Stress-Inducible Galactinol Synthase of Chickpea (CaGolS) is Implicated in Heat and Oxidative Stress Tolerance Through Reducing Stress-Induced Excessive Reactive Oxygen Species Accumulation

Raffinose family oligosaccharides (RFOs) participate in various aspects of plant physiology, and galactinol synthase (GolS; EC 2.4.1.123) catalyzes the key step of RFO biosynthesis. Stress-induced accumulation of RFOs, in particular galactinol and raffinose, has been reported in a few plants; however, their precise role and mechanistic insight in stress adaptation remain elusive. In the present study, we have shown that the GolS activity as well as galactinol and raffinose content are significantly increased in response to various abiotic stresses in chickpea. Transcriptional analysis indicated that the CaGolS1 and CaGolS2 genes are induced in response to different abiotic stresses. Interestingly, heat and oxidative stress preferentially induce CaGolS1 over CaGolS2. In silco analysis revealed several common yet distinct cis-acting regulatory elements in their 5'-upstream regulatory sequences. Further, in vitro biochemical analysis revealed that the CaGolS1 enzyme functions better in stressful conditions than the CaGolS2 enzyme. Finally, Arabidopsis transgenic plants constitutively overexpressing CaGolS1 or CaGolS2 exhibit not only significantly increased galactinol but also raffinose content, and display better growth responses than wild-type or vector control plants when exposed to heat and oxidative stress. Further, improved tolerance of transgenic lines is associated with reduced accumulation of reactive oxygen species (ROS) and consequent lipid peroxidation as compared with control plants. Collectively, our data imply that GolS enzyme activity and consequent galactinol and raffinose content are significantly increased in response to stresses to mitigate stress-induced growth inhibition by restricting excessive ROS accumulation and consequent lipid peroxidation in plants.