Glycine betaine: Role in shifting plants toward adaptation under extreme environments

World is facing serious threat in terms of global food requirement for the eradication of hunger. The latest FAO estimates clearly indicate that about 805 million people are still chronically undernourished in the year 2012-2014, and the area under cultivation is diminishing because of various anthropogenic activities including contamination of soil by heavy metal, industrial salts, etc. Therefore, it becomes the need of the hour that certain crops will be designed that have the ability to withstand such harsh environments and help in sustainable crop development. The research in this area has already gone a step ahead, and scientist has developed crops through genetic engineering that due to certain induced traits can tolerate extreme environments. Recent advances in production of transgenic plants with higher rate of GB accumulation help them in their survival against abiotic stresses and are the promising tool for sustainable agriculture. Transgenic Arabidopsis, cotton, etc. have already been reported to accumulate higher levels of betaine and provide tolerance against abiotic stresses. Further, recent developments indicate that phytohormones play prominent role in the regulation of S-assimilation and also are crucial signaling molecules involved in the control of plant responses under optimal and limited environmental conditions. However, in this chapter, we try to detail out the mechanism on which GB works to protect photosynthesis and growth and its interactive effect with nutrients and phytohormones.