179

Plant Breeding Approaches in Developing Stress Tolerance

Transgenic plants with HSPs are tolerant to heat stress by minimizing

the protein denaturation with the help of protein homeostasis (Jacob et al.,

2017). Many studies showed that the expression of the HSPs in Arabidopsis

plant and tomato plant has made it resistant to high-temperature stress. In

Glycine max, the expression of the heat shock factor made it tolerant through

the stimulation of the many downstream genes’ expression involved in heat

defense system (Zhang et al., 2015a, b, c). Likewise, the introduction of

VpHSF1 gene in tobacco plants increased the capacity to tolerate high-

temperature stress as compared to nontransgenic tobacco plants (Hu et al.,

2016). The points mentioned above showed that the heat shock factor genes

are the best player to confer heat stress. Therefore, abiotic stress tolerance

can be induced efficiently by transgenic approaches.

6.5.3.2.3 TRANSGENIC APPROACHES FOR SALT STRESS TOLERANCE

Salt accumulation in agricultural land is serious issue crop plants face

regarding disturbed physiology and retarded growth. Salt accumulation is

very severe abiotic stress affecting crop yield globally (Bless et al., 2018).

Recently reported that approx. 77 million hectare of agricultural land is not

suitable for cultivation due to excessive salt accumulation (Bless et al., 2018).

Generally, the soil with more than 4 dS m^–1 electrical conductivity (EC)

and 40 mM sodium chloride with 15% exchangeable sodium rate is called

saline soil (Singh, 2015). The main agents involved in soil salinization are low

precipitation, saline water irrigation, poor agronomic practices, and weathering

of rocks. If not checked, more than 50% of agricultural land will be saline land

up to 2050 (Singh, 2018). As other abiotic stresses have a very complicated

regulatory setup, saline stress is complex in regulation and is controlled by

many genes (Munns & Gilliham, 2015). Some studies showed that plants

tolerant to abiotic stress could also manufacture many pathogenic proteins to

mitigate the effect of stress (Negrao et al., 2017). Many pathogenesis-related

proteins among these Osmotin proteins can generate innate immunity in plants

against abiotic stresses (Wan et al., 2017). Osmotic genes taken from tobacco

plants are introduced in strawberry plants showed tolerance against salt stress

(Sripriya et al., 2017). Transgenic chili with the Osmotin genes is tolerant

to salt stress up to 300 mM NaCl, leading to increased antioxidant enzymes

activities and photosynthesis rate (Ullah et al., 2018).

Transgenic cherry tomato having D-galacturonic acid reductase

gene could bear salt stress up to 200 mM and improve the stress defense