Overexpression of a brassinosteroid biosynthetic gene Dwarf enhances photosynthetic capacity through activation of Calvin cycle enzymes in tomato

Background: Genetic manipulation of brassinosteroid (BR) biosynthesis or signaling is a promising strategy to improve 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 by overexpressing Dwarf, a BR biosynthetic gene that encodes the CYP85A1, and compared the photosynthetic capacity with the BR biosynthetic mutant d(im) and wild type. Results: Overexpression of Dwarf promoted net photosynthetic rate (P-N), whereas BR deficiency in d(im) led to a significant inhibition in P-N as compared with WT. The activation status of RuBisCO, and the protein content and activity of RuBisCO activase, but not the total content and transcripts of RuBisCO were closely related to the endogenous BR levels in different genotypes. However, endogenous BR positively regulated the expression and activity of fructose-1,6-bisphosphatase. Dwarf overexpression enhanced the activity of dehydroascorbate reductase and glutathione reductase, leading to a reduced redox status, whereas BR deficiency had the contrasting effects. In addition, BR induced a reduction of 2-cystein peroxiredoxin without altering the protein content. Conclusions: BR plays a role in the regulation of photosynthesis. BR can increase the photosynthetic capacity by inducing a reduced redox status that maintains the activation states of Calvin cycle enzymes.