The Effects Of Allelic Alteration Of Genes Responsible For Amylopectin Synthesis On Starch Physicochemical Properties In Rice (Oryza Sativa L.)

In order to investigate the effects of the allelic alteration of some genes responsible for amylopectin synthesis on the starch physicochemical properties in rice (Oryza sativa L), several candidate individuals containing the specific combination of starch synthesis-related genes were selected by using the gene-tagged molecular markers from a BC2F4 population, which is derived from a indica variety with poor quality, Guichao 2, as the recurrent parent and a japonica waxy variety with good quality, Suyunuo, as the donor parent. Each of the selected plants were detected to carry the alleles of starch-synthesizing genes from Guichao 2 except for only one gene from Suyunuo. Some of them was crossed with each other to generate the F1 hybrids, and three F₂ populations, each contained the relatively consentaneous genetic background except for the target gene(s), were subsequently obtained. The starch physicochemical properties of the mature seeds, as well as the mRNA expression level of several target genes in the developing seeds, were carefully measured and compared among the selected individuals from the developed F₂ population, and the main results were shown as followings:1. Based on the sequence diversity between indica and japonica subspecies available online, the gene-tagged molecular markers were developed for Sssâ…¢-1 and Sssâ…£-1 genes, respectively.2. The allelic difference of Sbe1 gene between two rice cultivars had a significant effect on the apparent amylose content (AAC) and gel consistency (GC), but not on the gelatinization temperature (GT). In details, in the selected individuals from the F₂ population, in which the allele of Sbe1 gene (Sbe1g) from Guichao 2 was substituted by that (Sbe1s) from Suyunuo, the AAC was significantly lower, while GC was harder, when compared with that of those still carrying the Sbe1g allele from the recurrent parent. Besides, the subtitution of Sbe1 gene also had an effect on the starch viscosity profile detected by the Rapid Visco Analyser (RVA). In particular, it was lower on the peak ciscosity (PKV), hot viscosity (HPV) and cool viscosity (CPV), in the individuals containing the Sbe1s allele than those with the Sbe1g allele.3. In the case of Sssâ…¢-1 gene, there were significant effects of the allelic alteration on GC and several starch viscosity characteristics, but no on AAC and GT. When the Sssâ…¢-1g allele was substituted by Sssâ…¢-1s, the GC tended softer, while the three primary RVA measurements (PKV, HPV and CPV) and the consistency value (CSV) became higher.4. There was no significant difference on the starch physicochemical properties of rice seeds between the individuals of F₂ population containing the different allele of Sssâ…£-1, Isa or Pul gene, respectively.5. Among the F₂ population derived from the cross between the individual plant containing the genotype of Sbe1s Sbe1s Sssâ…¢-1g Sssâ…¢-1g and that of Sbe1g Sbe1g Sssâ…¢-1s Sssâ…¢-1s (ab. Sbe1/Sssâ…¢-1 F₂ population), it was higher of the mRNA expression level of Sbe1 and Sssâ…¢-1 genes in developing endosperm of the selected individuals with Sbe1s allele than those with Sbe1g allele. According to the fact that the AAC was significantly lower in the same individuals with Sbe1s allele than that with Sbe1g allele, it implied that there might be a tight relationship between the expression of the target genes and the synthesis of amylopectin.6. The interaction was detected among the different genes responsible for amylopectin synthesis, and such interation also affected the starch physicochemical properties. For an example, a significant effect of the interaction between Sbe1 and Sssâ…¢-1 genes was detected on the GT, CPV, CSV and SBV. Besides, the results from the expression analyses showed that the alteration of the Sssâ…¢-1or Sbe1 allele could affect the expression of Sbe1 or Sssâ…¢-1 gene, respectively, while the change of the Isa allele had an effect on the expression of Sssâ…£-1 gene.