The most consistent phenotype of the brassinosteroid (BR)-related mutants is the dwarf habit. This observation has been reported in every species in which BR action has been studied through a mutational approach. On this basis, a significant role has been attributed to BRs in promoting plant growth. In this review, we summarize the work conducted in rice, maize, and barley for the genetic dissection of the pathway and the functional analysis of the genes involved. Similarities and differences detected in these species for the BR role in plant development are presented. BR promotes plant cell elongation through a complex signalling cascade that modulates the activities of growth-related genes and through the interaction with gibberellins (GAs), another class of important growth-promoting hormones. Evidence of BR-GA cross-talk in controlling plant height has been collected, and mechanisms of interaction have been studied in detail in Arabidopsis thaliana and in rice (Oryza sativa). The complex picture emerging from the studies has highlighted points of interaction involving both metabolic and signalling pathways. Variations in plant stature influence plant performance in terms of stability and yield. The comprehension of BR's functional mechanisms will therefore be fundamental for future applications in plant-breeding programs.
Keywords: Hordeum vulgare; Oryza sativa; Zea mays; brassinosteroids; cell elongation; gibberellins; plant development; plant mutants; plant stature; transcriptional regulation.