Two Complementary Genes, SBE3 and GBSS1 Contribute to High Amylose Content in Japonica Cultivar Dodamssal

Quantitative trait loci (QTLs) for the starch-related traits amylose content (AC) and resistant starch (RS) content have received much attention due to the potential benefits of grains high in these starch levels. In this study, QTLs associated with AC and RS content were identified using 92 recombinant inbred lines (RILs) developed from a cross between two closely related japonica cultivars ‘Dodamssal’ and ‘Hwayeong’. One QTL on chromosome 2 for RS content and 2 QTLs for AC on chromosomes 2 and 6 were detected. The F2 population derived from a cross between Hwayeong and two selected RILs were used to analyze the interaction between starch branching enzyme 3 (SBE3) and granule-bound starch synthase 1 (GBSS1). The combined effect of SBE3 and GBSS1 in the F2 population suggested that these two genes behaved in an additive manner in increasing AC. Haplotype analysis based on two SNPs in GBSS1 classified 117 rice accessions into three groups. At the first SNP site, all indica, Korean landrace, and weedy rice accessions had the Wxᵅ allele at the 5ʹ splice site of intron 1, whereas japonica accessions had the mutated Wxᵇ allele. This suggests that this splice-donor mutation is prevalent in japonica cultivars, but rare or absent in landrace and weedy rice cultivars. Landrace or weedy rice accessions harboring the Wxᵅ allele could be employed in breeding programs to manipulate AC in cultivated japonica rice considering the difficulty and time to introduce desirable indica traits into japonica due to reproductive barriers.