| Rice is a main cereal food for the population of world and China. Because of the increase of population and food security problem, improving the yield is the most important goals of rice breeding programs in our coutry. However, with the improvement of people’s life quality and the fierce global rice market competition, rice quality improvement has become one of the most important goals in rice breeding programs. Here, two different methods were used:1) QTL analysis was used to search useful natural allele for rice quality.2) mapping cloning of genes underlying mutant for rice quality was used to find the essential elements controling rice quality.Though the fat or oil in rice grain is low (i.e.,2-3%) and concentrated in germ and bran fraction, its unique healthy benefits has been drawing people’s attention. At the same time, it is a key determinant of the processing and cooking quality of rice. So far, the genetic studies on fat had been carried out mainly by classical quantitative genetic methods and single-environment QTL detection. Thus, the genetic information on the environmental stability of QTL, gene action of QTL in the new genetic background, and DNA markers closely linked to target QTL are particularly lacking. To better elucidate genetic basis of rice fat accumulation, Four different populations were used to analysis environmental stablity across different environments. At the same time, we identified the OsGE gene, which can enhance rice fat accumulation by increasing rice embryo size. Besides, we also identified a short grain length mutant (SGL), and the SGL gene were mapped on chromosome 5. The main results are as follows:1. Identification of stably expressed QTL for grain fat accumulationA total of 85 inbred lines derived from the backcross between Sasanishiki (japonica, as the recurrent parent) and Habataki (indica) were used to detect QTL for rice fat acumulation including fat content, brown rice weight and fat index. Five QTL for fat content, three QTL for brown rice weigth and three QTL for fat index were mapped on chromosome 1,3,6,7,10,11 and 12, explained 5.84-28.46% of the phenotypic variance. Then all the QTL for fat content and fat index were further confirmed across two different environments by some chromosome segment substitution lines (CSSLs), where Habataki was used as the donor parent and Sasanishiki as the recurrent parent, except qFI2. Some QTL affecting fat content and fat index were mapped on the same genome regions. Co-localization of these QTL can provide an explanation for the genetic basis of correlation between fat content and fat index.2. Identification of two loci increasing grain fat content in rice and physiological analysis of their function (Oryza sativa)The BIL population and CSSL population derived from Koshihikari and Kasalath were used to analysis stable-expressed QTL across three environments. Two stable QTL (denoted as qFC7.1 and qFC7.2) for fat content with large effect were mapped on chromosome 7 in two population across three environments. Four CSSLs were selected to further analysis. Six-environment data on fat content of the four CSSLs confirmed the effect of qFC7.1 and qFC7.2 with high repeatability. Further analysis of these CSSLs on physiology and biochemistry showed that qFC7.1 and qFC7.2 can enhance rice storage fat and embryo fat without other adverse effects. To obtain a CSS line only harboring qFC7.1, we developed a SBC3F2 population (n=2000) from Koshihikari and SL220 pryminding qFC7.1 and qFC7.2. we selected three SBC3F2 lines only habording qFC7.1 by MAS. T-test derectly confirmed the present of qFC7.1. In our marker interval of qFC7.2, we found there was a candidate gene encoding 3-oxoacyl-[acyl-carrier-protein], which played a role on fat synthesis. cDNA sequence blast showed that there was some single nucleic acid difference between Koshihikari and Kasalath. All these results can help us for further study on genetic basis of rice fat.3. Mapping cloning of OsGE gene which can can enhance rice fat accumulation by increasing rice embryo size.Embryo size-related genes can be used for enchancing rice grain nutrition, especially rice fat. w025 is a new variety derived from chemical inducement and cross breeding method. It is characteristic for its giant embryo. To investigate the effects of embryo size, we conducted microscopy analysis. The result showed that w025has an enlarged scutellum. To map the ge locus, we generated F2 mapping population derived from a cross of the w025 and the cultivar 9311. We mapped the ge to an interval between RM21930 and RM234 on Chromosome 7. To narrow down the search for a candidate gene affected in ge, a larger F2 mapping population consisting of more than 10000 plants, of which 1000 segregants showing the ge mutant phenotype were used for fine-mapping. Between markers RM516 and RM164, we further developed one SSR marker and two InDel markers. The ge locus was finally located in a 95-kb DNA region between SSR marker RM21930 and InDel marker InDelE. In this interval, a gene related with embryo size was collected by NCBI. To define the molecular lesions of ge mutant, the ORF from from wild type and w025 were amplified by RT PCR and were sequenced. Comparison of the sequences revealed that the ORF carries a single nucleotide mutation, which cause premature termination, resulting in a truncated polypeptide.4. primary mapping of SGL geneIn our study, we also isolated a short grain length mutant (SGL). Comparing with wildtype Kitaaki, SGL has distinguished phenotype on grain size, panicle characters, heading date and plant height. Since SGL was derived from transgene lines, the TAIL-PCR was used to analysis the gene which was knocked out by exogenous DNA. The result showed that the knock-out gene is mapped on chromosome 1and encode a polyprotein. To map the SGL locus, we generated F2 mapping population derived from a cross of the SGL and the cultivar G46B. Then We mapped the SGL to an interval between G5-9 and 1510 on Chromosome 5, a 127-kb DNA region. These results are useful in map-based cloning of GSL gene. |
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