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bZIP TFs represents a large and diverse multigene family in eukaryotes and are
known to affect almost all phases of the plant life cycle. They have been shown
to regulate number of plant processes such as seed germination, seed maturation,
photomorphogenesis, floral induction and flower development , biotic and
abiotic stresses, ABA signalling and hormonal response (Bensmihen et al. 2005, Jakoby et al. 2002; Nijhawan
et al. 2008). The bZIP TFs derive their name
from a bZIP domain that is highly conserved and is made up of a basic region
with a leucine zipper domain (Hurst 1995). The current number
of bZIP gene models in rice genome has been predicted to be 140 and 94 for japonica and indica respectively (Jin et al. 2017). Earlier, a detailed
analysis of  this family identified 89 bZIP
protein encoding genes in rice (Nijhawan et al. 2008). Functional
analysis of bZIP genes in rice have shown their ability to regulate abiotic
stress signalling and responses in Arabidopsis
as well as in rice. In rice, OsbZIP23 is
rapidly and strongly induced by drought, ABA, PEG and NaCl treatment  and also confers tolerance to abiotic stress
by regulating stress related gene expression in an ABA-dependent manner (Xiang et al. 2008). Similarly, OsbZIP46 is 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-expression did not promote drought tolerance. Another
ABA induced bZIP TF, OsBZ8 expressed
strongly in salt-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 for ABRE/G-box binding protein (Zou et al. 2007; Zou et al. 2008). OsABI5 protein localizes to nucleus,
has trans-activity but negatively regulates stress tolerance on over-expression
in rice. Similarly, OsbZIP16 in rice promotes
ABA sensitivity but promotes drought resistance in rice (Chen et al. 2012).  OsbZIP52
is induced by low temperature (4°C) and its over-expression increases
susceptibility to cold and drought stress in rice (Liu et al. 2012).

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