"Review of literatureMYB transcription factor family MYB TFs represent a family of proteins that include the conserved MYB DNA- binding domain. The first MYB gene identified was the v-MYB gene of avianmyeloblastosis virus (AMV) (Klempnauer et al., 1982). They are widely distributed inplants and have been implicated in the ABA response and interact with other TFs. TheMYB-motif comprises three imperfect repeats each with about 52 amino acid residuesthat and confers a helix-turn-helix secondary structure with a functional MYB-domain,intercalating in the major groove of the DNA (Yanhui et al., 2006). There are threesubfamilies in MYB (1) R2R3, having two adjacent repeats and is the largestsubfamily in MYB genes family (2) R1R2R3, have three adjacent repeats and (3)MYB-related TFs containing a single MYB repeat (Hou et al., 2014).The MYB genefamily is represented by 190 genes in Arabidopsis (Riechmann et al., 2000). Katiyar etal., (2012) have reported 197 MYB TFs in Arabidopsis and 155 individuals in the ricegenome.MYB TFs play important roles in many physiological processes under normaland unfavorable growth conditions (Shim and Choi, 2013). They also known to involvein cell signalling (Shim et al., 2013) , cell cycle control (Araki et al., 2004), cellmorphogenesis (Higginson et al., 2003), stress response and defence (Cao et al., 2013),and in hormone signalling (Qi et al., 2014) and fruit development (Cao et al., 2016).Expression of MYB in plant stress response and the defense was widely reported inmany studies (Gao et al., 2011; Hrmova and Lopato, 2014). AtMYB60 and AtMYB61,R2R3-MYB genes of Arabidopsis, were specifically expressed in guard cells andregulate stomatal movement (Gray, 2005). AtMYB60 and AtMYB61 are involved inlight-induced opening and dark-induced closing of stomata (Cominelli et al., 2005;Liang et al., 2005). Overexpression AtMYB44 TF gene from Arabidopsis has enhanced28 Review of literatureabiotic stress tolerance in transgenic conferring by favoring the stomatal closureunder stress conditions (Jung et al., 2008).The expression of CpMYB10 in transgenic Arabidopsis plants resulted indrought and salinity tolerance (Villalobos et al., 2004). MYB TFs are known to involvein cuticular wax biosynthesis. Transcriptional activation of Arabidopsis MYB96 hasimproved cuticular wax biosynthesis in turn increasing drought tolerance was reportedby Seo et al., (2011). Plants Overexpressing MYB genes like MYB15, StMYB1R-1,OsMYB4, resulted in improved drought was also reported previously (Shin et al.2011; Vannini et al., 2007). bZIP Transcription factors Leucine zipper (bZIP) TFs has a basic region that binds to DNA and a leucinezipper dimerization motif. It is one of the largest and most diverse TF families. ThebZIP domain is 60 to 80 amino acids in length. The basic region consists of about16 amino acid residues characterized by the presence of an invariant N-x7-R/K motif;whereas the Leucine zipper is composed of heptad repeats of Leucine or otherhydrophobic amino acids like Isoleucine, Valine, Phenylalanine and methionine (Wei etal., 2012a; Liu et al., 2015a). Leucine zipper of bZIP proteins mediateshomodimerization or heterodimerization of monomers through a parallel interactionwith hydrophobic dimerization of two a-helices, resulting in a coiled-coil structure(Jacoby et al., 2002; Wei et al., 2012). bZIP TFs regulate diverse biological processessuch as pathogen defence (Kaminaka, et al., 2006), stress signalling, seed maturation,flower development organ and tissue differentiation (Silveira et al., 2007) and bioticand abiotic stress response (Liu et al., 2015a; Nakashima et al., 2014). They express indifferent ways such as organ-specific, stimulus responsive and development-dependentand cell cycle specific (Nijhawan et al., 2008; Rodriguez- Uribe and O’Connell, 2006).29 Review of literatureHu et al., (2016) have identified 121 putative genes encoding proteins with the bZIPsignature from banana under drought stress and 89 bZIPs were identified from rice byNijhawan et al., ( 2008). The plant hormone ABA plays an important role in the adaptive response of theplant to drought, cold and high-salinity. A number of bZIP TFs are known to participatein ABA-mediated signaling (Fujita et al., 2005; Nakashima et al., 2014). The bZIP TFsinteract with a specific ABA-responsive element containing ACGTGGC promoterregion thereby transactivating downstream gene expression ( Xu et al., 2014).Table 2: Validated bZIP genes for drought stress from rice and Arabidopsis.Gene name Transgenics Tolerant phenotype ReferencesABF3 Arabidopsis Drought Kang et al., 2002ABF4 Arabidopsis Drought Kang et al., 2002ABP9 Arabidopsis Drought Zhang et al., 2008OsbZIP23 Rice Drought, Salinity Xiang et al., 2008OsbZIP72 Rice Drought Lu et al., 2009OsAREB1 Rice Drought, Heat Jin et al., 2010ZmbZIP72 Arabidopsis Drought, Salinity Ying et al., 2012OsbZIP46 Rice Drought Tang et al., 2012,OsbZIP16 Rice Drought Chen et al., 2012aSeveral ABA-responsive bZIP TFs that induce gene expression by abiotic stressare identified and cloned. Zhang, et al., (2015) has reported the multiple abiotic stressesin transgenic Arabidopsis plants expressing TabZIP60 gene from wheat. Theoverexpression of OsbZIP23 and OsbZIP72, genes has enhanced the abiotic stresstolerance in rice by regulating the ABA signaling (Lu et al., 2008; Xiang, et al., 2008).Expression of ThbZIP1 gene from Tamarix hispida has increased the abiotic stresssignaling in transgenic Arabidopsis plants (Ji et al., 2013). Enhanced drought tolerancewas recorded in transgenic Arabidopsis plants overexpressing ABF3 and ABF4 genes.30 "