ABA associated OsSWEET1A-mediated sucrose transport to drive high daily yield and high efficiency carbon allocation in ratoon season rice

Contexts Ratoon season rice utilizes axillary buds remaining after main-season harvest to produce a second crop without replanting, offering high daily yield, resource savings, and notable economic benefits. However, the physiological and molecular bases for its superior productivity remain unclear. Objectives This study aimed to elucidate the physiological and molecular basis for the high daily yield and high efficiency of ratoon season rice. Methods In 2023–2024, we compared main crop season rice (MC), ratoon season rice (RR), and late-season rice (LR) synchronized at heading, using four varieties. Parameters measured included grain yield, economic benefit, non-structural carbohydrate (NSC) remobilization, 13 C-assimilate partitioning, grain-filling traits, activities of key carbon-metabolizing enzymes, endogenous hormone levels, and transcriptome profiles. Results Over two years, RR produced significantly more panicles, higher seed-setting rates, and greater 1000-grain weight than MC and LR. Its daily grain yield was 34.8–73.9% higher, and 1000-grain weight increased by 1.6–12.8%. Mechanistically, RR showed a 66.8–153% higher NSC translocation rate from stems and a 24.3–51.3% greater 13 C allocation to grains compared with MC and LR. Grain-filling analysis further showed that RR accelerates the filling of inferior grains by coordinating the rate and duration of filling, and correlation and path analyses revealed that an early sucrose peak and rapid starch accumulation directly enhance the maximum filling rate and prolong the active filling duration, thereby increasing grain weight. This was associated with elevated abscisic acid (ABA) and up-regulated OsSWEET1A expression in RR, which may facilitate photo-assimilate delivery to grains. Conclusion These findings reveal the physiological and molecular basis for the high daily yield and high efficiency of ratoon season rice. Significance They also provide theoretical guidance for cultivation optimization and candidate gene resources for breeding programs.