Brassinosteroids: Biosynthesis and Role in Growth, Development, and Thermotolerance Responses

Abstract

Brassinosteroids are new and unique class of plant growth regulators that constitutes the sixth class of phytohormones. Till date more than 70 analogues of these natural occurring and nonnatural analogues of brassinolides (BL) have been identified from different plant species. Brassinoslides due to their ubiquitous presence in plant species in almost all parts of plant orchestrate myriad growth and developmental processes. Owing to their peculiar structural features, their extremely low abundance in natural sources, and potent biological activity, BLs are being studied intensively to understand their role in plant metabolism under normal and inadequate growth conditions. Their main physiological effects in plants include cell division control, germination and growth promotion, regulation of hormonal balance, activation of protein and nucleic acid synthesis, enzyme activity, and most interestingly increased resistance to abiotic and biotic stresses. Exogenous application of BLs to plants at seed level or as foliar spray enhances antioxidant defense activities, and accumulation of osmoprotectants such as proline and glycine betaine under stress conditions illustrated antistress properties of brassinosteroids. BLs reported to play a regulatory role in the control of cell-cycle progression and differentiation in the Arabidopsis, and other plants may offer a novel therapeutic strategy for various diseases.