QTL Mapping And Meta-analysis Of Kernel Morphology-related Traits In Wheat

Kernel morphology is one of important components for quality and yield performance in wheat crops.Its inheritance is controlled by polygenes and easily interacted with environments,indicating the genetic nature of complex quantitative trait.Previous studies on kernel morphology-related traits mainly highlighted in identifing additive quantitative trait loci(QTL),but ignored the genetic dissection of epistatic effects and the interactions between QTLs and environments.In addition,due to the strong influence of genetic backgrounds and environments,it is difficult to find true and stable QTLs reported in early studies.Therefore,further analysis of the genetic basis of kernel morphology-related traits and find consistent QTLs will be of great significance for the molecular marker-assisted selection breeding and genetic improvement in kernel morphology-related traits in wheat.In this study,the recombination inbred lines(RIL)developed by the two winter wheat varieties,Longjian 19 and Q9086,contrasting with drought tolerance and kernel morphology,were used as plant materials.QTL mapping together with genetic dissection were performed for kernel morphology-related traits under different water environments.Furthermore,the meta-analysis was conducted by collecting identified QTLs herein and reported QTLs for kernel length,kernel width and thousand grain weight,which would further narrow the confidence interval of target QTLs and obtain consistent QTLs.According to the annotation of the wheat reference genome,candidate genes were predicted in the meta QTL(MQTL)segments.The fidings will provid theoretical basis for QTL fine mapping and gene cloning for kernel morphology-related traits in wheat.The results are as follows:1.Kernel morphology-related traits,such as kernel length,kernel width,kernel thicken,kernel length-with ratio,kernel perimeter,kernel area and thousand grain weight,showed continuous variations and transgressive segregation in the RIL population,indicating these traits were controlled by polygenes and easily interacted with environments with a complex genetic pattern.2.A total of 35 additive QTLs(A-QTLs)and 122 pairs of epistatic QTLs(AA-QTLs)were located on 21 chromosomes of wheat under different environmental conditions,individually accounted for of 3.60%~13.90% and 0.29%~2.76% of phenotypic variance,respectively.These QTLs had positive or negative effects on phenotypic variations in kernel morphology-related traits.Three main-effect loci(Qkl.acs-1B.1,Qkw.acs-6A.1 and Qkp.acs-1B.1)were found in A-QTLs that explained more than 10% of the phenotypic variance.No A-QTLs was repeatedly expressed in two environments.These A-QTLs and AA-QTLs had significant interactions with water environments,but genetic contributions to phenotypic variation were lower(<3.05%).3.Seven QTLs hot spots were found in marker intervals of Xwmc206-Xmag981 on chromosome 1B,Xwmc231-Xgwm284 on 3B,Xbarc59-Xbarc232 on 5B,Xgwm149-Xgwm495 on 4B,Xgwm186-Xcfa2185 on 5A,Xgwm292-Xwmc161 on 5D and Xbarc171-Xgwm427 on 6A.4.A total of 337 A-QTLs reported early were collected for kernel morphology-related traits and 59 MQTLs were finally identified by the meta-analysis using the software of BioMercator4.2.Of these MQTLs,there were 19 for kernel length,14 for kernel width,and 26 for thousand grain weight.The minimum confidence interval reduced to 0.6 cM,and the minimum map distance was shortened within 2.4 cM,which significantly improved the accuracy of QTL mapping.Some QTL clusters were located in marker intervals of Xwmc661-Xrz444.1 on chromosome 2B,Xbarc124-Xcfd50 on 2D,Xgwm165.3a-Em4Me13 on 4B and Me6Em5-Xwmc622 on 4D.This indicated that these chromosomal regions highly concentrated on majorQTLs and suggested pleiotropy in the inheritance of these traits.In addition,these chromosomal regions could harbor key genes governing grain length,grain width and thousand grain weight.5.According to locations of MQTLs on the physical map of wheat chromosomes,functional annotations by the method of bioinformatics were made to exploid the genes associated with MQTL15 for the kernel length,MQTL14 for kernel width and MQTL25 for thousand grain weight.Total of nine candidate genes related to kernel morphology and thousand grain weight were found.In this study,using molecular quantitative genetics and meta-analysis methods,the genetic basis of wheat kernel morphology-related traits under different water environments was analyzed,some consistent QTLs and candidate genes were discovered.The fidings would be of great importance to the molecular marker-assisted selection breeding and genetic improvement in wheat kernel morphology-related traits,especially under water-stressed environments.