8.6359
Abstract | PDF

Plant polyphenols including flavonoids and tannins are important constituent of our everyday diet and medical herbals. It is broadly accepted that polyphenols may protect us from toxins, carcinogens and pollutants though the mechanisms of the polyphenols action is still not clear. Here we discuss the ability of polyphenols and especially gallate rich compounds like tannins and catechin gallates to interact with proteins and lipids, establish binding between adjacent bilayer surfaces and initiate membrane aggregation. This phenomena discovered in model experiments could also influence lateral segregation and compartmentalization of cell surface compounds and assist the cell-cell interaction and signal transduction. The involvement of plant polyphenols in communication between cells could be an important factor responsible for anticarcinogenic, vascular and cardioprotective activity of these compounds and speculated to be implicated in the evolution of human brain and intelligence.

Addendum to: Tarahovsky YS, Muzafarov EN, Kim YA. Rafts making and rafts braking: how plant flavonoids may control membrane heterogeneity. Mol Cell Biochem 2008; In press.




LETTER TO THE EDITOR

Open Access Article

Bioethics: On the road to absurd land

Simcha Lev-Yadun
Page 612
http://dx.doi.org/10.4161/psb.3.8.6342
PDF