Browsing by Author "Sagar, Sushma"

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Abscisic acid, a principal regulator of plant abiotic stress responses
(Elsevier B.V., 2019) Sagar, Sushma; Singh, Amarjeet
Plants are routinely troubled by various abiotic stresses such as high salinity, dehydration, and low temperature during their life span. These abiotic stresses have detrimental effect on plant development, longevity, and productivity. Plants have evolved with a sessile nature, and unlike animals, they cannot move away from adverse growth conditions. Rather, they are destined to combat these stress conditions in their stationary habitat. Therefore, plants have devised an adaptive mechanism that entails the activation of several signal transduction pathways, leading to diverse molecular, cellular, and physiological changes (Singh et al., 2016, 2018). Most signal transduction pathways triggered in response to biotic or abiotic stresses are mediated by one or more plant hormones. Therefore, plant hormones are a crucial player in regulating plants’ response to various environmental cues (Iqbal et al., 2017; Khan et al., 2015a,b; Khan and Khan, 2014; Kazan, 2015; Per et al., 2018). Generally, phytohormones like salicylic acid (SA), jasmonic acid (JAs), and ethylene (ET) are implicated in plant response to pathogens, wounding, and other biotic stresses, whereas gibberellins (GAs), auxins (IAAs), brassinosteroids (BRs), and cytokinins are known to regulate plant development. However, recent advancements in plant stress related research have shown that all plant hormones could control multiple plant processes and are involved in crosstalk of signaling pathways. For example, SA, JA, and ET, apart from biotic stresses, are also involved in plant development and responses to abiotic stresses. Similarly, auxins and GA are crucial in abiotic and biotic stress responses (Colebrook et al., 2014; Kazan, 2013; Khan and Khan, 2013; Santino et al., 2013). Abscisic acid (ABA) is the key hormone that primarily regulates plants’ responses to various abiotic stresses; however, like other phytohormones ABA is also known to regulate plants’ response to biotic stress and development (Singh et al., 2016). The discovery of the vital phytohormone ABA dates way back to the 1960s. Several independent and convergent experiments carried out by various research groups led to the discovery of ABA (Cracker and Abeles, 1969). However, the earliest and most convincing was the discovery of ABA in cotton, where it was involved in fruit abscission and dormancy (Li et al., 2017). As time and research progressed, newer functions of ABA were unveiled, including adaptation to various stresses, stomatal closure, sugar accumulation, seed development, etc. Due to its crucial role in abiotic and biotic stresses, ABA is known as a “stress hormone”. Plenty of research on ABA accumulated ample information on its biosynthesis, storage, catabolism, site of action, and its possible targets. During the last decade, the ABA receptors and their crystal structures have been elucidated (Ma et al., 2009; Park et al., 2009). This information has provided a clear cut paradigm of the ABA signal transduction pathway. Moreover, recruiting the combinations of different key players such as PP2C phosphatase and SnRK2 kinases has helped to understand the signal transduction pathway. Recent studies have provided newer insights into the functional roles of the ABA signaling cascade in various aspects of plant growth and development. In this chapter, we discuss different facets of ABA in plants, including its biosynthesis, catabolism, ABA signaling pathway and various signaling components, and the role of ABA in abiotic stresses and plant development.
Calcium dependent protein kinase, a versatile player in plant stress management and development
(Taylor & Francis Group, 2018) Singh, Amarjeet; Sagar, Sushma; Biswas, Dipul Kumar
Calcium-dependent protein kinases (CDPKs) form the major and unique group of calcium (Ca2+) sensors in plants. Attributed to their peculiar structural features, CDPKs play a dual role of “Ca2+ sensor and responder” and translate the message from specific Ca2+ signature to phosphorylation events. Most of the stress and developmental triggers instigate an increase in Ca2+ level and consequently Ca2+ signaling in plants. Expression and functional analyses across plant species have revealed differential regulation of CDPK transcripts, activity, protein interactions and substrate targeting under different cues, including biotic and abiotic stresses and plant development. Thus, vital roles of CDPKs are proposed in perpetuating stress and development triggered Ca2+ signaling to adaptive responses in plants. Genetic engineering using CDPK genes could be utilitarian in the agricultural biotechnology for imparting higher degree of biotic and abiotic stress tolerance and better productivity. Here, we discuss the recent advancements and update of CDPK gene family organization, domain structure and regulatory mechanism, the role of CDPKs in abiotic stress, biotic stress, development signaling and responses in the model and crop plants.
Dark-induced hormonal regulation of plant growth and development
(Frontiers Media S.A., 2020) Deepika; Ankit; Sagar, Sushma; Singh, Amarjeet
The sessile nature of plants has made them extremely sensitive and flexible towards the constant flux of the surrounding environment, particularly light and dark. The light is perceived as a signal by specific receptors which further transduce the information through the signaling intermediates and effector proteins to modulate gene expression. Signal transduction induces changes in hormone levels that alters developmental, physiological and morphological processes. Importance of light for plants growth is well recognized, but a holistic understanding of key molecular and physiological changes governing plants development under dark is awaited. Here, we describe how darkness acts as a signal causing alteration in hormone levels and subsequent modulation of the gene regulatory network throughout plant life. The emphasis of this review is on dark mediated changes in plant hormones, regulation of signaling complex COP/DET/FUS and the transcription factors PIFs which affects developmental events such as apical hook development, elongated hypocotyls, photoperiodic flowering, shortened roots, and plastid development. Furthermore, the role of darkness in shade avoidance and senescence is discussed.
Emerging role of phospholipase C mediated lipid signaling in abiotic stress tolerance and development in plants
(Springer Nature Publishing AG, 2021) Sagar, Sushma; Singh, Amarjeet
Environmental stimuli are primarily perceived at the plasma membrane. Stimuli perception leads to membrane disintegration and generation of molecules which trigger lipid signaling. In plants, lipid signaling regulates important biological functions however, the molecular mechanism involved is unclear. Phospholipases C (PLCs) are important lipid-modifying enzymes in eukaryotes. In animals, PLCs by hydrolyzing phospholipids, such as phosphatidylinositol-4,5-bisphosphate [PI(4,5)P2] generate diacylglycerol (DAG) and inositol- 1,4,5-trisphosphate (IP3). However, in plants their phosphorylated variants i.e., phosphatidic acid (PA) and inositol hexakisphosphate (IP6) are proposed to mediate lipid signaling. Specifc substrate preferences divide PLCs into phosphatidylinositol–PLC (PI–PLC) and non-specifc PLCs (NPC). PLC activity is regulated by various cellular factors including, calcium (Ca2+) concentration, phospholipid substrate, and post-translational modifcations. Both PI–PLCs and NPCs are implicated in plants’ response to stresses and development. Emerging evidences show that PLCs regulate structural and developmental features, like stomata movement, microtubule organization, membrane remodelling and root development under abiotic stresses. Thus, crucial insights are provided into PLC mediated regulatory mechanism of abiotic stress responses in plants. In this review, we describe the structure and regulation of plant PLCs. In addition, cellular and physiological roles of PLCs in abiotic stresses, phosphorus defciency, aluminium toxicity, pollen tube growth, and root development are discussed.
Genome-wide identification, structure analysis and expression profiling of phospholipases D under hormone and abiotic stress treatment in chickpea (Cicer arietinum)
(Elsevier B.V., 2021) Sagar, Sushma; Deepika; Biswas, Dipul Kumar; Chandrasekar, Ramsankar; Singh, Amarjeet
Phospholipases D (PLDs) are phospholipid hydrolyzing enzymes and crucial components of lipid signaling in plants. PLDs are implicated in stress responses in different plants however, characterization of PLDs in chickpea is missing. Here, we identify 13 PLD genes in the chickpea genome. PLD family could be divided into α, β, δ, ε and ζ isoforms based on sequence and structure. Protein remodeling described that chickpea PLDs are composed of defined arrangements of α-helix, β-sheets and short loops. Phylogenetic analysis suggested evolutionary conservation of chickpea PLD family with dicots. In-planta subcellular localization showed the plasma membrane localization of chickpea PLDs. All PLD promoters had hormone and stress related cis-regulatory elements, which suggested overlapping function of PLDs in hormone and abiotic stress signaling. The qRT-PCR expression analysis revealed that most PLD genes are differentially expressed in multiple abiotic stresses (drought, salt and cold stress). Moreover, several PLD genes had overlapping expression in abiotic stress and ABA and JA treatment. These observations indicate the involvement of PLD gene family in cross-talk of phytohormone and abiotic stress signaling in chickpea. Thus, present study opens new avenues of utilizing PLD related information for understanding hormone-regulated abiotic stress signaling in legume crops.
Genomic and expression analysis indicate the involvement of phospholipase C family in abiotic stress signaling in chickpea (Cicer arietinum)
(Elsevier B.V., 2020) Sagar, Sushma; Biswas, Dipul Kumar; Singh, Amarjeet
Phospholipase C proteins are phospholipid hydrolysing enzymes and crucial components of abiotic stress triggered lipid signaling in plants. PLCs are implicated in plant reaction to drought, salinity, and cold stress responses, however, characterization of the PLC family in the legume crop chickpea is missing. Here, we identify and describe nine PLC encoding genes in the chickpea genome. Phylogenetic analysis showed that the chickpea PLC family has evolved through a common path in dicots. Subcellular localization of fluorescence tagged proteins confirmed cytoplasmic and plasma membrane bound forms of PLCs in chickpea. The promoters of all the PLC genes are comprised of several hormone response related, development and abiotic stress related cis-regulatory elements. Expression analysis in five developmental stages (germination, seedling, vegetative, reproductive and senescence) showed significant expression of multiple PLCs in germination, vegetative and reproductive stages, suggesting their diverse role in various developmental processes. qRT-PCR expression analysis of the entire PLC gene family under drought, salt and cold stresses revealed that most PLC genes are differentially expressed in multiple abiotic stresses. These observations indicate the involvement of PLC gene family in abiotic stress signaling and responses in important legume crop. The present study opens new avenues for utilizing PLC- related information in biotechnological programs for abiotic stress tolerance and legume crop improvement.
Phospholipase C in abiotic stress-triggered lipid signaling in plants
(CRC Press, 2020) Sagar, Sushma; Singh, Amarjeet
The plant cell membrane plays a crucial role in abiotic stress tolerance by acting as a physical barrier, separating the internal cellular milieu from the external surroundings. Upon perception of stimulus at the cell membrane an array of steps, such as generation of secondary messengers, activation of effector protein and modifcation of the cellular metabolism, takes place (Das et al., 2017). The membrane often undergoes a remodeling process in which the membrane lipid composition changes due to the action of various regulatory membrane proteins, to adapt to the changing environmental conditions. Recent advances in plant sciences have shown that lipids regulate various cellular processes, e.g. lipid remodeling, stress tolerance, hormonal response, etc. (Heilmann, tory lipids that are involved in membrane restructuring during stress in plants (Das et al., 2017). Phospholipids are crucial for structure development of the plant cell membrane and the synthesis of secondary messengers. Phospholipases are the enzymes that act on the phospholipids to generate secondary messengers in plants. Increasing research has shown that phospholipases are involved in a wide variety of processes in plants like growth, development and regulating abiotic and biotic stress tolerance (Heilmann and Heilmann., 2015, Singh et al., 2015). Among different classes of plant phospholipases (PLA, PLC and PLD), phospholipases C (PLCs) are the important enzymes which catalyze the hydrolysis of the phospholipids. On the basis of substrate specifcity and cellular functions, PLCs in plants have been categorized as phosphoinositide phospholipase C (PI-PLC) and phosphatidylcholine-PLC (PC-PLC). PI-PLC hydrolyzes the phosphoinositides, particularly PI (4,5) P2, while PC-PLC prefers phosphatidylcholine (PC) but can also hydrolyze other lipids including phosphatidylethanolamine (PE) and phosphatidylserine (PS); therefore PC-PLC is also known as non-specifc PLC (NPC) (Aloulou et al., 2018). PI-PLC hydrolyzes the glycerophosphate ester linkage on the glycerol side of phospholipid to produce diacylglycerol (DAG) and inositol 1,4,5-trisphosphate (IP3). In animals, DAG remains bound to the membrane and activates protein kinase C (PKC) while IP3 moves to the cytoplasm where it binds to the ligand gated calcium channels and releases calcium from the intracellular reserves (Vossen et al., 2010). However, plants lack IP3 receptors and PKC, and the role of secondary messengers is played by the phosphorylated products of DAG and IP3 i.e. phosphatidic acid (PA), diacylglycerol pyrophosphate (DGPP) and hexakisphosphate (IP6). In addition to PI-PLC, DAG can also be produced by the hydrolysis activity of the NPCs that hydrolyze the phosphatidylcholine and phosphatidylethanolamine. The DAG produced by NPCs also mediates lipid signaling as a secondary messenger; thus the importance of the roles of NPCs is demonstrated in plant metabolism, plant growth and development and hormone and abiotic stress signaling (Hong et al., 2016). PI-PLCs have been reported in a wide array of plant species including nine members of Arabidopsis thaliana (Zhang et al., 2012), four of Oryza sativa (rice) (Singh et al., 2013), six of Solanum lycopersicon (tomato) (Vossen et al., 2010), three of Solanum tuberosum (potato) (Kopka et al., 1998), 12 of Glycine max (soybean) (Wang et al., 2015), one of Pisum sativum (pea) (Liu et al., 2006), three of Vigna radiata (mung bean) (Kim et al., 2004), one of Avena sativa (oat) (Huang and Crain, 2009), two of lily (Pan et al., 2005) and two of Physcomitrella (Repp et al., 2004). Also, NPCs have been reported in many plants. In-depth analysis revealed that six NPCs are encoded in the Arabidopsis genome (Hong et al., 2016), nine NPCs in soybean (Huang et al., 2010), fve NPCs in rice (Singh et al., 2013) and 11 NPCs in Gossypium hirsutum (cotton) (Song et al., 2017). In this chapter, we present an overview of PLCs in plants and discuss their various important aspects, such as domain structure, regulation of activity and signaling mechanism, along with the recent updates on the role of PLCs in abiotic stress signaling and responses in plants.
The role of extracellular ATP in plant abiotic stress signaling
(CRC Press, 2020) Sagar, Sushma; Singh, Amarjeet
Adenosine 5'-triphosphate (ATP) is one of the most important molecules in living cells. ATP is majorly produced in the mitochondria by the processes of oxidative phosphorylation by the enzyme ATP synthase. It is known as the energy currency of the cell due to its ability to store energy and distribute it to various cells as and when required; thus it is crucial for diverse cellular processes. ATP is normally present inside the cell; however, in animals it was established that ATP can come out of the plasma membrane and into the extracellular spaces (Burnstock and Knight, 2004), and this ATP is referred to as extracellular ATP (eATP). In plants, the presence of ATP in extracellular space and its effect on plant processes were studied long ago (Jaffe, 1973); however, evidence for eATP acting as a signaling molecule in plants to regulate growth and development is relatively recent (Demidchik et al., 2003; Jeter et al., 2004). The identifcation of ATPs in the extracellular spaces posed the important question of what could be specifc stimulus for the release of ATPs from within the cell to intercellular spaces in plants. To answer this question different study concluded that external stimuli like wounding, pathogen attack, touch or mechanical stimulus or abiotic stresses may cause the release of cellular ATPs to the extracellular matrix (Choi et al., 2014). In animals, ATP exodus into the extracellular matrix mainly occurs through anion channels, gap junctions, ATP binding cassettes (ABC) transporters and vesicular exocytosis (Feng et al., 2015). In addition, eATP could also be produced by a plasma membrane-localized F0F1-ATP synthase complex in animal cells (Mangiullo et al., 2008). On the other hand, the eATP pool in plants is accumulated mainly by the release of intracellular ATP through ABC transporters or by exocytosis, as an ATP synthase complex is not found at the plasma membrane of plant cells (Feng et al., 2015; Kim et al., 2006). In addition, a plasma membrane-localized transporter PM-ANT1 mediates ATP release from the pollen tube during its maturation (Rieder and Neuhaus, 2011), and its variable expression levels in a wide variety of plant tissues hint towards a vital role of ATP transport into extracellular space in plants (Clark and Roux, 2011). eATP is widely accepted as a signaling molecule in animal cells as it could stimulate an increase in vital signaling components, including cytosolic free calcium (Ca2+), nitric oxide (NO) and reactive oxygen species (ROS) (Silva et al., 2006). Moreover, eATP is essential for several crucial physiological processes such as cell growth and cell death, neurotransmission, muscle contraction and immune response in animals (Khakh and Burnstock, 2009). Several recent studies have shown signifcant involvement of eATP in crucial cellular and physiological processes in plants such as root hair growth, vegetative growth, biotic and abiotic stress responses, pollen tube growth, gravitropism and cell viability (Tanaka et al., 2010, 2014; Cao et al., 2014; Chen et al., 2017; Tripathi et and Tanaka, 2018; Hou et al., 2018). The role of eATP in different processes in animal cells could be established due to knowledge of their cognitive receptors. Two types of membrane-associated purinergic receptors are known in animal cells: P2X, the ligand gated ion channels, and P2Y, G-protein coupled receptors (Khakh and Burnstock, 2009). However, the functional role of eATP as a signaling molecule in plants could be established only recently, because a membrane-associated purinoreceptor was unknown in plants until the recent identifcation of Does not Respond to Nucleotides (DORN1), a lectin receptor kinase, by Choi et al. (2014). The DORN1 gene was identifed through a large-scale mutant screening in Arabidopsis, where it was shown to mediate some eATP-related processes (Choi et al., 2014). Identifcation of this purinoreceptor in plants has led to several interesting studies which shed the light on some important physiological roles of eATP. Thus, here we elaborate, update and provide new insights in eATP signaling, regulation and functional roles in abiotic stress signaling in plants (Figure 13.1).