Granule‐bound SSIIa Protein Content and its Relationship with Amylopectin Structure and Gelatinization Temperature of Rice Starch

Starch characteristics such as gelatinization properties determine the quality of various products of rice. The eating, cooking and processing qualities of rice are a function of the gelatinization of rice starch. The gelatinization temperature (GT) of rice is controlled by the starch synthase IIa (SSIIa) gene. In the present study, the amount of the starch‐associated SSIIa protein and its relationship with amylopectin structure and GT were investigated. The results indicated that the starch associated SSIIa protein content was positively correlated with GT and level of amylopectin chains with degree of polymerization 12‐24 (DP12‐24), and negatively correlated with the fraction of chains with DP6‐11 and short chain ratio (SCR), i.e. DP6‐11/DP12‐24 (P<0.001). GT was also negatively correlated with DP6‐11 SCR, and positively correlated with DP12‐24. The SSIIa protein content and amylopectin structure showed significant difference between the two SSIIa single nucleotide polymorphisms (SNPs, i.e. guanine‐cytosine/thymine‐thymine (GC/TT)) groups. Rice with GC and TT SNPs had average SSIIa protein contents of 1.076 and 0.681, respectively. Rice with the GC SNPs displayed a lower amount of chains with DP6‐11 and more chains with DP 12‐24 than those with TT SNPs. A mechanism is postulated to explain how SSIIa could determine the distribution of amylopectin side‐chains, which affects the gelatinization temperature of rice starch.