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Towards Engineering Smart Transcription Factors for Enhanced Abiotic Stress

or tissue/cell-specific promoter (root-specific RCc3 promoter) (Nakashima

et al., 2007). Thus, it may be particularly important to restrict TF activity

with the judicial choice of promoters to minimize undesirable deleterious

effects in plant engineering experiment. For example, overexpression of

ZmDREB2A under either constitutive or stress-inducible promoter led to

enhanced drought tolerance in transgenic maize plants (Qin et al., 2007).

It is now easy to make judicial choice of promoters because a plethora of

different types of natural and purpose-built synthetic promoters are available

for deriving gene expression depending on the objectives of the experiments.

For example, transgenic wheat and barley plants overexpressing wheat

DREB2 and DREB3 under both constitutive and drought inducible promoter

were generated (Morran et al., 2010). The objective of the experiment was

to study promoter which may help to increase the plant survival under stress

without deleterious effect on plant growth. Gene expression driven by stress-

inducible promoter showed no undesirable effect on plant growth whereas,

constitutive expression of the gene under drought stress exhibited multiple

unwanted phenotypic effects such as delayed flowering which led to low

yield, stunted growth, and smaller spikes (Morran et al., 2010). Reichmann

et al. (2000) reported systematic analysis of Arabidopsis TFs and identified

putative candidate genes with potential active role in stress tolerance in

plants. Nelson et al. (2007) pointed out that research results from Arabidopsis

can be directly applied to crop plant improvement. Similarly, many studies

have utilized the use of transcriptional repressor/activator which have the

potential to become important genomic tools (Hiratsu et al., 2003; Fujita et

al., 2005). In conclusion, modified TF based tools can be a potential resource

in transgenic research, attributing novel traits to the transgenic plants, espe­

cially under environmental stresses.

7.3.3 CIS-TRANS ENGINEERING LEADING TO ARTIFICIAL

TRANSCRIPTION FACTOR FOR ABIOTIC STRESS TOLERANCE

Knowledge-based modifications in DNA binding domains (DBDs)

for engineering TFs to meet particular needs require the use of current

advances in molecular biology and other allied sciences. Currently, TF

engineering (Trans engineering) strategy depends on introducing specific

modifications in the TF sequence to enhance its binding interaction

with designated target sequence (Gitzinger et al., 2009; Lu et al., 2009).

The classical reprogrammable synthetic TFs depends on the creation of