Fine Mapping And Candidate Gene Prediction Analysis Of Gray Leaf Spot Resistance Gene QTL-qGLS4 In Maize

Gray leaf spot（GLS）,caused by Cercospora zeae-maydis,is one of the most serious maize leaf diseases in the world,which seriously reduces maize yield.Therefore,planting and breeding disease-resistant varieties are the most effective and economical to prevent the occurrence and prevalence of maize gray leaf spot and prevent maize yield reduction.Based on the preliminary mapping results,we used the donor parent high resistance inbred line T32 and the recipient parent high sensitivity inbred line J51 to obtain the BC₃F₂ and BC₄F₂ near-isogenic line through hybridization,backcrossing,molecular marker-assisted selection and genetic background selection.In this study,we used initial localization markers umc1173-umc1101 to find published polymorphic primers,combined with seven pairs of newly designed polymorphic primers to construct genetic linkage maps,and used population genotype and phenotypic data to fine mapping QTL-qGLS4.The results are as follows:（1）In the BC₃F₂-MS1 near-isogenic line（180 individual BC₃F₂ subpopulations obtained by self-crossing of BC₃F₁ generations,named BC₃F₂-MS1）,polymorphism primers were developed according to the umc1643a and umc1101 markers and seven pairs of newly developed primers.The target segment of the QTL was located in the jz30-jz50 marker interval.The physical distance was shortened from 1790.369kb to 157.417kb,the explained phenotypic contribution rate was6.29%,and the additive effect value of QTL was-0.96,indicating that the synergistic gene was derived from parent T32,and the gene mode of action was overdominant（OD）.In the BC₄F₂-MS near-isogenic line（180 individual BC₄F₂ subpopulations were constructed by self-crossing BC₄F₁population and named BC₄F₂-MS）,a genetic linkage map was constructed according to the umc1173 and umc1101 markers and seven pairs of newly developed polymorphic primers.Combined with the phenotypic data of BC₄F₂-MS population,the target segment of the QTL was also located in the jz30-jz50 marker range,with a physical distance of 157.417kb.The explained phenotypic contribution rate was 10.66%,and the additive effect value of the QTL was-0.09,indicating that all the synergistic genes were derived from the parent T32.The gene mode of action was additive effect（A）,and the results of BC₃F₂-MS1 population localization were further verified.（2）In the BC₄F₂ near-isogenic line（containing 1391 individual plants）,QTL-qGLS4 was finely mapped to the jz30-jz50 marker with a physical distance of 157.417kb combined with the BC₄F₂ genotype and phenotype,which explained 22.44%of the phenotypic contribution of resistance to gray leaf spot,and the additive effect value was-1.30.The mode of gene action is additive（A）.In this study,multiple comparison of single plant phenotypes of BC₃F₂-MS1,BC₄F₂-MS and BC₄F₂ near-isogenic line population further indicated the existence of QTL for maize gray leaf spot resistance between jz30 and jz50.（3）Fine mapping defined QTL-qGLS4 between SSR markers jz30-jz50.There were 10prediction genes in maize B73 genome within 157.417 kb.The prediction analysis showed that,Zm00001d053724（uncharacterized）,Zm00001d053726（intracellular protein transport protein USO1）and Zm00001d053732（protein CYPRO4）are involved in the regulation of secondary metabolism,growth/development process,abiotic stress response and resistance to pathogen.Therefore,Zm00001d053724,Zm00001d053726 and Zm00001d053732 were predicted to be candidate genes for resistance to maize gray leaf spot QTL-qGSL4.This study provides a new theoretical reference for breeding against maize gray leaf spot,lays a foundation for further studies on gene cloning,function verification and action mechanism,and provides guidance and reference for the research on candidate genes in target regions.