Identification Of QTL And The Genetic Basis Dissection For Protein And Amino Acid Content In Milled Rice

Protein is the second most abundant constituent of milled rice, following starch. As one of the staple food, rice is one of the most important protein sources for people. Because of the relative complication in evaluating protein and amino acid content compared to other quality traits in rice, it is difficult to improve the content of protein and amino acid by conventional breeding. With the advent of molecular marker, introgression of genes controlling good quality by marker-assisted selection has been proved to be an effective choice to improve the quality of cultivars. However, the genetic basis of protein and amino acid content is complex and often controlled by quantitative trait loci. Thus, mapping those QTL underlying protein and amino acid content is needed for rice genetic improvement. In the years of 2004 and 2005, the phenotypes of protein content, 17 kinds of amino acid content and total amino acid content were collected using the F₉ RIL population from the cross between ZS97B and DL208. The main results were as follows:1. The result of t-test showed that the protein content, 17 kinds of amino acid content and total amino acid content of ZS97B were significant higher than those of DL208 with the threshold of p=0.01 in the two years of 2004 and 2005.2. Significantly positive correlations were found between 2004 and 2005 in the same trait. The correlation of protein content was the least, followed by tyrosine, glysine, total amino acid, threonine, alanine, glutamic acid. The relatively lower heritability of protein content in rice implied that the heritability of protein content was more sensitive to environmental change than that of amino acid content. And also significantly positive correlations were found between all amino acid content and protein content.3.49 and 65 QTL were identified in 2004 and 2005 respectively. The contribution of each QTL to the phenotypic variation varied from 4.0% to 43.7%. Most QTL co-localized, forming 29 QTL clusters on the chromosomes, with three major ones detected in both years and mapped on chromosome 1, 7, 9. And the two QTL clusters in the interval of RM493-RM562 on chromosome 1 and MRG186-MRG4499 on chromosome 7 influenced almost all the traits, with the allele from Zhenshan 97B decreasing and increasing the phenotype respectively. The QTL in the interval of RM328-RM107 on chromosome 9 detected in both years influenced the lysine content, with the allele from Delong 208 increasing the lysine content.4. QTL analysis was carried out by the software QTLMapper 1.6, using the data from the integration of the two years. A mixed linera model approach was applied to detect QTL, digenic and environmental interactions for the protein content. The result was that additive effect was the dominant genetic component for all the traits, and epistatic interactions and environment efects are also important to influence the traits. The heredity was changed by the differences of genetic background and environment.5. A wide coincidence was found between the QTL detected in our research and the loci involved in amino acid metabolism pathways in N assimilation, transfer, or protein biosynthesis. For example, in the interval of seven QTL clusters of our results, 15 genes including two genes for N assimilation and transfer, 7 genes for amino acid metabolism, and 6 genes for protein biosynthesis were found. There were several genes corresponding to one QTL sometimes. The results will be very useful for identifying candidate genes and marker-assisted transference of the favorable allele in rice breeding programs.