Brassinosteroids regulate amylose more sensitively than amylopectin: Essential for high-amylose premium rice

Brassinosteroids (BRs) are crucial for plant growth, but their role in rice quality regulation remains unclear. This study used BR-deficient lines (osd11#1 and osd11#2), BR-enhanced lines (OsD11-OE1 and OsD11-OE2), and wild-type rice (Zhonghua 11) to investigate BRs' effects on rice quality. Key enzyme activities (GBSS, SSS, SBE) were analyzed, alongside starch structure characterization (molecular weight distribution, chain length distribution, crystallinity) and functional properties (thermal behavior, swelling power, solubility, digestibility). The results showed that in BR-enhanced lines, GBSS, SSS, and SBE activities all increased, with GBSS exhibiting the greatest extent, thereby increasing amylose and short-chain amylopectin proportions while reducing long-chain amylopectin proportions. These lines also displayed lower starch crystallinity, gelatinization temperature, and digestibility, ultimately improving rice quality compared to wild-type. However, BR-deficient lines exhibited the opposite trends in these parameters. These findings indicate that BRs regulate amylose more sensitively than amylopectin and are important regulators of high-amylose premium rice.