Effects of Wx and Its Interaction With SSIII-2 on Rice Eating and Cooking Qualities

Abstract

The Wx gene encodes a granule-bound starch synthase (GBSS) and plays a key role in determining rice eating and cooking qualities (ECQs). SSIII-2 (SSIIIa), a member of the soluble starch synthases, is responsible for the synthesis of long chains of amylopectin. To investigate the effects of Wx and its interaction with SSIII-2 on grain ECQs, a population from a hybrid combination was established as a research material. The genotypes of SSIII-2 and the single nucleotide polymorphisms (SNPs) on intron1, exon6, and exon10 of Wx, and the physicochemical indicators and rapid visco analyzer (RVA) profile characteristics were analyzed. The results revealed various effects of SSIII-2 on rice quality under different backgrounds of Wx alleles. There was no obvious difference between different SSIII-2 alleles under the same background of Wx^a , whereas there was a significant diversity under the same background of Wx^b . Wx^a had a dominant epistasis to SSIII-2 because the effect of SSIII-2 was masked by the massive synthesis of GBSS under Wx^a . The apparent amylose content (AAC) was mainly controlled by the In1G/T SNP, and rice gel consistency (GC) was regulated by the Ex10C/T SNP. The combined effects of three SNPs had a significant influence on all ECQs and RVA profile parameters, except for gelatinization temperature. In1T-Ex6A-Ex10C and In1T-Ex6A-Ex10T were classified as being low AAC type. TT-AA-CC and TT-AA-TT had a low AAC and a soft GC. The combined effects of different SNPs of Wx are very important for rice quality breeding.

Keywords: SSIII-2; Wx; eating and cooking qualities; epistasis; rice (Oryza stativa L.); single nucleotide polymorphism.

Figure 1

RVA profile characteristics for different haplotypes of In1G/T and Ex6A/C polymorphisms of Wx. (A) Peak viscosity (PKV). (B) Hot paste viscosity (HPV). (C) Cool paste viscosity (CPV). (D) Breakdown valve (BDV). (E) Setback valve (SBV). (F) Consistency valve (CSV). (G) Pasting temperature (PaT). (H) Pasting time (PeT). GG-AA, GG-CC, GT-AA, GT-CC and TT-AA represent different haplotypes of In1G/T and Ex6A/C polymorphisms of Wx. Lowercase and capital letters above column denote significant at 0.05 and 0.01 levels, respectively.

Figure 2

RVA profile characteristics for different haplotypes of In1G/T and Ex10C/T polymorphisms of Wx. (A) Peak viscosity (PKV). (B) Hot paste viscosity (HPV). (C) Cool paste viscosity (CPV). (D) Breakdown valve (BDV). (E) Setback valve (SBV). (F) Consistency valve (CSV). (G) Pasting temperature (PaT). (H) Pasting time (PeT). GG-CC, GG-TT, TT-CC, TT-CC, GT-CC and GT-TT represent different haplotypes of In1G/T and Ex10C/T polymorphisms of Wx. Lowercase and capital letters above column denote significant at 0.05 and 0.01 levels, respectively.

Figure 3

RVA profile characteristics for different haplotypes of Ex6A/C and Ex10C/T polymorphisms of Wx. (A) Peak viscosity (PKV). (B) Hot paste viscosity (HPV). (C) Cool paste viscosity (CPV). (D) Breakdown valve (BDV). (E) Setback valve (SBV). (F) Consistency valve (CSV). (G) Pasting temperature (PaT). (H) Pasting time (PeT). AA-CC, AA-TT, CC-CC and CC-TT represent different haplotypes of Ex6A/C and Ex10C/T polymorphisms of Wx. Lowercase and capital letters above column denote significant at 0.05 and 0.01 levels, respectively.

Figure 4

RVA profile characteristics for different haplotypes of In1G/T, Ex6A/C and Ex10C/T polymorphisms of Wx. (A) Peak viscosity (PKV). (B) Hot paste viscosity (HPV). (C) Cool paste viscosity (CPV). (D) Breakdown valve (BDV). (E) Setback valve (SBV). (F) Consistency valve (CSV). (G) Pasting temperature (PaT). (H) Pasting time (PeT). GG-AA-CC, GG-AA-TT, GG-CC-CC, GG-CC-TT, TT-AA-CC, TT-AA-TT, GT-AA-TT, GT-AA-TT, GT-CC-CC and GT-CC-TT represent different haplotypes of In1G/T, Ex6A/C and Ex10C/T polymorphisms of Wx. Lowercase and capital letters above column denote significant at 0.05 and 0.01 levels, respectively.