Abstract
Brassinosteroids (BRs) play a critical role in plant growth, development and stress response; however, genetic evidence for the BR-mediated integrated regulation of plant growth still remains elusive in crop species. Here, we clarified the function of DWARF (DWF), the key BR biosynthetic gene in tomato, in the regulation of plant growth and architecture, phytohormone homeostasis and fruit development by comparing wild type, d^(im), a weak allele mutant impaired in DWF, and DWF-overexpressing plants in tomato. Results showed that increases in DWF transcripts and endogenous BR level resulted in improved germination, lateral root development, CO2 assimilation and eventually plant growth as characterized by slender and compact plant architecture. However, an increase in DWF transcript down-regulated the accumulation of gibberellin, which was associated with decreases in leaf size and thickness. BRs positively regulated lateral bud outgrowth, which was associated with decreased transcript of Aux/IAA3, and the ethylene-dependent petiole bending and fruit ripening. Notably, overexpression of DWF did not significantly alter fruit yield per plant; however, increases by 57.4% and 95.3% might be estimated in fruit yield per square metre in two transgenic lines due to their compact architecture. Significantly, BR level was positively related with the carotenoid accumulation in the fruits. Taken together, our results demonstrate that BRs are actively involved in the regulation of multiple developmental processes relating to agronomical important traits.