| Rice quality improvement has become one of the most important goals in rice breeding programs. Percentage of grains with chalkiness (PGWC) is one of the most important of rice appearance quality. Grain chalkiness is not only associated with poor rice appearance quality, but also with high levels of damage to the kernel during milling and reduction of eating and cooking quality. High PGWC has become a major reason of low rice quality of rice varieties in our country, especially for hybrid rice. In this study, we have got a chromosome segment substitution line with high PGWC, CSSL50, derived from Asominori (japonica)/IR24 (indica) with Asominori as the recurrent parent. The mapping population was constructed from the cross between CSSL50 and parent line, Asominori. Trait of PGWC was used for characterization, genetic analysis, primary mapping and high resolution mapping QTL analysis. Differences of other quality components and physicochemical characteristic of starch between Asominori and CSSL50 were investigated.The main conclusions are as follows:1. There were not significant differences in grain shape (including grain length, grain width and grain length-width ratio), thousand grain weight (TGW) and brown rice ratio (BR) between CSSL50 and Asominori; the milled rice ratio (MR) and head rice ratio (HR) of CSSL50 were significant and high significant reduced, comparing Asominori (P values were 0.0457 and 0.0002, respectively); there were significant negative correlation between PGWC and MR and HR, the coefficient of correlation were-0.8451 and-0.9894, respectively. The appearance amylose content (AAC) and protein content (PC) of CSSL50 were 23.7%and 14.2%higher than of Asominori. Significant difference was observed in the degree of polymerization (DP) between CSSL50 and Asominori. The chains of DP 8-14 decreased, while the chains of DP< 8 or DP>14 increased, these might be one of the reason of grain chalky. The RVA was used for cooking and eating quality analysis. The peak viscosity (PKV), hot paste viscosity (HPV), cool paste viscosity (CPV) and breakdown (BDV) of CSSL50 were significant higher than of Asominori, while the consistence (CSV) and setback (SBV) were lower. They were associated with the grain chalkiness.2. The QTLqPGWC-8 could be detected between the marker RM7356 and RM7556 on the chromosome 8 using the Win QTL Cartographer 2.5 and IciMapping v2.2 softwares in the BC4F2 secondary separation of groups, derived from the crossing between the high PGWC line-CSSL50 and the background parent Asominori. The qPGWC-8 has a PVE (%, phenotypic variance explained) of 43.9%and 33.1%with the LOD of 34.1 and 44.5, using the different softwares. A serious sub-NILs with different chromosome segment substitution between the markers RM7580 and RM6976 were developed to identify the qPGWC-8, and the QTLqPGWC-8 was dissected into a single gene, the qPGWC-8 allele in IR24 could increase PGWC in the Asominori background in an additive fashion. The additive effect of the IR24 was 26.6%and the IR24 allele was incompletely dominant.3. The qPGWC-8 gene was narrowed down to a candidate genomic region of 142 Kb long defined by InDel markers 8G-7 and 8G-9 on the chromosome 8, by using the 7910 BC4F3 plants developed from the BC4F2 plants, which had the Asominori/IR24 heterozygous segment between RM7580 and RM6976. The overlapping chromosome analysis was used to identify the region of gene. The BC4F4 plants were used to identify the phenotypes of recombinant plants. Finally, the qPGWC-8 was further mapped between the 8G-35 and 8G-9, with a 32 Kb region, using InDel markers developed in our laboratory. Based on the available sequence annotation (http://www.ncbi.nlm.nih.gov/BLAST), there were 5 predicated candidate genes in the target region. Among these genes, two were putative proteins, and the corresponding proteins of the other two genes with functional annotation include 1) D-3-phosphoglycerate dehydrogenase; 2) SGT1 protein; 3) serine esterase family protein.4. The expression of ORF2 was significant enhanced in the CSSL50 by RT-PCR, which was consistent with the results of gene chip in our lab. So, we put the ORF2 as the candidate gene for the qPGWC-8, temporary. The ORF2 was coding the D-3-phosphoglycerate dehydrogenase (OsPGDH). This gene was constitutive expression in all tisses, such as root, shoot, leaf, sheath and endosperm, using the Real-time Quantitative Chain Reaction, and the higher expressions were found in the sheath and root. In the development of endosperm, the expressions were relative higher in the prophase (6d after flowering,6 DAF) and the later stage (20 DAF), but relative lower in the middle stage. The expression of OsPGDH in the CSSL50 was significant higher than in the Asominori during the development of endosperm. |
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