"Review of literatureKarim et al., 2015).In a few WRKY proteins, the WRKY amino acid sequences foundto be replaced by WRRY, WSKY, WKRY, WVKY or WKKY (Xie et al., 2005). The two WRKY domains of group I members appear to be functionally distinct.The C-terminal WRKY domain contributes to the overall strength of DNA. The N- terminal domain might be participating in DNA binding process and increasing thespecificity of these proteins for their target sites. Alternatively, it might provide aninterface for protein–protein interactions. The structure of the C-terminal WRKY foundto form a four-stranded ß-sheet (Yamasaki et al., 2013) and the N-terminus of thedomain contains an additional ß- strand (Duan et al., 2007). The single WRKYdomains of group II and III members are more similar to the C-terminal domain ofgroup I family. This suggests that the single C-terminal WRKY domain is functionallyequivalent and contribute to DNA binding. It was proposed that the ß-strand containing the WRKYGQK motif makescontact with an approximately 6-bp cis-acting element W Box. The conservation of theWRKY domain is mirrored by a remarkable conservation of its cognate binding site,the W box (TTGACC/T) sequence (Rhuston et al., 1996; Eulgem et al., 2000; Agarwalet al., 2011; Brand et al., 2013). The interaction takes place as the four-stranded ß-sheetenters the major groove of DNA which lies perpendicular to the DNA helical to form ß- wedge. WRKYGQK signature motif contacts the W Box DNA bases mainly throughextensive polar contacts with thymine methyl groups (Yamasaki et al., 2012). WRKY protein and DNA W box interactions have been demonstrated bynumerous binding experiments, both in vitro and in vivo (Eulgem et al., 1999:Yamasaki et al., 2012). A detailed study on the binding selectivity of five WRKYproteins was performed in Arabidopsis using gel shift experiments. The resultssuggested that the W box is required for binding of WRKY proteins, but adjacent37 Review of literaturesequences also play a role in determining the binding site (Ciolkowski et al., 2008).WRKY TFs are known involve in growth, developmental and stress response in plants(Ramamoorthy et al., 2008; Wei et al., 2012b; Saenz-Mata and Jimenez-Bremont, 2012). A large number of WRKY TFs have been identified and characterized fromvarious plant species (Liu et al., 2014b; Cai et al., 2015; Sun et al., 2015).Roles played by WRKY transcription factorsWRKY TFs play an important role in biotic stresses, such as bacterial, fungal,and viral pathogens (Pandey and Somssich, 2009; Jiang et al., 2014).WRKY proteinsare also involved in plant processes, like seed development (Craig and Ling 2014),embryogenesis (Ueda et al., 2011), dormancy (Ding et al., 2014; Craig and Ling 2014), trichome development (Bakshi and Oelmüller, 2014), senescence (Besseau et al., 2012;Rinerson et al., 2015b), signal transduction ( Rinerson et al., 2015a) fruit developmentand ripening (Klee and Giovannoni, 2011) and various abiotic stresses (Ren et al.,2010;Okay et al., 2014; Niu et al., 2012). DevelopmentWRKYs have been implicated to be regulating the plant growth anddevelopment (Rushton et al., 2010; Mao et al., 2011; Grunewald et al., 2013). WRKYTFs regulates the plant growth, such as seed germination, development, seed dormancy,root formation, morphogenesis of trichomes, and metabolic pathways. SolanumLycopersicum WRKY TFs like SlWRKY8, SlWRKY10 and SlWRKY78 appeared to beexpressed in hypocotyls, cotyledon, fruit exocarp and root (Huang et al., 2012).InArabidopsis, WRKY23 TF gene favoured root growth development by facilitating theauxin distribution in the plant (Grunewald et al., 2012).38 Review of literatureSeed dormancy and germinationA number of studies have suggested that WRKY genes mediate seedgermination and growth in plants. Two WRKY family proteins ABF1 and ABF2 werederived from the wild oat.They found to bind the conserved cis-element in thepromoters of a-amylase gene a-Amy2 (Rushton et al., 1995) involving in thehydrolysis of starch, thereby promoting the seed germination by breaking dormancy.WRKY2 TF gene from Arabidopsis promotes seed germination and growth throughABA-dependent signal pathway (Jiang and Yu, 2009). ABO3 an ABA-upregulatedWRKY gene involved in seed germination and root growth (Ren et al., 2010).WRKY41 gene was identified from the Arabidopsis plant controlling the ABI3transcript pathway and thereby seed dormancy (Ding et al., 2014).SenescenceWRKY TFs also involves in plant process such as the regulation of leafsenescence. They can regulate the senescence in both positively and negatively.Senescence is a normal cellular process under the control of nucleus. Several WRKYTF genes are known to be expressed during leaf senescence (Besseau and Palva, 2012).Guo et al., (2004) has proposed that the WRKY TFs are the second largest family ofTFs involving in the senescence of leaves. The first evidence for the involvement of WRKY in senescence was reported inArabidopsis thaliana. AtWRKY6 TFs strongly upregulated at the time of senescencewas isolated from Arabidopsis by Robatzek and Somssich (2001). Expression ofOsWRKY42 in rice has repressed the OsMT1d gene expression and favored theinduction of ROS and Senescence (Han et al., 2014) .Overexpression of OsWRKY23 TFfrom rice enhancing leaf senescence was reported by Jing et al., (2009). The repressionof WRKY53 TF gene has delayed the leaf senescence in Arabidopsis during the39 "