Decreased gelatinization and retrogradation promoting cold storage stability in glutinous rice via low SSIIa...

Gelatinization, retrogradation and storage stability are crucial properties affecting glutinous rice consumption and flour processing. However, the molecular mechanisms governing these processes, particularly the key genetic and structural determinants, remain largely elusive. Here, we identify SSIIa as a key regulator governing gelatinization and retrogradation properties in glutinous rice by targeted-gene association study. The resultant enhancement of SSIIa enzyme activity in glutinous rice varieties with SSIIa^Hap3 or SSIIa^Hap4 contributes to increased amylopectin B1 chains, starch molecular weight, crystallinity, and structural order, which ultimately generates higher gelatinization temperature (GT) and retrogradation rate (R%). On the contrary, low-activity of SSIIa in SSIIa^Hap1 or SSIIa^Hap2 varieties results in lower GT and R%. Additionally, long-term cold storage (4°C) substantially affects starch retrogradation in an SSIIa-dependent manner, but does not alter GT. Glutinous rice varieties with low SSIIa activity significantly reduce in ∆Hr and R% after cold storage. Our finds clarify the mechanism of gelatinization and retrogradation of glutinous rice starch, and providing key information for targeted breeding with low GT and low R% as well as a new way to suppress deleterious retrogradation during storage.