The Role Of Overex Pressing Brassinosteroid Biosynthetic Gene DWARF In Tomato

Genetic manipulation of brassinosteroid (BR) biosynthesis or signaling is a promising strategy to improve the crop yield and quality. However, the relationships between the BR-promoted growth and photosynthesis, and the exact mechanism of BR-regulated photosynthetic capacity are not clear. Here, we generated transgenic tomato plants overexpressing the BR biosynthetic gene, DWARF, encoding the CYP85A1, and compared the photosynthetic capacity with the BR biosynthetic mutant dim and wild type.Overexpression of DWARF promoted net photosynthetic rate (PN), whereas BR deficiency in dim led to a significant inhibition of PN, with concomitant decline of stomatal conductance, as compared with WT. Regulation of PN by BR levels in transgenic or mutant plants was closely related to the activation status of RuBisCO and the activity of RuBisCO activase, but not the total content and transcripts of RuBisCO. Meanwhile, the activity and expression of FBPase were positively regulated by BR. DWARF overexpressing plants exhibited enhanced activity of dehydroascorbate reductase, and glutathione reductase, leading to a reduced redox status, whereas BR deficiency had contrasting effects on the antioxidant capacity and redox status. In addition, BR induced a reduction of 2-cysteinperoxiredoxin, but not the protein content. The results provide genetic evidence that BR is essential for the photosynthesis and suggest that BR increases the photosynthetic capacity by inducing a reduced redox status, which maintains Calvin cycle enzymes in the active states.Brassinosteroids (BRs) play a critical role in plant growth, development and stress response; however, genetic evidence for the BRs-mediated integrated regulationof 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, dim, 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 downregulated 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 meter in two transgenic lines due to their compact architecture. Significantly, BRs 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.