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Volume 6 Special Issue 1 2012
Stress-Mediated Signaling in Plants I
ISBN 978-4-907060-07-7
How to reference: Khatri N, Katiyar A, Mudgil Y (2012) Role of G Protein Signaling Components in Plant Stress Management . In: Girdhar K. Pandey (Ed) Stress-Mediated Signaling in Plants I . Plant Stress 6 (Special Issue 1), 1-9
Guest Editor
Girdhar K. Pandey
CONTENTS AND ABSTRACTS
Nisha Khatri, Arpana Katiyar, Yashwanti Mudgil (India) Role of G Protein Signaling Components in Plant Stress Management (pp 1-9)
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ABSTRACT
Invited Review: Plant growth and development is controlled by several environmental cues, including biotic and abiotic stresses. These changes are sensed through different cell surface receptors, which undergo conformational changes and transmit the signal downstream. These signals are transmitted via intracellular signaling molecules that ultimately modulate gene expression, which in turn helps them to survive the environmental challenge. One such class of receptors is plasma membrane localized G-protein-coupled receptors (GPCR). G proteins have been shown to transduce signals from GPCR. Plant G proteins play important role in both biotic and abiotic stresses. With the availability of G protein core complex component null mutants, it has been shown that G proteins play role in jasmonic acid (JA)-mediated response during infection by Alternaria brassicola and Fusarium oxysporum. While Gα null mutants are less susceptible to necrotrophic pathogen, G protein components have also been found to play a regulatory role in ethylene-mediated hypoxia signaling. Abiotic stress-generated signals also activate G-protein signaling cascade, Gα over expressing plants for instance, showed tolerance to high salinity and high temperature whereas over expression of Gβ showed tolerance to high temperature. RGS1 (Regulator of G-protein Signaling1) over-expression confers drought tolerance via ABA mediated pathway by stimulating the expression of enzymes involved in biosynthesis of ABA. In plants, very few effectors of G protein signaling were known, until recently with the availability of G protein signaling interactome in Arabidopsis, proteins have been re-discovered as novel component of G protein signaling pathway. Some of these are plant homologs of animal proteins with known/predicted function in stress, but their role in plants is yet to be discovered. In this review, we focus on the involvement of G-protein signaling components during biotic and abiotic stress.
Amarjeet Singh, Amita Pandey, Girdhar K. Pandey (India) Phospholipase D in Stress Activated Lipid Signaling in Plants (pp 10-17)
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ABSTRACT
Invited Review: Phospholipid hydrolysing enzymes, phospholipase D are represented by multiple gene members encoding various isoforms in plants. Different PLD isoforms display a varying requirement for the Ca2+ and the substrate lipid molecules for their function. By hydrolysing the phosphodiester bond of phospholipids and generating phosphatidic acid (PA), and a soluble head group, phospholipase D regulates various cellular processes in plants such as abscisic acid (ABA) signaling, programmed cell death, defense response to wounding and pathogens, root growth, freezing tolerance and other physiological responses. Studies suggest association of phospholipase D members with various biotic and abiotic stresses and their possible role in stress mediated signaling in plants, as their transcript level and protein activity changes upon exposure to stress stimuli. The focus of this review is discussion of the expression pattern and the functional role of different phospholipase D isoforms under various abiotic and biotic stresses, and the modulation of the stress signaling events leading to stress adaptation and tolerance in plants.
Hyunmi Kim, Kyeyoon Lee, Hyunsik Hwang, In Sun Yoon, Dool-Yi Kim, Taekryun Kwon, Myung-Ok Byun, Beom-Gi Kim (Korea) The Orthologues of ABA Receptors and ABA Signaling Components in Rice (pp 18-28)
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ABSTRACT
Invited Review: Abscisic acid (ABA) is a multi-functional plant hormone that acts in several different physiological processes such as stomata closing, seed dormancy, abiotic stress adaptation and developmental differentiation. Many efforts have been made over the last decades to identify the molecular mechanisms of ABA signal transduction pathways. In particular, the identification of the ABA receptors has been one of the most important issues facing this research area. Recently, ABA receptors, including two GPCR-type G proteins, a Mg-chelatase H subunit and PYL/RCARs were reported to bind ABA and to be involved in ABA-dependent responses in seed dormancy, stomata closure and abiotic stress adaptation in Arabidopsis thaliana. In particular cytosolic ABA receptor PYL/RCARs are considered the major regulators of ABA dependent gene expression. The signaling components consisted of PYR/RCAR, subclass A PP2C, SnRK2 and ABF studied well and the crystal structures of the components and complexes were identified in Arabidopsis. In this review, we describe ABA receptors and signaling components of Arabidopsis and identify the rice orthologues corresponding to ABA receptors and signaling components of Arabidopsis by homology searches in the rice database. This also suggested that the receptors and signaling components of ABA are highly conserved in dicot and monocot plants evolutionarily.
Ashish Kumar Srivastava, Penna Suprasanna, Stanislaus Francis D’Souza (India) Interaction and Crosstalk Between Calcium and Redox Signaling Events in Plants (pp 29-36)
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ABSTRACT
Invited Review: In response to any stimulus, various cellular responses are triggered among, which the most rapid responses include the induction of calcium and reactive oxygen species (ROS) transients. The induction of calcium transient is due to the concerted action of calcium dependent channels, pumps, and carriers situated in the plasma membrane and different sub-cellular compartments. The spatial and temporal nature of the calcium transient is defined as cellular “Ca2+ signature” and is responsible for the activation of stimulus-specific calcium sensor and decoder elements. The redox state of the cell under any condition is defined as the integrative ratio of reduced to oxidized form of redox couples present inside the cell. The induction of calcium transient is coherent with the significantly higher level of ROS, which shifts the redox status of the cell to a more oxidized state. This change occurs in a dose dependent manner and is sensed in calcium signaling dependent manner. The complex and coordinated interaction of calcium and redox events is responsible for the generation of stimulus-specific response. The present article deals with the overview of calcium and redox signaling events and their possible crosstalk to regulate different plant functions under normal and stressful environment.
Arsheed Hussain Sheikh, Hussain Ara, Alok Krishna Sinha (India) Mitogen Activated Protein Kinases: A Hunt for their Physiological Substrates in Plants (pp 37-42)
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ABSTRACT
Invited Mini-Review: Mitogen activated protein kinases (MAPKs) are important signal transducing enzymes that connect various sensors/receptors to a wide range of cellular responses in mammals, yeast and plants. The MAPKs are part of a phospho-relay cascade, which essentially consists of three components namely MAPK kinase kinase (MAPKKK), MAPK kinase (MAPKK) and MAPK. They are connected to each other by an event of phosphorylation. MAPK, the last component of the cascade, upon activation phosphorylates variety of cytosolic and nucleic proteins for appropriate cellular reorganization. In plants MAPK consist of a multigene family having twenty and sixteen members in Arabidopsis and rice, respectively. Though search for the substrate of MAPK in plants is on, there are only a few reports of phosphorylation of downstream targets by activated MAPK. In the present review we take an overview of the progress made in identifying the substrate of MAPK in plants, the approaches undertaken and finally discuss the future perspectives in hunt for the putative substrates.
Swatismita Ray (India) Calcium-Dependent Protein Kinase: A Tool for Plants to Crack the Calcium Code (pp 43-59)
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ABSTRACT
Invited Review: Ca2+ signals are involved in most aspects of growth and development of plant, including response to hormone signaling, various biotic and abiotic stresses, germination, cell division, cell expansion, pollen tube growth and fertilization. The calcium-dependent protein kinases (CDPKs) constitute one of the largest Ca2+ sensing subfamilies of plant-specific protein kinases that decodes the transient changes of Ca2+ concentration in the cytoplasm in response to extrinsic and intrinsic cues. The unique domain structure of CDPKs makes them not only “sensors” but also “responders” to these Ca2+ signatures. A multigene family consisting of 34, 31 and 20 genes in Arabidopsis, rice and wheat, respectively, encodes CDPKs. The multigenic nature and diverse spatial and temporal differential expression have been reported in many plant species, which emphasizes on the precise role of isoforms in developmental (e.g. pollen tube) as well as stress responsive pathways (e.g. ROS). The regulation of CDPKs has been reported to be at transcriptional and post translational level. The signaling pathways mediated by CDPKs have also been found to overlap with MAP kinase pathways, suggesting of an intricate network, which regulate precise responses of plants. The proteins interacting with CDPKs are diverse in their function (e.g. transcription factor, channel protein, v-SNARE) which indicates that CDPKs play important role in regulating the Ca2+ signaling cascade, leading to extremely precise response of plants during development and adaptation to environmental cues. This functional diversity and their cross-talks are being discussed in this review.
Akhilesh K. Yadav, Amita Pandey, Girdhar K. Pandey (India) Calcium Homeostasis: Role of CAXs Transporters in Plant Signaling (pp 60-69)
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ABSTRACT
Invited Review: Calcium is an essential macronutrient as well as an ubiquitous second messenger, playing a pivotal role in plant growth and development. The neutral cytosolic pH, acidic apoplastic and vacuolar pH is maintained by synergistic action of different channels/transporters in plant cells. In the cytosol, a submicro-molar range of calcium is maintained for efficient biochemical and physiological functioning including calcium-mediated signal transduction. A concerted interplay of channels/transporters, mediating influx and efflux of ions across membranes, tightly regulates the concentration of calcium in the cytosol by sequestering extra calcium into vacuole. For calcium homeostasis, the pre-requisite is to balance and maintain high calcium level in cytoplasm during signaling events and subsequently counterbalanced after the removal of the signal. Hence, the major mechanism in plant cell for calcium homeostasis is redistribution of calcium and other cation in exchange for the H+ generated by various H+ pumps and antiporters. Calcium/cation antiporter (CaCA) superfamily consist of five families, one of them is CAX multigene family (H+/cation exchangers). In last two decades, several studies have been reported involving discovery of biochemical, physiological and molecular characterization of CAX family members extensively. CAX proteins are mainly constituted in vacuolar membrane and responsible for maintaining low cytosolic Ca2+ and/or other cations against their concentration gradient in cells. CAX family play an important role in calcium signaling, ion compartmentalization, sequestering of essential and heavy metal ions in vacuole. CAXs could be agriculturally important to increase the calcium content in edible part of plant and sequester heavy metals from polluted soil. In this review, we are primarily elaborating the functional aspect of CAX protein family in calcium homeostasis and stress mediated signaling in plants.
Marcelo de Oliveira Santos, José Marcello Salabert de Campos, Francisco José Lima Aragão (Brazil) Regulation of Genetic Responses to Salt Stress (pp 70-76)
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ABSTRACT
Invited Mini-Review: Plant response to salinity-induced stress, like most physiological responses, is specie specific. Despite this specificity, the response is often elicitor dependent, which tends to activate a more general response. While stress in plants may be classified as being biotic or abiotic, both types are known to be influenced by signaling pathway. One of the phenotypically well-characterized specific responses in plants is the production of secondary metabolites. However, the overall signaling pattern and its effects on corresponding genes often lead to their differential expression, which turn it specific. This implies that general and specific responses are activated for each situation. Key mediators amongst the chemical entities with specific physiological effects involved in the signaling pathways include jasmonic acid and acetyl salicylic acid, while the more general mediators include plant growth regulators such as auxins and cytokinins. The molecular mechanism of action of these molecules involves promoter activation that bear specific recognition elements, to which transcription factors can bind to enhance or repress the expression of a given gene. The application of high-throughput techniques has shown that microRNA and chromatin remodeling are involved in exposing such regions under different stress conditions. Here, we discuss the observed differences in salt stress tolerance, and sensitivity to high or low exposure to salt in plants, which correlate with varying degrees of the production of secondary metabolites. It is exposed from the perspective of gene expression under plant growth regulators to physiological response. The role of microRNA and chromatin remodeling as signal elements to control gene expression at DNA binding sites, interacting with transcription factors, which may in turn be affected by microRNAs are also discussed.
Ankita Sehrawat, Renu Deswal (India) Protein Tyrosine Nitration in Abiotic Stress in Plants (pp 77-88)
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ABSTRACT
Invited Review: Research in the last two decades has proven, without a doubt, that nitric oxide (NO) is a cytotoxic as well as a signaling molecule in biological systems. NO is one of the nitrogen oxides present in air and being a free radical it is very reactive. It combines readily with all major macromolecules whether it is lipids, nucleic acids or proteins. Lipid and nucleic acid modification by NO are relatively less extensively investigated more so in plants. Proteins are mostly post-translationaly modified by NO. and its derivatives, which together constitute reactive nitrogen species (RNS). Although recently, good progress has been made regarding ‘NO’ signaling in plants but focus has been more on nitrosylation (a covalent addition of NO to free thiol group in a protein). Another modification, which has received relatively little attention is ‘nitration’, which is the addition of a nitro group (NO2) to an amino acid, preferable tyrosine. Abiotic stress conditions contributes to ‘NO’ production enhancing the nitrosative stress. In animal system ‘tyrosine nitration’ is shown to be a ‘nitrosative stress marker’. Current studies in NO signaling hints at a similar scenario in plants. About 150 tyrosine nitrated proteins are known. A generalized increase in nitration by abiotic stress was observed in many plants including Arabidopsis thaliana and Helianthus annuus. Mechanisms and signaling of nitration are being deciphered. Therefore, ‘tyrosine nitration’ with reference to abiotic stress is reviewed in the present review to describe this very new and relatively unexplored research area in plants.
Vivek Raxwal, Surekha Katiyar-Agarwal, Manu Agarwal (India) Structural and Functional Diversity of Plant Heat Shock Factors (pp 89-96)
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ABSTRACT
Invited Review: Eukaryotic response towards abiotic and biotic stress is mediated by production of molecular chaperons like heat shock proteins (HSPs), which protect cellular proteins from damage. These HSPs are under tight regulation of transcription factors known as Heat Shock Factors (HSFs). They bind to the palindromic repeat motif, Heat Shock Element (HSE), present in promoter of stress responsive genes and modulate their expression. Plants have multi member HSF family as compared to other eukaryotes. HSFs have conserved domains of specialised functions, which have been characterised as DNA binding domain, oligomerization domain, nuclear localisation and export signal and C- terminal activation domain. Based on structural peculiarities, plant HSFs have been grouped in three different classes: Class A, B and C. Although plant HSFs are structurally conserved family of DNA binding proteins, they are functionally diverse. Functional diversity and redundancy within HSF members has evolutionary significance in combating variety of stress conditions, which usually occurs in combinations during plant life cycle. HSFs play significant role not only in stress tolerance but also in various aspects of plant development.
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