Microsatellites, single nucleotide polymorphisms and a sequence tagged site in starch-synthesizing genes in relation to starch physicochemical properties in nonwaxy rice (Oryza sativa L.)

Starch characteristics determine the quality of various products of rice, e.g., eating, cooking and processing qualities. Our previous study indicated that molecular markers inside or close to starch synthesizing genes can differentiate the starch properties of 56 waxy rices. Here we report microsatellite (or simple sequence repeat, SSR) polymorphism in the Waxy (Wx) gene, soluble starch synthase I gene (SS1) and starch branching enzyme 1 gene (SBE1), single nucleotide polymorphism (SNP) in Wx and starch branching enzyme 3 gene (SBE3), and a sequence tagged site (STS) in starch branching enzyme 1 gene (SBE1) among 499 nonwaxy rice samples and their relationships with starch physicochemical properties. The nonwaxy rice samples consist of landraces (n = 172) obtained from germplasm centers and cultivars and breeding lines (n = 327) obtained from various breeding programs. Ten (CT) n microsatellite alleles, (CT)₈, (CT)₁₀, (CT)₁₁, (CT)₁₂, (CT)₁₇, (CT)₁₈, (CT)₁₉, (CT)₂₀, (CT)₂₁, and (CT)₂₂, were found at the Wx locus, of which (CT)₁₁ was the most frequent, and (CT)₁₂, (CT)₂₁ and (CT)₂₂ were identified for the first time. Four (CT) n microsatellite alleles were found at the SBE1 locus, (CT)₈, (CT)₉, and (CT)₁₀ together with an insertion sequence of CTCTCGGGCGA, and (CT)₈ alone without the insertion, of which (CT)₉ and the insertion was a new allele identified in only one rice, IR1552. Multiple microsatellites clustered at the SS1 locus, and in addition to the three alleles previously detected (SSS-A = (AC)₂...TCC(TC)₁₁...(TC)₅C(ACC)₁₁, SSS-B = (AC)₃...TCT(TC)₆...(TC)₄C(ACC)₉, and SSS-C = (AC)₃...TCT(TC)₆...(TC)₄C(ACC)₈), one new allele (SSS-D = (AC)₂...TCC(TC)₁₀...(TC)₄C(ACC)₉) was found. Analysis of the starch physicochemical properties of the samples with different microsatellites, SNPs and STS groups indicated that these molecular markers can differentiate almost all the physicochemical properties examined, e.g., apparent amylose content (AAC), pasting viscosity characteristics, and gel textural properties. Wx SSR and Wx SNP alone explained more variations for all physicochemical properties than the other molecular markers. The total six markers could explain 92.2, 81 and 86% of total variation of AAC, gel hardness (HD), and gel cohesiveness (COH), respectively, and they could explain more than 40% of the total variation of hot paste viscosity (HPV), cool paste viscosity (CPV), breakdown viscosity (BD), setback viscosity (SB) and gel adhesiveness (ADH). However, only 29% of the total variation of peak viscosity (PV) and 37% of pasting temperature (PT) could be explained by all the molecular markers. Some of these markers can differentiate the starch physicochemical properties among the rice samples with the same Wx allele, indicating that the variation within Wx allele classes can be explained by other starch synthesizing genes. These SSRs, SNPs and STS are useful in marker-assisted breeding for the improvement of starch quality of rice.