"Review of literaturegenome. A SnRK2 kinase gene involving in somatic stress tolerance through anabscisic acid depended on signaling pathway in Arabidopsis was reported by Yoshidaet al., (2015). Overexpression of wheat TaSnRK2 has improved the plant tolerancetowards abiotic stresses such as drought, salt and the low temperature was reported intransgenic Arabidopsis plants (Zhang et al., 2010). Manipulation of SnRK familyprotein has found to increase stress tolerance and favoures yield production in plants(Coello et al., 2011).Calcium signalingCalcium ions play an important role in cell signaling. It acts as the second2+ messenger in signal transduction pathways. In general, cell keeps low Ca levels2+ operating between 100 – 200 nM in the resting. Increases in Ca level more than200mM can serve as a second messenger. In plant cells, during abiotic stress signaling2+ it can bring about a cellular response to increasing calcium concentration (Ca ) whichserves as a second messenger (Kudla et al., 2010; Bickerton and Pittman, 2012). The2+ Ca signature changes depending on the type of stress, type of tissue, previousexposure to stress and rate of stress development (Plieth et al., 1999).2+ Three major classes of Ca sensors are identified from plants involving instress signal transduction (Gao et al., 2013). They are calmodulin, calcium-dependentprotein kinase (CDPKs) and calcineur in B-like proteins (CBLs) (Yang and Poovaiah,2003; Bartels and Sunkar, 2005). Involvement of calcium in plant signalling, plantgrowth and stress response has been reported from several plants (Reddy et al., 2011;Dubiella et al., 2013; Zhou et al., 2014) Involvement of a calcium-dependent proteinkinase SDPK8 in abscisic acid-mediated signalling under drought stress conditions wasreported in Arabidopsis plant (Zou et al., 2015).25 Review of literature In some cases, the overexpression of AtCaMBP25 led to sensitivity to osmoticor salt stresses in Arabidopsis, whereas the suppression of this gene by antisensetechnology has resulted in improved tolerance (Perruc et al., 2004). The aboveinformation provides convincing evidence for achieving the desired level of stresstolerance by manipulating signaling cascade molecules. Phospholipid signallingPhospholipids are membrane components that form lipid bilayer because of theamphiphilic nature. The plasma membrane plays an important role in perceiving andtransmitting environmental signals. In general,lipid signaling pathway is activated byreceptor trigger, phospholipase C (PLC) which hydrolyzes phosphatidylinositol 4,5- bisphosphate (PI-4,5-P2) to produce inositol 1,4,5-trisphosphate (IP3) anddiacylglycerol molecules that play a major role in signaling (Meijer andMunnik, 2003). Phospholipases are the enzymes that cleave phospholipids and producephospholipid-derived second messengers. Phospholipases are four types based on theircleavage site, phospholipase C (PLC), phospholipase D (PLD) and phospholipase Aland A2 (PLA1 and PLA2) (Wang, 2002).Osmotic stress signals in plants are recognized by the altered membrane fluidityand change in phospholipids (Munnik and Meijer, 2001). The major phospholipidsderived signaling molecules involved in osmotic stress are in inositol-1,4,5-triphosphate(IP3), diacylglycerol (DAG) and phosphatidic acid (PA). Elevated activity of PLD wasfound in a drought sensitive cowpea when compared to tolerant strain (El-Maarouf etal., 1999). Phospholipase C also is known to involves in ABA-mediated stomatalclosure in response to water stress (Jacob et al., 1999). 26 Review of literatureRole of TFs in abiotic stress responsesTranscription factors (TFs) are proteins that initiate and regulate thetranscription of genes. They act alone or together with other transcriptional regulatorsto engage or clog RNA polymerases to the DNA template (Udvardi et al., 2007).TheTFs contain a DNA binding domain that specifically recognizes the target DNAsequence to form a transcriptional complex and thus regulate gene expression (Rinersonet al., 2015a; Gujjar et al., 2014). A large number of TFs and several protein complexesassist the polymerization. A typical plant TF consists of a DNA-binding region, atranscription regulation domain, and a nuclear localization signal. TFs binds tospecific DNA sequence thereby it controls the rate of transcription. Under stressconditions the TFs interact with cis-elements in the promoter region of the gene andup-regulate the expression of many downstream genes resulting in imparting abioticstress tolerance (Agarwal et al., 2011; Li et al., 2013). Hence the engineering of TFsgenes provides a valuable means for manipulation of plants for stress tolerance(Tripathi et al., 2014; Dai et al., 2015).Transcriptional regulation in plants is a complex process (Bakshi and Oelmuller,2014). Plant genome appears to encode more TFs than animals. More than 1500 TFsinvolved in stress-responsive gene expression are described from Arabidopsis thalianagenome by Riechmann et al., (2000) and others (Guo and Gan, 2006). With theavailable EST sequences, a large number of TFs were identified from different plantspecies (Guo et al., 2008; Xin et al., 2013). Usually, TFs are classified on their DNAbinding domains. Most of the stress-responsive TFs belong to the families of MYB,bZIP, HSF, AP2/ERF, NAC, MYC, HD-ZIP, Zinc-finger and WRKY (Nakashima andYamaguchi- Shinozaki, 2005; Gujjar et al., 2014).27 "