Genetic manipulations of brassinosteroid-related genes improve various agronomic traits and yield in cereals enabling new biotechnological revolution: Achievements and perspectives.

Abstract

Brassinosteroids (BRs) are steroid phytohormones which regulate various developmental and physiological processes throughout plant life cycle, from seed development and germination, up to modulation of reproduction and senescence. Importantly, mutants defective in the BR biosynthesis or response show various degree of plant height reduction (dwarfism or semi-dwarfism). This agronomic trait is of particular importance considering that in contrast to tall cereal varieties, semi-dwarf cereal plants are more tolerant to lodging which occurs during unfavorable weather conditions and constitutes a serious threat to plant reproduction and yield. Moreover, it was shown that the BR deficiency or insensitivity lead to erect stature of cereal plants what enables increase in planting density and yield. The valuable combinations of these traits make the BR-related mutants exceptional alternatives in breeding programs. Noteworthy, BRs play a noticeable role in regulation of grain/kernel shape and size. Therefore, these crucial agronomic traits may be manipulated specifically in BR-dependent manner. Importantly, the semi-dwarf mutants have been successfully introduced into cereal breeding programs in the past, and new semi-dwarf mutants developed through application of gene editing approach have been recently reported as promising alternatives for development of novel, high-yielding cereal cultivars. This review presents a comprehensive description of genetic manipulations of the BR-related genes aimed at improvements of various agronomic traits in the major cereal crops - rice, wheat, maize, and barley. These improvements may be achieved through application of panicle- or grain-specific promoters, overexpression or gain-of-function approaches, gene silencing, and targeted gene editing.