QTL Mapping For Color-related Traits Of Whole Flour In Wheat And Phylogenetic Analysis Of PDS Genes

Wheat (Triticum aestivum L.,2n=42, AABBDD genome) is one of the most importantstaple crops in China and worldwide. Wheat flour color, which is highly related to carotenoidsand polyphenol oxidase activity, is important in the assessment of flour quality, particularlythe quality of whole wheat flour. In addition to their role in providing color, carotenoids areimportant in human health and nutrition, as antioxidants and precursor of vitamin A.Quantitative trait locus (QTL) analysis has provided an effective approach to dissectcomplicated quantitative traits into their component loci and allow the study of their relativeeffects on a specific trait. These color-related traits are genetically quantitative, ofteninfluenced by the environment and exhibit high genotype×environment interaction. TheQTLs for carotenoids, including lutein and beta-carotene, were rarely reported. Phytoenedesaturase (PDS) is a key limiting velocity enzymes of synthetization of carotenoids. ThePDS genes of wheat relative genus and the phylogeny of plant PDS genes, were rarelyreported. In the present study, QTL mapping for the lutein content (LUC), beta-carotenecontent (BCC), L~*value (LV), a~*value (AV), b~*value (BV) and polyphenol oxidase activity(PPOA) of the whole wheat flour was conducted using a set of recombinant inbred lines(RILs) derived from the cross 'Chuan35050×Shannong483' in three different environmentsand their mean values (MV). PDS genes were cloned from wheat and its relative genus. Thephylogeny of plant PDS genes were analysed using PDS genes cloned by us and those fromGenBank. The mian results are as follows.1) Analysis of phenotypic variation and simple correlation. The variance for eithergenotype or environment effects on all six investigated traits were significant (p≤0.01).There were transgressive segregations for almost all of the traits in the three environments,and continuous distributions were obtained for all of the traits in the three environments,demonstrating the quantitative nature of polygenic inheritance. The hB2values for LV and BVwere over50.0%. The LUC had significant positive correlations with the BCC/BV/PPOA,but significant negative correlations with the LV/AV. The LV had significant negative correlations with the AV/BV/PPOA. A significant negative correlation was found betweenthe BCC and AV, and a significant positive correlation was found between the BV and PPOA.The correlations between the LUC and AV, the BCC and LV/BV/PPOA, and the AV andBV/PPOA were not significant.2) Analysis of QTLs for color-related traits. A total of77QTLs for the six traits werelocated on20chromosomes (all chromosomes except for1D) in the three environments andMV. Of these QTLs,14were found in both environment(s) and MV, and the other63QTLswere found only in the environment(s) or MV. A single QTL in an environment explained3.9to48.7%of the phenotypic variation. The highest LOD was11.9for LV in the MV. Theincreasing effects for36of the QTLs were obtained from Chuan35050, whereas theincreasing effects of41QTLs came from Shannong483. There were9,17,13,12,13and13QTLs found for LUC, BCC, LV, AV, BV and PPOA, respectively. Fifteen QTLs weredetected in at least two environments or in at least one environment and the MV. Of theseQTLs, three QTLs (QLv-6A.1, QBv-1A.2and QBv-6A.1) were detected in all environmentsand MV, two QTLs (QLuc-5B and QLv-2B) were detected in two of the environments andMV, and one QTL (QLv-2D.2) was detected in two of the environments, indicating that theywere relatively 'stable' QTLs. Moreover, the average contributions of QLv-2B, QLv-2D.2andQLv-6A.1were as high as14.6,20.6and18.6%, respectively, indicating that these should bemajor QTLs. Seventeen QTL clusters were mapped on12chromosomes. Seventeen QTLclusters were mapped on12chromosomes. Of the QTL clusters, three (C4, C8, C13) weremore important and the markers near these loci should be useful in marker-assisted selection(MAS).3) Cloning of PDS genes in wheat and its related genus, and phylogeny of plant PDSgenes. Primers were designed according to PDS gene published in GenBank to clone PDSgenes in wheat and its related genus. The PDS genes were cloned in plants that have AAgenome (T.aestivum, T.boeoticum, T.monococcum, T.persicum, T.dicoccoides andT.araraticum). A diversity of amino acid residue was found between the PDS genes inEinkorn (T.boeoticum, T.monococcum) and other plants (T.aestivum and Emmer). Sequencecomparison and phylogeny were conducted in26PDS genes cloned by us (6) and those gotfrom GenBank (20). High homology was found among these PDS genes in sequences ofDNA and amino acid. Phylogeny analysis indicated that: The phylogeny tree of maximumlikelihood method was more close to the traditional plant classification; The26PDS geneswere divided into3clades: algae, dicotyledons and monocotyledons. The PDS genes ofgramineous plants were relatively conservative. Analysis of adaptive evolution indicated that, positive selection was found at3Q and10A. The selection pressure under PDS genes inmonocotyledons and dicotyledons lower individually.4) Phylogeny analysis of wheat related genus based on EST-SSR. EST-SSR developedfrom wheat and other crops, showed high transferability in bentgrass.29triticeae plants weredivided into three clades based on EST-SSRs: plants that have AA genomes, aegilops genus,and plants with other genomes.