205

Towards Engineering Smart Transcription Factors for Enhanced Abiotic Stress

(cold, salinity, and drought) in transgenic rice (Nakashima et al., 2007; Hu

et al., 2008; Zheng et al., 2009). Studies have shown that Overexpression

of three DREB1s/CBFs (DREB1A/CBF3, DREB1B/CBF1, and DREB1C/

CBF2) significantly could improve tolerance to freezing, drought, and high

salinity in transgenic Arabidopsis (Gilmour et al., 2004; Novillo et al., 2004).

Overexpression of MYB15 in Arabidopsis plants improved salt and drought

tolerance of transgenic plants by high expression of various stress-related

proteins and stomatal closure under water shortage (Ding et al., 2009). High

cuticular wax accumulation and enhanced drought tolerance was observed

in transgenic plants overexpressing WXP1 and SHINE1-3 TFs which show

that these TFs are involved in induction of wax related genes (Zhang et

al., 2005, 2007). Yang et al. (2012a) reported that transgenic plants over-

expressing OsMYB2 TF exhibited enhanced tolerance to various stresses

(Drought, Salt, freezing) by altering expression levels of many downstream

stress-responsive genes. Overexpression of two transcription factors from

soybean, GmMYB76 or GmMYB177 in Arabidopsis led to salt and freezing

tolerance (Liao et al., 2008). Qiu & Yu (2009) reported the Overexpres­

sion of OsWRKY45 in Arabidopsis conferred drought tolerance mainly

due to stomatal closure and induction of downstream stress-related genes

under drought stress. Similarly, rice and Arabidopsis plants overexpressing

OsWRKY11 and VvWRKY exhibited significantly high heat, drought, and

osmotic stress tolerance (Wu et al., 2009). Similarly, Arabidopsis transgenic

plants overexpressing two soybean GmWRKY21, GmWRKY54 genes

showed improved tolerance to cold, drought, and salt stresses (Zhou et al.,

2008). In another attempt, Xiang et al. (2008) studied the overexpression of

OsbZIP23 in rice. Expression analysis of transgenic plants showed changes

in the expression of over 1,000 genes and many of these have significant

roles in drought and salinity tolerance (Xiang et al., 2008). As a matter of

fact, the above discussion highlighted the significant roles of transcription

factors in gene regulation under different stresses which make these genes

ideal candidates for engineering multiple abiotic stress tolerance in crop

plants (Hussain et al., 2011a).

7.3.2 STRATEGIES FOR MANIPULATING TRANSCRIPTION FACTOR

ACTIVITY IN TRANSGENIC PLANTS

Constitutive overexpression of key regulatory proteins like TFs might

show some undesirable negative effects such as stunted growth, unwanted