"Review of literatureThe tolerance is assisted by decreased transpiration due to stomatal closure (Kang et al.,2002; Xu et al., 2014). HSF (Heat shock factor) familyHeat shock proteins/ factors are the family of genes that mediate the expressionof heat shock proteins (Chang et al., 2007; Morimoto, 2002). They recognize a cis- acting palindromic sequence which consists of multiple inverted repeats of5’AGAANNTTCT3’ binding motifs, conserved in promoters of heat shock elements(HSEs) (Xiao and Lis, 1988). There are three classes of HSFs like class A, B and Cdivided based on details of their oligomerization domains (Nover et al., 2001). A largenumber HSFs have been determined from various plants; 23 HSFs were identifiedfrom the rice (Baniwal et al., 2004; Xiong et al., 2005), 34 from soybean and 18 fromtomato (Baniwal et al., 2004). In plants, the class A HSFs, HSFA1a, HSFA1b,HSFA1d, HSFA1e, and HSFA2 have been identified as positive regulators in responseto heat shock (Nishizawa-Yokoi et al., 2011). HSFs proteins are known to play adiverse role in the plant such as sensors of reactive oxygen species (Davletova et al.,2005), thermotolerance (Meiri and Breiman, 2009) and a master regulator of HSP geneexpression during seed development (Kotak et al., 2007). HSF B proteins weresuggested to be the coactivators of HsfAs (Hahn et al., 2011). HSF B1 is a class BHSF protein known to cooperate with other transcriptional activators in controllinghousekeeping gene expression during heat stress (Bharti et al., 2004).HSF are also known to involve in various abiotic stress response and tolerance.The expression of AtHsfA2 providing tolerance to salinity and osmotic stress wasreported by Ogawa et al., (2007) and transgenic Tobacco plants expressing HaHsfA9gene has shown tolerance towards dehydration (Prieto-Dapena et al., 2008).Tolerance to heat and salt was increased in transgenic Arabidopsis with increased31 Review of literatureexpression of OsHsfA2e gene (Yokotani et al., 2008). Zinc-finger familyA zinc finger is a protein motif, which coordinates with zinc ions in order tostabilize the structure of a protein. Zinc finger proteins play an important role inprotein-protein interactions, transcriptional regulation, RNA binding, and apoptosis.They are mostly plant specific with a conserved QALGGH sequence in their zincfinger domain. Zinc finger motifs are classified into different groups based on thenumber of Cys and His residues C H , C C , C HC, C C C C , and C HCC C 2 2 2 2 2 2 2 2 2 2 2 2 (Mackay and Crossley, 1998). C H type is the classic zinc finger proteins and most2 2 abundant in eukaryotes (Laity et al., 2001). The C H motif consists of about 302 2amino acids, includes two conserved Cys and His residues. They bound a single zincion in their pocket tetrahedrally, represented as CX CX3FX5LX2HX H. Each2-4 3–5 finger forms two ß-strands and one a-helix (Pabo et al., 2001). C H type zinc finger proteins known to participate in metabolic pathways,2 2 defense and biotic and abiotic stress response (Ciftci-Yilmaza and Mittlera, 2008).About 176 plant specific C2H2 type zinc finger proteins are identified fromArabidopsis thaliana through in silico analysis (Englbrecht et al., 2004).In rice26 stress responsive C H type zinc finger proteins are reported by Agarwal et al.,2 2(2007).AP2/ERF type Transcription factorsAP2/ERF like TFs is one of the largest superfamilies of TFs, containing at leastone APETALA2 (AP2) DNA binding domain (Jofuku et al., 1994). An NMR-basedstructural analysis has revealed that an AP2/ERF domain contains an N-terminal,three strand ß-sheet and a C-terminal a-helix. The ß-sheet involve in the recognitionof target sequence (Allen et al., 1998). A variety of AP2/ERF genes were successfully32 Review of literatureidentified and investigated in various plants. There are two subfamilies in AP2/ERFsuperfamily based on the number of AP2 repeats. Proteins having single AP2 repeatinclude EREBPs/ethylene response factors (ERFs), C-repeat/dehydration responseelement binding proteins (CBFs/DREBs) and Proteins containing two AP2 repeatsinclude AP2, ANT, Spikelet1 (IDS1) and glossy15 (GL15). Each subfamily is againdivided into different groups. The DREB and ERF subfamilies were both divided intosix subgroups, A-1 to A-6 and B-1 to B-6, respectively.The AP2/ERF family members are encoded by 145 loci in Arabidopsis and167 in rice (Sakuma et al., 2002). AP2/EREBP genes are known to play a variety ofroles in the plant including the regulation of developmental processes, like floral organdetermination, control of leaf epidermal cell identity, and express in response to variousenvironmental stress. Overexpression of GmERF3 a soybean AP2/ERF TFs hasincreased the tolerance to abiotic stresses such as drought and salt stress in transgenictobacco plants (Zhang et al., 2009).The first DREB encoding DRE-binding proteins were isolated from cDNAs ofArabidopsis plant by using yeast one-hybrid gene (Liu and Zhu, 1998).TheExpression of various DREB genes like DREB1A, DREB1D, DREB2A, DREB2B, andDREB1E induced by dehydration and ABA was reported by Haake, et al., (2002) andSakuma, et al., (2002). Functional studies of DREBs indicate that CBF genescoordinate both, activation or repression of stress responsive genes.NAC Transcription factorsNAC TFs are plant-specific TFs containing a conserved NAC DNA-bindingdomain and variable C-terminal region (Riechmann, et al., 2000). The NAC domainwas originally derived from No Apical Meristem (NAM) gene in petunia (Shen et al.,2009). NAC TFs contains two domains, an N-terminal NAC domain contains a nuclear33 "