Plant Signaling & Behavior

Cao, Yang-Rong; Chen, Shou-Yi; Zhang, Jin-Song

doi: 10.4161/psb.3.10.5934pmid: 19513226

Ethylene has long been regarded as a stress-related hormone, but only recently the link between ethylene signaling pathway and salt stress was primarily established. Ethylene signaling modulates salt response at different levels, including membrane receptors, components in cytoplasm, and nuclear transcription factors in the pathway. However the relevant mechanism is still unclear. In this paper, we described how ethylene signaling pathway regulates salt stress response and discussed the challenges of ethylene and receptor signaling in salt response regulation.

Moeder, Wolfgang; Yoshioka, Keiko

doi: 10.4161/psb.3.10.6545pmid: 19513227

Over the last decade a substantial number of lesion mimic mutants (LMM) have been isolated and a growing number of the genes have been cloned. It is now becoming clear that these mutants are valuable tools to dissect various aspects of programmed cell death (PCD) and pathogen resistance pathways in plants. Together with other forward genetics approaches LMMs shed light on the PCD machinery in plant cells and revealed important roles for sphingolipids, Ca2+ and chloroplast-derived porphyrin-metabolites during cell death development.

Heilmann, Ingo

doi: 10.4161/psb.3.10.6620pmid: 19513228

Phosphoinositides (PIs) control various cellular functions of eukaryotic cells. PIs are derived from phosphatidylinositol (PtdIns) by phosphorylation of the inositol-ring in the lipid-head group; the action of specific lipid kinases gives rise to a family of structurally-related PIs representing PtdIns-mono-, bis-, and -trisphosphates. Specific PIs, such as phosphatidylinositol-4,5-bisphosphate (PtdIns(4,5)P2), can influence more than one physiological process, raising the question as to how interactions with alternative protein partners are coordinated. Previous studies have proposed that PIs are organized by spatiotemporal compartmentation into distinct functional pools, however, mechanisms for the generation and maintenance of such pools has not been presented. Several recent studies now indicate that not only the distinctive inositolpolyphosphate head groups may be relevant for PI function but also the associated fatty acyl-moieties, which may be involved in sorting of lipid precursors into distinct pools. This mini-review aims at highlighting recent evidence that PI acyl-groups exert relevant effects on signaling.

Jia, Wensuo; Zhang, Jianhua

doi: 10.4161/psb.3.10.6294pmid: 19513229

As the nerve-mediated signaling in animals, long-distance signaling in plants is a prerequisite for plants to be able to perceive environmental stimuli and initiate adaptive responses. While intracellular signal transduction has been attracting considerable attentions, studies on long-distance signaling in plants has been relatively overlooked. Stomatal movements are well recognized as a model system for studies on cellular signal transduction. It has been demonstrated that the stomatal movements may be frequently tuned by long-distance signaling under various environmental stimuli. Stomatal movements can not only respond to persistent stress stimuli but also respond to shock stress stimuli. Stomatal responses to drought stress situations may be best characterized in terms of interwoven networks of chemical signaling pathways playing predominant roles in these adaptive processes. In cases of shock stress stimuli, stomatal movements can be more sensitively regulated through the long-distance signaling but with distinctive patterns not observed for drought or other persistent stresses. Here, the fundamental characteristics of stomatal movements and associated long-distance signaling are reviewed and the implications for plant responses to environmental stresses are discussed.

Markin, Vladislav S.; Volkov, Alexander G.; Jovanov, Emil

doi: 10.4161/psb.3.10.6041pmid: 19513230

The Venus flytrap (Dionaea muscipula Ellis) captures insects with one of the most rapid movements in the plant kingdom. We investigated trap closure by mechanical and electrical stimuli using the novel charge-injection method and high-speed recording. We proposed a new hydroelastic curvature mechanism, which is based on the assumption that the lobes possess curvature elasticity and are composed of outer and inner hydraulic layers with different hydrostatic pressure. The open state of the trap contains high elastic energy accumulated due to the hydrostatic pressure difference between the hydraulic layers of the lobe. Stimuli open pores connecting the two layers, water rushes from one hydraulic layer to another, and the trap relaxes to the equilibrium configuration corresponding to the closed state. In this paper we derived equations describing this system based on elasticity Hamiltonian and found closing kinetics. The novel charge-injection stimulation method gives insight into mechanisms of the different steps of signal transduction and response in the plant kingdom.

Guo, Biwei; Irigoyen, Sonia; Fowler, Tiffany B.; Versaw, Wayne K.

doi: 10.4161/psb.3.10.6666pmid: 19513231

Plastids rely on multiple phosphate (Pi) transport activities to support and control a wide range of metabolic processes, including photosynthesis and carbon partitioning. Five of the six members of the PHT4 family of Pi transporters in Arabidopsis thaliana (PHT4;1-PHT4;5) are confirmed or predicted plastid proteins. As a step towards identifying the roles of individual PHT4 Pi transporters in chloroplast and non-photosynthetic plastid Pi dynamics, we used promoter-reporter gene fusions and quantitative RT-PCR studies, respectively, to determine spatial and diurnal gene expression patterns. PHT4;1 and PHT4;4 were both expressed predominantly in photosynthetic tissues, although expression of PHT4;1 was circadian and PHT4;4 was induced by light. PHT4;3 and PHT4;5 were expressed mainly in leaf phloem. PHT4;2 was expressed throughout the root, and exhibited a diurnal pattern with peak transcript levels in the dark. The remaining member of this gene family, PHT4;6, encodes a Golgi-localized protein and was expressed ubiquitously. The overlapping but distinct expression patterns for these genes suggest specialized roles for the encoded transporters in multiple types of differentiated plastids. Phylogenetic analysis revealed conservation of each of the orthologous members of the PHT4 family in Arabidopsis and rice, which is consistent with specialization, and suggests that the individual members of this transporter family diverged prior to the divergence of monocots and dicots.

Coba de la Peña, Teodoro; Cárcamo, Claudia B.; Lucas, M. Mercedes; Pueyo, José J.

doi: 10.4161/psb.3.10.5873pmid: 19704559

Cytokinin receptors (CRs) are hybrid-type histidine kinases, membrane proteins with a cytokinin-binding extracellular domain. CRs initiate and propagate cytokinin signaling by means of phosphorylation and phosphotransfer to downstream proteins. In legumes, some members of the CR multigenic family are essential for nodulation. In two recent works, we investigated the involvement of two new CRs, MsHK1 from Medicago sativa, and LaHK1 from Lupinus albus, in nodule morphogenesis, senescence and stress response. LaHK1 expression increased during the first stages of lupin nodule development, while MsHK1 expression was localized in the meristem and the invasion zone of alfalfa nodules pointing to a role for CRs in nodule cell proliferation and differentiation. Both CRs were also induced during nodule senescence. MsHK1 expression increased under osmotic stress and both genes were induced following dark stress, indicating that CRs are also likely to play a significant role in the response to stress. We propose multiple roles for CRs which, when analyzed jointly with recent results from other authors, suggest coordinated cross-talk of different signaling systems. Addendum to: Coba de la Peña T, Cárcamo CB, Almonacid L, Zaballos A, Lucas MM, Balomenos D, Pueyo JJ. A salt stress-responsive cytokinin receptor homologue isolated from Medicago sativa nodules. Planta 2008; 227:769-79. and Coba de la Peña T, Cárcamo CB, Almonacid L, Zaballos A, Lucas MM, Balomenos D, Pueyo JJ. A cytokinin receptor homologue is induced during root nodule organogenesis and senescence in Lupinus albus L. Plant Physiol Biochem 2008; 46:219-25.

Ramírez, Leonor; Graziano, Magdalena; Lamattina, Lorenzo

doi: 10.4161/psb.3.10.5874pmid: 19704560

Plants respond to iron deprivation by inducing a series of physiological and morphological responses to counteract the nutrient deficiency. These responses include: (i) the acidification of the extracellular medium, (ii) the reduction of ferric ion and (iii) the increased transport of ferrous ion inside of root cells. This iron transport system is present in strategy I plants and is strictly regulated; at low iron concentration the responses are induced whereas upon iron supply they are repressed. The mechanisms related with this process has been extensively studied, however, the specific cellular effectors involved in sensing iron deficiency, the cascade of components participating in signal transduction, and the way iron is metabolized and delivered, are yet poorly understood. Recently, it has been proposed nitric oxide (NO) as a signaling molecule required for plant responses to iron deficiency. NO is produced rapidly in the root epidermis of tomato plants that are growing under iron deficient conditions. Furthermore, it was demonstrated that NO is required for the expression and activity of iron uptake components in roots during iron deprivation. Here we propose and discuss a working hypothesis to understand the way NO is acting in plants responses to iron deficiency. We specifically highlight the cross talk between NO and plant hormones, and the interaction between NO, iron and glutathione for the formation of dinitrosyl iron complexes (DNICs). Finally, a potential role of DNICs in iron mobilization is proposed. Addendum to: Graziano M, Lamattina L. Nitric oxide accumulation is required for molecular and physiological responses to iron deficiency in tomato roots. Plant J 2007; 52:949-60.

Hyun, Youbong; Lee, Ilha

doi: 10.4161/psb.3.10.5875pmid: 19704561

Jasmonic acid (JA) is a lipid-derived plant hormone that mediates diverse biological phenomena. It is one of major goals in JA research field to elucidate the regulatory mechanism of JA level. Recently, we have demonstrated cooperative and differentiated roles of two chloroplast localized galactolipases, DGL (DONGLE) and DAD1 (DEFECTIVE IN ANTHER DEHISCENCE 1), for the regulation of JA content. The DGL maintains a basal level of JA in unwounded vegetative tissues, while the DAD1 is involved in JA production in floral tissues. The JA in vegetative tissues regulates cell expansion while the JA produced in flowers regulates pollen maturation. After wounding, the cooperative function of DGL and DAD1 causes drastic increase of JA. The analysis of induction kinetics showed that the two enzymes have temporally separated roles in wound response; DGL in early phase and DAD1 in late phase of JA production. In this addendum, we discuss the implications of our recent findings and extend our working model for JA homeostasis in plants. Addendum to: Hyun Y, Choi S, Hwang HJ, Yu J, Nam SJ, Ko J, Park JY, Seo YS, Kim EY, Ryu SB, Kim WT, Lee YH, Kang H, Lee I. Cooperation and functional diversification of two closely related galactolipase genes for jasmonate biosynthesis. Dev Cell 2008; 14:183-92.

Hu, Jianping; Desai, Mintu

doi: 10.4161/psb.3.10.5876pmid: 19704562

Peroxisomes are multifunctional organelles whose abundance and metabolic activities differ depending on the species, cell type, developmental stage, and prevailing environmental conditions.1 However, little is known about the signaling pathways that control these variations, especially in plants. Our laboratory recently investigated the regulatory role of light in changes in peroxisome abundance and identified a phytochrome. A-dependent pathway responsible for the proliferation of peroxisomes during dark-to-light transition in Arabidopsis seedlings. Light induces peroxisome proliferation at least in part through up-regulating the PEX11b gene, which encodes a peroxisomal membrane protein that mediates the early stages of peroxisome multiplication. Activation of PEX11b requires the far-red light receptor phyA, as well as the bZIP transcription factor HYH, which binds directly to the promoter of PEX11b. We conclude that during photomorphogenesis, both the import of leaf-peroxisome enzymes from the cytosol and the induction of peroxisome proliferation take place to prepare seedlings for photosynthesis and photorespiration. In addition to light, other plant peroxisome proliferators may also exert their functions by targeting members of the PEX11 gene family for transcriptional activation. Addendum to: Desai M, Hu J. Light induces peroxisome proliferation in Arabidopsis seedlings through the photoreceptor phytochrome A, the transcription factor HY5 HOMOLOG, and the peroxisomal protein PEROXIN11b. Plant Physiol 2008; 146:1117-27.