The bZIP TFs represents one of the largest andmost diverse family in eukaryotes and are known to affect almost all phases ofthe plant life cycle. They have been shown to regulate number of plantprocesses such as seed germination, seed maturation, photomorphogenesis, floralinduction and flower development , biotic and abiotic stresses, ABA signallingand hormonal response (Bensmihen et al. 2005, Jakoby et al. 2002; Nijhawanet al.
2008). The bZIP TFs derivetheir name from a bZIP domain that is highly conserved and is made up of abasic region with a leucine zipper domain (Hurst 1995). The current number of bZIP gene models in ricegenome has been predicted to be 140 and 94 for japonica and indicarespectively (Jin et al. 2017). Earlier, a detailed analysis of this family identified 89 bZIP proteinencoding genes in rice (Nijhawan et al. 2008).
Functional analysis of bZIP genes in rice haveshown their ability to regulate abiotic stress signalling and responses in Arabidopsis as well as in rice. In rice,OsbZIP23 is rapidly and strongly inducedby drought, ABA, PEG and NaCl treatment and also confers tolerance to abiotic stress by regulating stressrelated gene expression in an ABA-dependent manner (Xiang et al. 2008). Similarly, OsbZIP46is up-regulated to high levels under drought, heat and ABA treatment (Tang et al. 2012).
The over-expression of OsbZIP46 increased sensitivity to ABA. However, its over-expressiondid not promote drought tolerance. Another ABA induced bZIP TF, OsBZ8 expressed strongly insalt-tolerant rice varieties compared to their salt-sensitive counterparts (Nakagawa et al. 1996; Mukherjee et al. 2006).
Among the core regulators of ABA sensitivity, OsABI5, a bZIP family member encodes forABRE/G-box binding protein (Zou et al. 2007; Zou et al. 2008). OsABI5protein localizes to nucleus, has trans-activity but negatively regulatesstress tolerance on over-expression in rice.
Similarly, OsbZIP16 in rice promotes ABA sensitivity but promotes droughtresistance in rice (Chen et al. 2012). OsbZIP52 is induced by low temperature(4°C) and its over-expression increases susceptibility to cold and droughtstress in rice (Liu et al. 2012).