Double repression of soluble starch synthase genes SSIIa and SSIIIa in rice (Oryza sativa L.) uncovers interactive effects on the physicochemical properties of starch

Abstract

Soluble starch synthases (SSs) are major enzymes involved in starch biosynthesis in developing rice (Oryza sativa L.) endosperm. Despite extensive studies of SSs in various plant species including rice, the functional modes of action among multiple SS genes are still not clear. Here, we generated transgenic RNA interference (RNAi) repressed lines for seven of the eight members of the rice SS gene family and studied their effects on starch synthesis and grain formation. Consistent with their expression domains, RNAi repression of genes that encode isozymes SSI, SSIIa, and SSIIIa had strong effects on grain development, whereas no obvious phenotypic changes were observed in transgenic plants with the other SS genes being RNAi repressed, indicating functional redundancies among the genes. To study the potential functional interactions of SS genes, we generated SSIIa/SSIIIa double repression lines whose kernels displayed a chalky kernel appearance and had increased amylose levels, increased pasting temperatures, and decreased viscosities. The double mutation also reduced short (degree of polymerization (DP) 5-6) and long (DP 12-23) amylopectin chain contents in the grain and increased the medium long types (DP 7-11). The nonadditive nature of the double mutation line suggests that SSIIa and SSIIIa interact with each other during starch synthesis. Such interaction may be physical via starch phophorylase as indicated by our pair-wise yeast two-hybrid assays on major starch synthesis enzymes. Collectively, the data showed that SSIIa and SSIIIa play distinctive, but partially overlapping, roles during rice grain starch synthesis. The possibility of extensive redundancy or complementarity among SS isozymes is discussed.

Alanine aminotransferase 1 (OsAlaAT1) plays an essential role in the regulation of starch storage in rice endosperm

“…RNAi repression of SSIIa and SSIIIa also influences the formation of grains, making their appearance chalky [45]. Those reports support our conclusion that the phenotypes for our osalaat1 mutants are likely due to reduced expression of the starch synthase genes.…”

Critical roles of soluble starch synthase SSIIIa and granule-bound starch synthase Waxy in synthesizing resistant starch in rice

“…S3 A-C), and these findings are consistent with the previous report of increased amylose in starch of flo5 mutants (21). The increase in PT is consistent with previous report in SSIIIa RNAi (24), whereas the reported decrease in gelatinization temperature (21) is apparently inconsistent with the observed increase in PT (Fig. S3C); these results could be attributed to the use of different techniques of differential scanning calorimetry and Rapid Visco Analysis, respectively.…”

Population structure and association analysis of yield and grain quality traits in hybrid rice primal parental lines

“…htm). AC is mainly controlled by Wx, SSIIa, and SSIII (Fujita et al 2007;Sato et al 2002;Zhang et al 2011a). Wx is a pleiotropic gene, which also regulates GC.…”