Ectopic overexpression of Eleusine coracana CAX3 confers tolerance to metal and ion stress in yeast and Arabidopsis

Ionic and metal toxicity in plants is still a global problem for the environment, agricultural productivity and ultimately poses human health threats when these metal ions accumulate in edible organs of plants. Metal and ion transport from cytosol to the vacuole is considered an important component of metal and ion tolerance and a plant's potential utility in phytoremediation. Finger millet (Eleusine coracana) is an orphan crop but has prominent nutritional value in comparison to other cereals. Previous transcriptomic studies suggested that one of the calcium/proton exchanger (EcCAX3) is strongly upregulated during different developmental stages of spikes development in plant. This finding led us to speculate that high calcium accumulation in the grain might be because of CAX3 function. Moreover, phylogenetic analysis shows that EcCAX3 is more closely related to foxtail millet, sorghum and rice CAX3 protein. To decipher the functional role of EcCAX3, we have adopted complementation of yeast triple mutant K677 (Δpmc1Δvcx1Δcnb1), which has defective calcium transport machinery. Furthermore, metal tolerance assay shows that EcCAX3 expression conferred tolerance to different metal stresses in yeast. The gain-of-function study suggests that EcCAX3 overexpressing Arabidopsis plants shows better tolerance to higher concentration of different metal ions as compared to wild type Col-0 plants. EcCAX3-overexpression transgenic lines exhibits abundance of metal transporters and cation exchanger transporter transcripts under metal stress conditions. Furthermore, EcCAX3-overexpression lines have higher accumulation of macro- and micro-elements under different metal stress. Overall, this finding highlights the functional role of EcCAX3 in the regulation of metal and ion homeostasis and this could be potentially utilized to engineer metal fortification and generation of stress tolerant crops in near future.

Review: Structural-functional relationship of WRKY transcription factors: Unfolding the role of WRKY in plants

WRKY as the name suggests, are the transcription factors (TFs) that contain the signature WRKY domains, hence named after it. Since their discovery in 1994, they have been well studied in plants with exploration of approximately 74 WRKY genes in the model plant, Arabidopsis alone. However, the study of these transcription factors (TFs) is not just limited to model plant now. They have been studied widely in crop plants as well, because of their tremendous contribution in stress as well as in growth and development. Here, in this review, we describe the story of WRKY TFs from their identification to their origin, the binding mechanisms, structure and their contribution in regulating plant development and stress physiology. High throughput transcriptomics-based data also opened a doorway to understand the comprehensive and detailed functioning of WRKY TFs in plants. Indeed, the detailed functional role of each and every WRKY member in regulating the gene expression is required to pave the path to develop holistic understanding of their role in stress physiology and developmental processes in plants.

Voltage-dependent anion channel 3 (VDAC3) mediates P. syringae induced ABA-SA signaling crosstalk in Arabidopsis thaliana

Pathogen severely affects plant mitochondrial processes including respiration, however, the roles and mechanism of mitochondrial protein during the immune response remain largely unexplored. The interplay of plant hormone signaling during defense is an outcome of plant pathogen interaction. We recently discovered that the Arabidopsis calcineurin B-like interacting protein kinase 9 (AtCIPK9) interacts with the voltage-dependent anion channel 3 (AtVDAC3) and inhibits MV-induced oxidative damage. Here we report the characterization of AtVDAC3 in an antagonistic interaction pathway between abscisic acid (ABA) and salicylic acid (SA) signaling in Pseudomonas syringae -Arabidopsis interaction. In this study, we observed that mutants of AtVDAC3 were highly susceptible to Pseudomonas syringae infection as compared to the wild type (WT) Arabidopsis plants. Transcripts of VDAC3 and CIPK9 were inducible upon ABA application. Following pathogen exposure, expression analyses of ABA and SA biosynthesis genes indicated that the function of VDAC3 is required for isochorisimate synthase 1 (ICS1) expression but not for Nine-cis-epoxycaotenoid dioxygenase 3 (NCED3) expression. Despite the fact that vdac3 mutants had increased NCED3 expression in response to pathogen challenge, transcripts of ABA sensitive genes such as AtRD22 and AtRAB18 were downregulated even after exogenous ABA application. VDAC3 is required for ABA responsive genes expression upon exogenous ABA application. We also found that Pseudomonas syringae-induced SA signaling is downregulated in vdac3 mutants since overexpression of VDAC3 resulted in hyperaccumulation of Pathogenesis related gene1 (PR1) transcript. Interestingly, ABA application prior to P. syringae inoculation resulted in the upregulation of ABA responsive genes like Responsive to ABA18 (RAB18) and Responsive to dehydration 22 (RD22). Intriguingly, in the absence of AtVDAC3, Pst challenge can dramatically increase ABA-induced RD22 and RAB18 expression. Altogether our results reveal a novel Pathogen-SA-ABA interaction pathway in plants. Our findings show that ABA plays a significant role in modifying plant-pathogen interactions, owing to cross-talk with the biotic stress signaling pathways of ABA and SA.

Calcium imaging: a technique to monitor calcium dynamics in biological systems

Calcium ion (Ca2+) is a multifaceted signaling molecule that acts as an important second messenger. During the course of evolution, plants and animals have developed Ca2+ signaling in order to respond against diverse stimuli, to regulate a large number of physiological and developmental pathways. Our understanding of Ca2+ signaling and its components in physiological phenomena ranging from lower to higher organisms, and from single cell to multiple tissues has grown exponentially. The generation of Ca2+ transients or signatures for various stress factor is a well-known mechanism adopted in plant and animal systems. However, the decoding of such remarkable signatures is an uphill task and is always an interesting goal for the scientific community. In the past few decades, studies on the concentration and dynamics of intracellular Ca2+ are significantly increasing and have become a trend in modern biology. The advancement in approaches from Ca2+ binding dyes to in vivo Ca2+ imaging through the use of Ca2+ biosensors to achieve spatio-temporal resolution in micro and milliseconds range, provide us phenomenal opportunities to study live cell Ca2+ imaging or dynamics. Here, we describe the usage, improvement and advancement of Ca2+ based dyes, genetically encoded probes and sensors to achieve extraordinary Ca2+ imaging in plants and animals.

Graphical abstract

Characterization of Chlamydomonas voltage-gated calcium channel and its interaction with photoreceptor support VGCC modulated photobehavioral response in the green alga

Calcium (Ca2+) signaling plays a major role in regulating multiple processes in living cells. The photoreceptor potential in Chlamydomonas triggers the generation of all or no flagellar Ca2+ currents that cause membrane depolarization across the eyespot and flagella. Modulation in membrane potential causes changes in the flagellar waveform, and hence, alters the beating patterns of Chlamydomonas flagella. The rhodopsin-mediated eyespot membrane potential is generated by the photoreceptor Ca2+ current or P-current however, the flagellar Ca2+ currents are mediated by unidentified voltage-gated calcium (VGCC or CaV) and potassium channels (VGKC). The voltage-gated ion channel that associates with ChRs to generate Ca2+ influx across the flagella and its cellular distribution has not yet been identified. Here, we identified putative VGCCs from algae and predicted their novel properties through insilico analysis. We further present experimental evidence on Chlamydomonas reinhardtii VGCCs to predict their novel physiological roles. Our experimental evidences showed that CrVGCC4 localizes to the eyespot and flagella of Chlamydomonas and associates with channelrhodopsins (ChRs). Further in silico interactome analysis of CrVGCCs suggested that they putatively interact with photoreceptor proteins, calcium signaling, and intraflagellar transport components. Expression analysis indicated that these VGCCs and their putative interactors can be perturbed by light stimuli. Collectively, our data suggest that VGCCs in general, and VGCC4 in particular, might be involved in the regulation of the photobehavioral response of Chlamydomonas.

Calcium signalling components underlying NPK homeostasis: potential avenues for exploration

Plants require the major macronutrients, nitrogen (N), phosphorus (P) and potassium (K) for normal growth and development. Their deficiency in soil directly affects vital cellular processes, particularly root growth and architecture. Their perception, uptake and assimilation are regulated by complex signalling pathways. To overcome nutrient deficiencies, plants have developed certain response mechanisms that determine developmental and physiological adaptations. The signal transduction pathways underlying these responses involve a complex interplay of components such as nutrient transporters, transcription factors and others. In addition to their involvement in cross-talk with intracellular calcium signalling pathways, these components are also engaged in NPK sensing and homeostasis. The NPK sensing and homeostatic mechanisms hold the key to identify and understand the crucial players in nutrient regulatory networks in plants under both abiotic and biotic stresses. In this review, we discuss calcium signalling components/pathways underlying plant responses to NPK sensing, with a focus on the sensors, transporters and transcription factors involved in their respective signalling and homeostasis.

Deciphering the role of cytoplasmic domain of Channelrhodopsin in modulating the interactome and SUMOylome of Chlamydomonas reinhardtii

Translocation of channelrhodopsins (ChRs) is mediated by the intraflagellar transport (IFT) machinery. However, the functional role of the network involving photoreceptors, IFT and other proteins in controlling algal ciliary motility is still not fully delineated. In the current study, we have identified two important motifs at the C-terminus of ChR1, VXPX and LKNE. VXPX is a known ciliary targeting sequence in animals, and LKNE is a well-known SUMOylation motif. To the best of our knowledge, this study gives prima facie insight into the role of SUMOylation in Chlamydomonas. We prove that VMPS of ChR1 is important for interaction with GTPase CrARL11. We show that SUMO motifs are present in the C-terminus of putative ChR1s from green algae. Performing experiments with n-Ethylmaleimide (NEM) and Ubiquitin-like protease 1 (ULP-1) we show that SUMOylation may modulate ChR1 protein in Chlamydomonas. Experiments with 2D08, a known sumoylation blocker, increased the concentration of ChR1 protein. Finally, we show the endogenous SUMOylated proteins (SUMOylome) of C. reinhardtii, identified by using immunoprecipitation followed by nano-LC-MS/MS detection. This report establishes a link between evolutionarily conserved SUMOylation, and ciliary machinery for the maintenance and functioning of cilia across the eukaryotes. Our enriched SUMOylome of C. reinhardtii comprehends the proteins related to ciliary development and, photo-signaling, along with orthologue(s) associated to human ciliopathies as SUMO targets.

The integration of reactive oxygen species (ROS) and calcium signalling in abiotic stress responses

Reactive oxygen species (ROS) and calcium (Ca²⁺ ) signalling are interconnected in the perception and transmission of environmental signals that control plant growth, development and defence. The concept that systemically propagating Ca²⁺ and ROS waves function together with electric signals in directional cell-to-cell systemic signalling and even plant-to-plant communication, is now firmly imbedded in the literature. However, relatively few mechanistic details are available regarding the management of ROS and Ca²⁺ signals at the molecular level, or how synchronous and independent signalling might be achieved in different cellular compartments. This review discusses the proteins that may serve as nodes or connecting bridges between the different pathways during abiotic stress responses, highlighting the crosstalk between ROS and Ca²⁺ pathways in cell signalling. We consider putative molecular switches that connect these signalling pathways and the molecular machinery that achieves the synergistic operation of ROS and Ca²⁺ signals.

Glutamate receptor like channels: Emerging players in calcium mediated signaling in plants

Glutamate receptors like channels (GLRs) are ligand gated non-selective cation channels and are multigenic in nature. They are homologs of mammalian ionic glutamate receptors (iGLRs) that play an important role in neurotransmission. It has been more than 25 years of discovery of plant GLRs, since then, significant progress has been made to unravel their structure and function in plants. Recently, the first crystal structure of plant GLR has been resolved that suggests that, though, plant GLRs contain the conserved signature domains of iGLRs, their unique features enable agonist/antagonist-dependent change in their activity. GLRs exhibit diverse subcellular localization and undergo dynamic expression variation in response to developmental and environmental stress conditions in plants. The combined use of genetic, electrophysiology and calcium imaging using different genetically encoded calcium indicators has revealed that GLRs are involved in generating calcium (Ca²⁺) influx across the plasma membrane and are involved in shaping the Ca²⁺ signature in response to different developmental and environmental stimuli. These findings indicate that GLRs influence cytosolic Ca²⁺ dynamics, thus, highlighting "GLR-Ca²⁺-crosstalk (GCC)" in developmental and stress-responsive signaling pathways. With this background, the present review summarises the recent developments pertaining to GLR function, in the broader context of regulation of stress tolerance in plants.

Role of calcium sensor protein module CBL-CIPK in abiotic stress and light signaling responses in green algae

Ca²⁺ signaling is an important biological process that enable to perceive and communicate information in the cell. Our current understanding of the signaling system suggests that plants and animals have certain differences in signal-sensing mechanisms. The Ca²⁺-mediated CBL-CIPK module has emerged as a major sensor responder network for Ca²⁺ signaling and has been speculated to be involved in plant terrestrial life adaptation. This module has previously been reported in Archaeplastids, Chromalveolates, and Excavates. In our experimental analysis of Chlamydomonas reinhardtii CBLs, we proved that the CrCBL1 protein interacts with Phototropin and Channelrhodopsin, and the expression of CrCBLs is modulated by light. Further analysis using chlorophyte and streptophyte algal sequences allowed us to identify the differences that have evolved in CBL and CIPK proteins since plants have progressed from aquatic to terrestrial habitats. Moreover, an investigation of Klebsormidium CBL and CIPK genes led us to know that they are abiotic stress stimuli-responsive, indicating that their role was defined very early during terrestrial adaptations. Structure-based prediction and Ca²⁺-binding assays indicated that the KnCBL1 protein in Klebsormidium showed a typical Ca²⁺-binding pocket. In summary, the results of this study suggest that these stress-responsive proteins enable crosstalk between Ca²⁺ and light signaling pathways very early during plant adaptation from aquatic to terrestrial habitats.

Protein phosphatases and their targets: Comprehending the interactions in plant signaling pathways

Protein phosphorylation is a vital reversible post-translational modification. This process is established by two classes of enzymes: protein kinases and protein phosphatases. Protein kinases phosphorylate proteins while protein phosphatases dephosphorylate phosphorylated proteins, thus, functioning as 'critical regulators' in signaling pathways. The eukaryotic protein phosphatases are classified as phosphoprotein phosphatases (PPP), metallo-dependent protein phosphatases (PPM), protein tyrosine (Tyr) phosphatases (PTP), and aspartate (Asp)-dependent phosphatases. The PPP and PPM families are serine (Ser)/threonine (Thr) specific phosphatases (STPs) that dephosphorylate Ser and Thr residues. The PTP family dephosphorylates Tyr residues while dual-specificity phosphatases (DsPTPs/DSPs) dephosphorylate Ser, Thr, and Tyr residues. The composition of these enzymes as well as their substrate specificity are important determinants of their functional significance in a number of cellular processes and stress responses. Their role in animal systems is well-understood and characterized. The functional characterization of protein phosphatases has been extensively covered in plants, although the comprehension of their mechanistic basis is an ongoing pursuit. The nature of their interactions with other key players in the signaling process is vital to our understanding. The substrates or targets determine their potential as well as magnitude of the impact they have on signaling pathways. In this article, we exclusively overview the various substrates of protein phosphatases in plant signaling pathways, which are a critical determinant of the outcome of various developmental and stress stimuli.

Identification of Gene Copy Number in the Transgenic Plants by Quantitative Polymerase Chain Reaction (qPCR)

Transgenic events are defined as exogenous DNA insertion in the genome through genetic transformation. It is a powerful means for the improvement of crop plants and to understand the gene function. Multiple DNA insertion events may occur at one or several chromosomal locations. One of the important tasks, after validation of the transformation of transgenic plants, is the identification of single copy in the transgenic. This means the insertion of exogenous DNA fragment only in a single locus in the genome. Southern blot hybridization is a convincing and reliable method, for estimation of copy number in transgenic lines but it is cumbersome and time-consuming process. One of the other well-known methods is quantitative polymerase chain reactions (qPCR), a simple and rapid method to identify copy number from a population of independent transgenic lines. In comparison to the Southern hybridization method, qPCR is simpler to perform, requires less DNA, lesser time and does not require any labeled probes. This method utilizes specific primers to amplify target transgenes and endogenous reference genes. Designing an appropriate and specific primer pair is a very crucial part of the estimation of the gene copy number. In this chapter, we have illustrated a detailed methodology for identification of the gene copy of the transgenic plants.

CIPK9 targets VDAC3 and modulates oxidative stress responses in Arabidopsis

Calcium (Ca²⁺ ) is widely recognized as a key second messenger in mediating various plant adaptive responses. Here we show that calcineurin B-like interacting protein kinase CIPK9 along with its interacting partner VDAC3 identified in the present study are involved in mediating plant responses to methyl viologen (MV). CIPK9 physically interacts with and phosphorylates VDAC3. Co-localization, co-immunoprecipitation, and fluorescence resonance energy transfer experiments proved their physical interaction in planta. Both cipk9 and vdac3 mutants exhibited a tolerant phenotype against MV-induced oxidative stress, which coincided with the lower-level accumulation of reactive oxygen species in their roots. In addition, the analysis of cipk9vdac3 double mutant and VDAC3 overexpressing plants revealed that CIPK9 and VDAC3 were involved in the same pathway for inducing MV-dependent oxidative stress. The response to MV was suppressed by the addition of lanthanum chloride, a non-specific Ca²⁺ channel blocker indicating the role of Ca²⁺ in this pathway. Our study suggest that CIPK9-VDAC3 module may act as a key component in mediating oxidative stress responses in Arabidopsis.

Delineating Calcium Signaling Machinery in Plants: Tapping the Potential through Functional Genomics

Plants have developed calcium (Ca²⁺) signaling as an important mechanism of  regulation of  stress perception,  developmental cues, and  responsive gene  expression. The  post-genomic era has witnessed the successful unravelling of the functional characterization of genes and the creation of large datasets of molecular information. The major elements of Ca²⁺ signaling machinery include Ca²⁺ sensors and responders such as Calmodulins (CaMs), Calmodulin-like proteins (CMLs), Ca²⁺/CaM-dependent protein kinases (CCaMKs), Ca²⁺-dependent protein kinases (CDPKs), Calcineurin B-like proteins (CBLs) as well as transporters, such as Cyclic nucleotide-gated channels (CNGCs), Glutamate-like receptors (GLRs), Ca²⁺-ATPases, Ca²⁺/H⁺ exchangers (CAXs) and mechanosensitive channels. These elements play an important role in the regulation of physiological processes and plant responses to various stresses. Detailed genomic analysis can help us in the identification of potential molecular targets that can be exploited towards the development of stress-tolerant crops. The information sourced from model systems through omics approaches helps in the prediction and simulation of regulatory networks involved in responses to different stimuli at the molecular and cellular levels. The molecular delineation of Ca²⁺ signaling pathways could be a stepping stone for engineering climate-resilient crop plants. Here, we review the recent developments in Ca²⁺ signaling in the context of transport, responses, and adaptations significant for crop improvement through functional genomics approaches.

Ectopic expression of finger millet calmodulin confers drought and salinity tolerance in Arabidopsis thaliana

Overexpression of finger millet calmodulin imparts drought and salt tolerance in plants. Drought and salinity are major environmental stresses which affect crop productivity and therefore are major hindrance in feeding growing population world-wide. Calcium (Ca²⁺) signaling plays a crucial role during the plant's response to these stress stimuli. Calmodulin (CaM), a crucial Ca²⁺sensor, is involved in transducing the signal downstream in various physiological, developmental and stress responses by modulating a plethora of target proteins. The role of CaM has been well established in the model plant Arabidopsis thaliana for regulating various developmental processes, stress signaling and ion transport. In the current study, we investigate the CaM of Eleusine coracana (common name finger millet, known especially for its drought tolerance and superior Ca²⁺ content). In-silico analysis showed that Eleusine CaM (EcCaM) has greater similarity to rice CaM as compared to Arabidopsis CaM due to the presence of highly conserved four EF-hand domains. To decipher the in-planta function of EcCaM, we have adopted the gain-of-function approach by generating the 35S::EcCaM over-expression transgenic in Arabidopsis. Overexpression of EcCaM in Arabidopsis makes the plant tolerant to polyethylene glycol (PEG) induced drought and salt stress (NaCl) as demonstrated by post-germination based phenotypic assay, ion leakage, MDA and proline estimation, ROS detection under stressed and normal conditions. Moreover, EcCaM overexpression leads to hypersensitivity toward exogenously applied ABA at the seed germination stage. These findings reveal that EcCaM mediates tolerance to drought and salinity stress. Also, our results indicate that EcCaM is involved in modulating ABA signaling. Summarizing our results, we report for the first time that EcCaM is involved in modulating plants response to stress and this information can be used for the generation of future-ready crops that can tolerate a wide range of abiotic stresses.

Ca2+-CBL-CIPK: a modulator system for efficient nutrient acquisition

Calcium (Ca²⁺) is a universal second messenger essential for the growth and development of plants in normal and stress situations. In plants, the proteins, CBL (calcineurin B-like) and CIPK (CBL-interacting protein kinase), form one of the important Ca²⁺ decoding complexes to decipher Ca²⁺ signals elicited by environmental challenges. Multiple interactors distinguish CBL and CIPK protein family members to form a signaling network for regulated perception and transduction of environmental signals, e.g., signals generated under nutrient stress conditions. Conservation of equilibrium in response to varying soil nutrient status is an important aspect for plant vigor and yield. Signaling processes have been reported to observe nutrient fluctuations as a signal responsible for regulated nutrient transport adaptation. Recent studies have identified downstream targets of CBL-CIPK modules as ion channels or transporters and their association in signaling nutrient disposal including potassium, nitrate, ammonium, magnesium, zinc, boron, and iron. Ca²⁺-CBL-CIPK pathway modulates ion transporters/channels and hence maintains a homeostasis of several important plant nutrients in the cytosol and sub-cellular compartments. In this article, we summarize recent literature to discuss the role of the Ca²⁺-CBL-CIPK pathway in cellular osmoregulation and homeostasis on exposure to nutrient excess or deprived soils. This further establishes a link between taking up the nutrient in the roots and its distribution and homeostasis during the generation of signal for the development and survival of plants.

VDACs: An Outlook on Biochemical Regulation and Function in Animal and Plant Systems

The voltage-dependent anion channels (VDACs) are the most abundant proteins present on the outer mitochondrial membrane. They serve a myriad of functions ranging from energy and metabolite exchange to highly debatable roles in apoptosis. Their role in molecular transport puts them on the center stage as communicators between cytoplasmic and mitochondrial signaling events. Beyond their general role as interchangeable pores, members of this family may exhibit specific functions. Even after nearly five decades of their discovery, their role in plant systems is still a new and rapidly emerging field. The information on biochemical regulation of VDACs is limited. Various interacting proteins and post-translational modifications (PTMs) modulate VDAC functions, amongst these, phosphorylation is quite noticeable. In this review, we have tried to give a glimpse of the recent advancements in the biochemical/interactional regulation of plant VDACs. We also cover a critical analysis on the importance of PTMs in the functional regulation of VDACs. Besides, the review also encompasses numerous studies which can identify VDACs as a connecting link between Ca2+ and reactive oxygen species signaling in special reference to the plant systems.

Plant protein phosphatases: What do we know about their mechanism of action?

Protein phosphorylation is a major reversible post-translational modification. Protein phosphatases function as 'critical regulators' in signaling networks through dephosphorylation of proteins, which have been phosphorylated by protein kinases. A large understanding of their working has been sourced from animal systems rather than the plant or the prokaryotic systems. The eukaryotic protein phosphatases include phosphoprotein phosphatases (PPP), metallo-dependent protein phosphatases (PPM), protein tyrosine (Tyr) phosphatases (PTP), and aspartate (Asp)-dependent phosphatases. The PPP and PPM families are serine(Ser)/threonine(Thr)-specific phosphatases (STPs), while PTP family is Tyr specific. Dual-specificity phosphatases (DsPTPs/DSPs) dephosphorylate Ser, Thr, and Tyr residues. PTPs lack sequence homology with STPs, indicating a difference in catalytic mechanisms, while the PPP and PPM families share a similar structural fold indicating a common catalytic mechanism. The catalytic cysteine (Cys) residue in the conserved HCX₅ R active site motif of the PTPs acts as a nucleophile during hydrolysis. The PPP members require metal ions, which coordinate the phosphate group of the substrate, followed by a nucleophilic attack by a water molecule and hydrolysis. The variable holoenzyme assembly of protein phosphatase(s) and the overlap with other post-translational modifications like acetylation and ubiquitination add to their complexity. Though their functional characterization is extensively reported in plants, the mechanistic nature of their action is still being explored by researchers. In this review, we exclusively overview the plant protein phosphatases with an emphasis on their mechanistic action as well as structural characteristics.

VDAC and its interacting partners in plant and animal systems: an overview

Molecular trafficking between different subcellular compartments is the key for normal cellular functioning. Voltage-dependent anion channels (VDACs) are small-sized proteins present in the outer mitochondrial membrane, which mediate molecular trafficking between mitochondria and cytoplasm. The conductivity of VDAC is dependent on the transmembrane voltage, its oligomeric state and membrane lipids. VDAC acts as a convergence point to a diverse variety of mitochondrial functions as well as cell survival. This functional diversity is attained due to their interaction with a plethora of proteins inside the cell. Although, there are hints toward functional conservation/divergence between animals and plants; knowledge about the functional role of the VDACs in plants is still limited. We present here a comparative overview to provide an integrative picture of the interactions of VDAC with different proteins in both animals and plants. Also discussed are their physiological functions from the perspective of cellular movements, signal transduction, cellular fate, disease and development. This in-depth knowledge of the biological importance of VDAC and its interacting partner(s) will assist us to explore their function in the applied context in both plant and animal.

Arabidopsis Mitochondrial Voltage-Dependent Anion Channels Are Involved in Maintaining Reactive Oxygen Species Homeostasis, Oxidative and Salt Stress Tolerance in Yeast

Voltage-dependent anion channels (VDACs) are conserved proteins of the mitochondria. We have functionally compared Arabidopsis VDACs using Saccharomyces cerevisiae Δpor1 and M3 yeast system. VDAC (1, 2, and 4) were able to restore Δpor1 growth in elevated temperature, in oxidative and salt stresses, whereas VDAC3 only partially rescued Δpor1 in these conditions. The ectopic expression of VDAC (1, 2, 3, and 4) in mutant yeast recapitulated the mitochondrial membrane potential thus, enabled it to maintain reactive oxygen species homeostasis. Overexpression of these VDACs (AtVDACs) in M3 strain did not display any synergistic or antagonistic activity with the native yeast VDAC1 (ScVDAC1). Collectively, our data suggest that Arabidopsis VDACs are involved in regulating respiration, reactive oxygen species homeostasis, and stress tolerance in yeast.

Emerging concepts of potassium homeostasis in plants

Potassium (K+) is an essential cation in all organisms that influences crop production and ecosystem stability. Although most soils are rich in K minerals, relatively little K+ is present in forms that are available to plants. Moreover, leaching and run-off from the upper soil layers contribute to K+ deficiencies in agricultural soils. Hence, the demand for K fertilizer is increasing worldwide. K+ regulates multiple processes in cells and organs, with K+ deficiency resulting in decreased plant growth and productivity. Here, we discuss the complexity of the reactive oxygen species-calcium-hormone signalling network that is responsible for the sensing of K+ deficiency in plants, together with genetic approaches using K+ transporters that have been used to increase K+ use efficiency (KUE) in plants, particularly under environmental stress conditions such as salinity and heavy metal contamination. Publicly available rice transcriptome data are used to demonstrate the two-way relationship between K+ and nitrogen nutrition, highlighting how each nutrient can regulate the uptake and root to shoot translocation of the other. Future research directions are discussed in terms of this relationship, as well as prospects for molecular approaches for the generation of improved varieties and the implementation of new agronomic practices. An increased knowledge of the systems that sense and take up K+, and their regulation, will not only improve current understanding of plant K+ homeostasis but also facilitate new research and the implementation of measures to improve plant KUE for sustainable food production.

PP2A Phosphatases Take a Giant Leap in the Post-Genomics Era

BACKGROUND

Protein phosphorylation is an important reversible post-translational modifica-tion, which regulates a number of critical cellular processes. Phosphatases and kinases work in a con-certed manner to act as a "molecular switch" that turns-on or - off the regulatory processes driving the growth and development under normal circumstances, as well as responses to multiple stresses in plant system. The era of functional genomics has ushered huge amounts of information to the framework of plant systems. The comprehension of who's who in the signaling pathways is becoming clearer and the investigations challenging the conventional functions of signaling components are on a rise. Protein phosphatases have emerged as key regulators in the signaling cascades. PP2A phosphatases due to their diverse holoenzyme compositions are difficult to comprehend.

CONCLUSION

In this review, we highlight the functional versatility of PP2A members, deciphered through the advances in the post-genomic era.

A protein phosphatase 2C, AP2C1, interacts with and negatively regulates the function of CIPK9 under potassium-deficient conditions in Arabidopsis

Potassium (K+) is a major macronutrient required for plant growth. An adaptive mechanism to low-K+ conditions involves activation of the Ca2+ signaling network that consists of calcineurin B-like proteins (CBLs) and CBL-interacting kinases (CIPKs). The CBL-interacting protein kinase 9 (CIPK9) has previously been implicated in low-K+ responses in Arabidopsis thaliana. Here, we report a protein phosphatase 2C (PP2C), AP2C1, that interacts with CIPK9. Fluorescence resonance energy transfer (FRET), bimolecular fluorescence complementation (BiFC), and co-localization analyses revealed that CIPK9 and AP2C1 interact in the cytoplasm. AP2C1 dephosphorylates the auto-phosphorylated form of CIPK9 in vitro, presenting a regulatory mechanism for CIPK9 function. Furthermore, genetic and molecular analyses revealed that ap2c1 null mutants (ap2c1-1 and ap2c1-2) are tolerant to low-K+ conditions, retain higher K+ content, and show higher expression of K+-deficiency related genes contrary to cipk9 mutants (cipk9-1 and cipk9-2). In contrast, transgenic plants overexpressing AP2C1 were sensitive to low-K+ conditions. Thus, this study shows that AP2C1 and CIPK9 interact to regulate K+-deficiency responses in Arabidopsis. CIPK9 functions as positive regulator whereas AP2C1 acts as a negative regulator of Arabidopsis root growth and seedling development under low-K+ conditions.

Rice phytoglobins regulate responses under low mineral nutrients and abiotic stresses in Arabidopsis thaliana

Just like animals, plants also contain haemoglobins (known as phytoglobins in plants). Plant phytoglobins (Pgbs) have been categorized into 6 different classes, namely, Phytogb0 (Pgb0), Phytogb1 (Pgb1), Phytogb2 (Pgb2), SymPhytogb (sPgb), Leghaemoglobin (Lb), and Phytogb3 (Pgb3). Among the 6 Phytogbs, sPgb and Lb have been functionally characterized, whereas understanding of the roles of other Pgbs is still evolving. In our present study, we have explored the function of 2 rice Pgbs (OsPgb1.1 and OsPgb1.2). OsPgb1.1, OsPgb1.2, OsPgb1.3, and OsPgb1.4 displayed increased level of transcript upon salt, drought, cold, and ABA treatment. The overexpression (OX) lines of OsPgb1.2 in Arabidopsis showed a tolerant phenotype in terms of better root growth in low potassium (K+ ) conditions. The expression of the known K+ gene markers such as LOX2, HAK5, and CAX3 was much higher in the OsPgb1.2 OX as compared to wild type. Furthermore, the OsPgb1.2 OX lines showed a decrease in reactive oxygen species (ROS) production and conversely an increase in the K+ content, both in root and shoot, as compared to wild type in K+ limiting condition. Our results indicated the potential involvement of OsPgb1.2 in signalling networks triggered by the nutrient deficiency stresses.

The unc-53 gene negatively regulates rac GTPases to inhibit unc-5 activity during Distal tip cell migrations in C. elegans

The unc-53/NAV2 gene encodes for an adaptor protein required for cell migrations along the anteroposterior (AP) axes of C. elegans. This study identifies unc-53 as a novel component of signaling pathways regulating Distal tip cell (DTC) migrations along the AP and dorsoventral (DV) axes. unc-53 negatively regulates and functions downstream of ced-10/Rac pathway genes; ced-10/Rac and mig-2/RhoG, which are required for proper DTC migration. Moreover, unc-53 exhibits genetic interaction with abl-1 and unc-5, the 2 known negative regulators of ced-10/Rac signaling. Our genetic analysis supports the model, where abl-1 negatively regulates unc-53 during DTC migrations and requirement of unc-53 function during both AP and DV DTC migrations could be due to unc-53 mediated regulation of unc-5 activity.

Heterologous expression of GmSIP1;3 from soybean in tobacco showed and growth retardation and tolerance to hydrogen peroxide

Aquaporins (AQPs) are transmembrane protein channels that are members of Major Intrinsic Proteins (MIP) superfamily. AQPs play important roles in plant reproduction, cell elongation, osmoregulation, influence leaf physiology and are responsive to drought and salt tolerance. Small intrinsic proteins (SIPs)belongs to one of the groups of AQPs, which are mainly localized to endoplasmic reticulum(ER). While this group of aquaporin is being well studied in Arabidopsis, grape and other plant species, not much is known about the molecular regulatory mechanisms driven by ER-type AQPs in Glycine Max. In this study, the function of GmSIP1;3 is studied in detail by using both yeast and plant systems. GmSIP1;3 showed a ubiquitous expression pattern in all different tissues in Glycine Max. Heterologous expression of GmSIP1;3 in Nicotiana tabacum conferred a short root phenotype,growth retardation at seedling stage and significant tolerance to oxidative stress (H2O2) both in yeast and plant systems. Auxin (IAA) content significantly increased in transgenic plants compared with that of wild type, however, the abscisic acid (ABA) content was significantly reduced. Subcellular localization and colocalization analyses showed GmSIP1;3 localized to ER plasma membrane. On the basis of these observations, we postulate that GmSIP1;3 is involved in oxidative stress pathways.

Recent Advances in Substrate Identification of Protein Kinases in Plants and Their Role in Stress Management

Protein phosphorylation-dephosphorylation is a well-known regulatory mechanism in biological systems and has become one of the significant means of protein function regulation, modulating most of the biological processes. Protein kinases play vital role in numerous cellular processes. Kinases transduce external signal into responses such as growth, immunity and stress tolerance through phosphorylation of their target proteins. In order to understand these cellular processes at the molecular level, one needs to be aware of the different substrates targeted by protein kinases. Advancement in tools and techniques has bestowed practice of multiple approaches that enable target identification of kinases. However, so far none of the methodologies has been proved to be as good as a panacea for the substrate identification. In this review, the recent advances that have been made in the identifications of putative substrates and the implications of these kinases and their substrates in stress management are discussed.

Genome-wide identification of Major Intrinsic Proteins in Glycine soja and characterization of GmTIP2;1 function under salt and water stress

In different plant species, aquaporins (AQPs) facilitate water movement by regulating root hydraulic conductivity under diverse stress conditions such as salt and water stresses. To improve survival and yield of crop plants, a detailed understanding of stress responses is imperative and required. We used Glycine soja genome as a tool to study AQPs, considering it shows abundant genetic diversity and higher salt environment tolerance features and identified 62 Gs AQP genes. Additionally, this study identifies major aquaporins responsive to salt and drought stresses in soybean and elucidates their mode of action through yeast two-hybrid assay and BiFC. Under stress condition, the expression analysis of AQPs in roots and leaves of two contrasting ecotypes of soybean revealed diverse expression patterns suggesting complex regulation at transcriptional level. Based on expression analysis, we identify GmTIP2;1 as a potential candidate involved in salinity and drought responses. The overexpression of GmTIP2;1 in Saccharomyces cerevisiae as well as in-planta enhanced salt and drought tolerance. We identified that GmTIP2;1 forms homodimers as well as interacts with GmTIP1;7 and GmTIP1;8. This study augments our knowledge of stress responsive pathways and also establishes GmTIP2;1 as a new stress responsive gene in imparting salt stress tolerance in soybean.

Arabidopsis CBL interacting protein kinase 3 interacts with ABR1, an APETALA2 domain transcription factor, to regulate ABA responses

Calcium (Ca²⁺) plays a vital role as a second messenger in several signaling pathways in plants. The calcineurin B-like proteins (CBLs) represent a family of plant calcium-binding proteins that function in propagating Ca²⁺ signals by interacting with CBL interacting protein kinases (CIPKs). Phosphorylation of CBL by CIPK is essential for the module to display full activity towards its target protein. Previous genetic analysis showed that the function of CBL9-CIPK3 module was implicated in negatively regulating seed germination and early development. In the present study, we have biochemically investigated the interaction of CBL9-CIPK3 module and our findings show that CBL9 is phosphorylated by CIPK3. Moreover, Abscisic acid repressor 1 (ABR1) is identified as the downstream target of CIPK3 and CIPK3-ABR1 function to regulate ABA responses during seed germination. Our study also indicates that the role of ABR1 is not limited to seed germination but it also regulates the ABA dependent processes in the adult stage of plant development. Combining our results, we conclude that the CBL9-CIPK3-ABR1 pathway functions to regulate seed germination and ABA dependent physiological processes in Arabidopsis.

Alternative Splicing of CIPK3 Results in Distinct Target Selection to Propagate ABA Signaling in Arabidopsis

Calcium (Ca²⁺) signaling is pivotal in transmission of information in the cell. Various Ca²⁺ sensing molecules work to sense and relay the encrypted messages to the intended targets in the cell to maintain this signal transduction. CBL-interacting protein kinases (CIPKs) are crucial components of Ca²⁺ signal transduction during various abiotic stresses. Although there are intron rich CIPKs in the plant genome but very little has been reported about their alternative splicing. Moreover the physiological significance of this event in the Ca²⁺ signaling is still elusive. Therefore in this study, we have selected CIPK3, which has highest number of splice variants amongst Arabidopsis CIPKs. Expression profiling of five splice variants of CIPK3 by qRT-PCR in four Arabidopsis thaliana ecotypes revealed preferential transcript accumulation but similar subcellular localization of the variants and interaction with similar CBLs. ABA and drought treatment resulted in the higher accumulation of the alternately spliced transcripts of CIPK3 in Arabidopsis ecotype Wassilewkija. The transcripts of CIPK3.1 and CIPK3.4 are relatively more induced compared to other alternative splice variants. Out of four splice variants studied, we found CIPK3.1 and CIPK3.2 showing preference for ABR1, a previously reported interactor of CIPK3. We conclude that the differential expression and choice of downstream partner by CIPK3-splice variants might be one of the mechanisms of Ca²⁺ mediated preferential regulation of ABA and other stress signals.

Plant Stress Responses Mediated by CBL-CIPK Phosphorylation Network

At any given time and location, plants encounter a flood of environmental stimuli. Diverse signal transduction pathways sense these stimuli and generate a diverse array of responses. Calcium (Ca²⁺) is generated as a second messenger due to these stimuli and is responsible for transducing the signals downstream in the pathway. A large number of Ca²⁺ sensor-responder components are responsible for Ca²⁺ signaling in plants. The sensor-responder complexes calcineurin B-like protein (CBL) and CBL-interacting protein kinases (CIPKs) are pivotal players in Ca²⁺-mediated signaling. The CIPKs are the protein kinases and hence mediate signal transduction mainly by the process of protein phosphorylation. Elaborate studies conducted in Arabidopsis have shown the involvement of CBL-CIPK complexes in abiotic and biotic stresses, and nutrient deficiency. Additionally, studies in crop plants have also indicated their role in the similar responses. In this chapter, we review the current literature on the CBL and CIPK network, shedding light into the enzymatic property and mechanism of action of CBL-CIPK complexes. We also summarize various reports on the functional modulation of the downstream targets by the CBL-CIPK modules across all plant species.

Role of Cyclic Nucleotide Gated Channels in Stress Management in Plants

Tolerance of plants to a number of biotic and abiotic stresses such as pathogen and herbivore attack, drought, salinity, cold and nutritional limitations is ensued by complex multimodule signaling pathways. The outcome of this complex signaling pathways results in adaptive responses by restoring the cellular homeostasis and thus promoting survival. Functions of many plant cation transporter and channel protein families such as glutamate receptor homologs (GLRs), cyclic nucleotide-gated ion channel (CNGC) have been implicated in providing biotic and abiotic stress tolerance. Ion homeostasis regulated by several transporters and channels is one of the crucial parameters for the optimal growth, development and survival of all living organisms. The CNGC family members are known to be involved in the uptake of cations such as Na(+), K(+) and Ca(2+) and regulate plant growth and development. Detail functional genomics approaches have given an emerging picture of CNGCs wherein these protein are believed to play crucial role in pathways related to cellular ion homeostasis, development and as a 'guard' in defense against biotic and abiotic challenges. Here, we discuss the current knowledge of role of CNGCs in mediating stress management and how they aid plants in survival under adverse conditions.

The LIKE SEX FOUR2 regulates root development by modulating reactive oxygen species homeostasis in Arabidopsis

Maintaining reactive oxygen species (ROS) homeostasis plays a central role in plants, and is also critical for plant root development. Threshold levels of ROS act as signals for elongation and differentiation of root cells. The protein phosphatase LIKE SEX FOUR2 (LSF2) has been reported to regulate starch metabolism in Arabidopsis, but little is known about the mechanism how LSF2 affect ROS homeostasis. Here, we identified that LSF2 function as a component modulating ROS homeostasis in response to oxidative stress and, thus regulate root development. Compared with wild type Arabidopsis, lsf2-1 mutant exhibited reduced rates of superoxide generation and higher levels of hydrogen peroxide upon oxidative stress treatments. The activities of several antioxidant enzymes, including superoxide dismutase, catalase, and ascorbate peroxidase, were also affected in lsf2-1 mutant under these oxidative stress conditions. Consequently, lsf2-1 mutant exhibited the reduced root growth but less inhibition of root hair formation compared to wild type Arabidopsis plants. Importantly, protein phosphatase LSF2 interacted with mitogen-activated protein kinase 8 (MPK8), a known component of ROS homeostasis pathways in the cytoplasm. These findings indicated the novel function of LSF2 that controls ROS homeostasis to regulate root development.

Corrigendum: Emerging Roles of Strigolactones in Plant Responses to Stress and Development

[This corrects the article on p. 434 in vol. 7, PMID: 27092155.].

Emerging Roles of Strigolactones in Plant Responses to Stress and Development

Our environment constantly undergoes changes either natural or manmade affecting growth and development of all the organisms including plants. Plants are sessile in nature and therefore to counter environmental changes such as light, temperature, nutrient and water availability, pathogen, and many others; plants have evolved intricate signaling mechanisms, composed of multiple components including several plant hormones. Research conducted in the last decade has placed Strigolactones (SLs) in the growing list of plant hormones involved in coping with environmental changes. SLs are carotenoid derivatives functioning as both endogenous and exogenous signaling molecules in response to various environmental cues. Initially, SLs were discovered as compounds that are harmful to plants due to their role as stimulants in seed germination of parasitic plants, a more beneficial role in plant growth and development was uncovered much later. SLs are required for maintaining plant architecture by regulating shoot and root growth in response to various external stimuli including arbuscular mycorrhizal fungi, light, nutrients, and temperature. Moreover, a role for SLs has also been recognized during various abiotic and biotic stress conditions making them suitable target for generating genetically engineered crop plants with improved yield. This review discusses the biosynthesis of SLs and their regulatory and physiological roles in various stress conditions. Understanding of detailed signaling mechanisms of SLs will be an important factor for designing genetically modified crops for overcoming the problem of crop loss under stressful conditions.

A rice tonoplastic calcium exchanger, OsCCX2 mediates Ca2+/cation transport in yeast

In plant cell, cations gradient in cellular compartments is maintained by synergistic action of various exchangers, pumps and channels. The Arabidopsis exchanger family members (AtCCX3 and AtCCX5) were previously studied and belong to CaCA (calcium cation exchangers) superfamily while none of the rice CCXs has been functionally characterized for their cation transport activities till date. Rice genome encode four CCXs and only OsCCX2 transcript showed differential expression under abiotic stresses and Ca(2+) starvation conditions. The OsCCX2 localized to tonoplast and suppresses the Ca(2+) sensitivity of K667 (low affinity Ca(2+) uptake deficient) yeast mutant under excess CaCl2 conditions. In contrast to AtCCXs, OsCCX2 expressing K667 yeast cells show tolerance towards excess Na(+), Li(+), Fe(2+), Zn(2+) and Co(2+) and suggest its ability to transport both mono as well as divalent cations in yeast. Additionally, in contrast to previously characterized AtCCXs, OsCCX2 is unable to complement yeast trk1trk2 double mutant suggesting inability to transport K(+) in yeast system. These finding suggest that OsCCX2 having distinct metal transport properties than previously characterized plant CCXs. OsCCX2 can be used as potential candidate for enhancing the abiotic stress tolerance in plants as well as for phytoremediation of heavy metal polluted soil.

The CBL-CIPK signaling module in plants: a mechanistic perspective

In a given environment, plants are constantly exposed to multitudes of stimuli. These stimuli are sensed and transduced to generate a diverse array of responses by several signal transduction pathways. Calcium (Ca²⁺ ) signaling is one such important pathway involved in transducing a large number of stimuli or signals in both animals and plants. Ca²⁺ engages a plethora of decoders to mediate signaling in plants. Among these groups of decoders, the sensor responder complex of calcineurin B-like protein (CBL) and CBL-interacting protein kinases (CIPKs) play a very significant role in transducing these signals. The signal transduction mechanism in most cases is phosphorylation events, but some structural role for the pair has also come to light recently. In this review, we discuss the structural nature of the sensor-responder duo; their mechanism of substrate phosphorylation and also their structural role in modulating targets. Moreover, the mechanism of complex formation and mechanistic role of protein phosphatases with CBL-CIPK module has been mentioned. A comparison of CBL-CIPK with other decoders of Ca²⁺ signaling in plants also signifies the relatedness and diversity in signaling pathways. Further an attempt has been made to compare this aspect of Ca²⁺ signaling pathways in different plant species to develop a holistic understanding of conservation of stimulus-response-coupling mediated by this Ca²⁺ -CBL-CIPK module.

Calcineurin B-Like Protein-Interacting Protein Kinase CIPK21 Regulates Osmotic and Salt Stress Responses in Arabidopsis

The role of calcium-mediated signaling has been extensively studied in plant responses to abiotic stress signals. Calcineurin B-like proteins (CBLs) and CBL-interacting protein kinases (CIPKs) constitute a complex signaling network acting in diverse plant stress responses. Osmotic stress imposed by soil salinity and drought is a major abiotic stress that impedes plant growth and development and involves calcium-signaling processes. In this study, we report the functional analysis of CIPK21, an Arabidopsis (Arabidopsis thaliana) CBL-interacting protein kinase, ubiquitously expressed in plant tissues and up-regulated under multiple abiotic stress conditions. The growth of a loss-of-function mutant of CIPK21, cipk21, was hypersensitive to high salt and osmotic stress conditions. The calcium sensors CBL2 and CBL3 were found to physically interact with CIPK21 and target this kinase to the tonoplast. Moreover, preferential localization of CIPK21 to the tonoplast was detected under salt stress condition when coexpressed with CBL2 or CBL3. These findings suggest that CIPK21 mediates responses to salt stress condition in Arabidopsis, at least in part, by regulating ion and water homeostasis across the vacuolar membranes.

Role of Protein Tyrosine Phosphatases in Plants

Reversible protein phosphorylation is a crucial regulatory mechanism that controls many biological processes in eukaryotes. In plants, phosphorylation events primarily occur on serine (Ser) and threonine (Thr) residues, while in certain cases, it was also discovered on tyrosine (Tyr) residues. In contrary to plants, extensive reports on Tyr phosphorylation regulating a large numbers of biological processes exist in animals. Despite of such prodigious function in animals, Tyr phosphorylation is a least studied mechanism of protein regulation in plants. Recently, various chemical analytical procedures have strengthened the view that Tyr phosphorylation is equally prevalent in plants as in animals. However, regardless of Tyr phosphorylation events occuring in plants, no evidence could be found for the existence of gene encoding for Tyr phosphorylation i.e. the typical Tyr kinases. Various methodologies have suggested that plant responses to stress signals and developmental processes involved modifications in protein Tyr phosphorylation. Correspondingly, various reports have established the role of PTPs (Protein Tyrosine Phosphatases) in the dephosphorylation and inactivation of mitogen activated protein kinases (MAPKs) hence, in the regulation of MAPK signaling cascade. Besides this, many dual specificity protein phosphatases (DSPs) are also known to bind starch and regulate starch metabolism through reversible phosphorylation. Here, we are emphasizing the significant progress on protein Tyr phosphatases to understand the role of these enzymes in the regulation of post-translational modification in plant physiology and development.

ABA inducible rice protein phosphatase 2C confers ABA insensitivity and abiotic stress tolerance in Arabidopsis

Arabidopsis PP2C belonging to group A have been extensively worked out and known to negatively regulate ABA signaling. However, rice (Oryza sativa) orthologs of Arabidopsis group A PP2C are scarcely characterized functionally. We have identified a group A PP2C from rice (OsPP108), which is highly inducible under ABA, salt and drought stresses and localized predominantly in the nucleus. Genetic analysis revealed that Arabidopsis plants overexpressing OsPP108 are highly insensitive to ABA and tolerant to high salt and mannitol stresses during seed germination, root growth and overall seedling growth. At adult stage, OsPP108 overexpression leads to high tolerance to salt, mannitol and drought stresses with far better physiological parameters such as water loss, fresh weight, chlorophyll content and photosynthetic potential (Fv/Fm) in transgenic Arabidopsis plants. Expression profile of various stress marker genes in OsPP108 overexpressing plants revealed interplay of ABA dependent and independent pathway for abiotic stress tolerance. Overall, this study has identified a potential rice group A PP2C, which regulates ABA signaling negatively and abiotic stress signaling positively. Transgenic rice plants overexpressing this gene might provide an answer to the problem of low crop yield and productivity during adverse environmental conditions.