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Biology and Biotechnology of Environmental Stress Tolerance in Plants, Volume 3

responses to various abiotic stresses (Shinozaki et al., 2003; Yamaguchi-

Shinozaki & Shinozaki, 2005). Similarly, high throughput genomic tech­

niques in combination with bioinformatics analyzes have greatly facilitated

gene function and cloning (Seki et al., 2001, 2007; Abe et al., 2003; Tran et

al., 2004). These developments enabled manipulation of functional or regu­

latory genes for stress tolerance to various abiotic stresses in plants (Trujillo

et al., 2009).

Transgenic approaches in developing tolerant plants to different abiotic

stress have been significantly enhanced by one or multigene transfer to the

target plant. Overexpression of target genes in model and crop plants allowed

researchers to explore and validate the molecular mechanism of stress toler­

ance and their protective effects against various environmental stresses. After

detailed research, it is concluded that two gene categories exist. Regulatory

genes are either involved in signaling and/or regulatory pathways other

genes encode enzymes resulting in the synthesis of functional and structural

protectants (Bartels & Hussain, 2008; Hu et al., 2010; Hussain et al., 2012).

Another development is that state of the art technologies allow to charac­

terize many genes simultaneously to explore their structure, function, and

interaction under stress. Though labor intensive, generating transgenic plants

seems a tricky but suitable option for generating tolerant plants, given the

multigenic nature of abiotic stress tolerance, potential negative effects on

plant growth and other scientific limitations.

Metabolic engineering for higher compatible solutes/osmolyte (referred

to as osmoprotectants) has shown remarkable success in different plants

under various stresses (Garg et al., 2002; Wang et al., 2003; Park et al.,

2007). However, Serraj & Sinclair (2002) raised questions on the real advan­

tages of such plant engineering strategy. Several studies have successfully

engineered crop plants and discussed the functions of the osmolytes in plants

under stress (Hasegawa et al., 2000; Garg et al., 2002; Chaves & Oliveira,

2004; Vinocur & Altman, 2005; Valliyodan & Nguyen, 2006; Kumar et al.,

2006; Molinari et al., 2007; Gubis et al., 2007; Park et al., 2007; Vendrus­

colo et al., 2007; Ahmad et al., 2008; Chen et al., 2009; Suarez et al., 2009;

Alcazar et al., 2010; Thippeswamy et al., 2010). Plants use these osmolytes

for maintaining turgor pressure, decreasing the osmotic potential in the

cytoplasm, protects different cellular compartments from injury, and help

to stabilize the structure and function of macromolecules (sensitive proteins

and the vital membranes) under different environmental constraints (McNeil

et al., 1999; Hasegawa et al., 2000; Park et al., 2007; Hussain et al., 2012).

Several compatible solutes such as Glycine betaine (Naidu et al., 1991;