Genome-wide Association Study And Proteomic Analysis For Fusarium Crown Rot Resistance In Common Wheat

Fusarium crown rot(FCR)is a severe and chronic disease in common wheat in many arid and semi-arid regions of the world.In the last few years,the incidence and severity of FCR progressively increased in China,and the disease has currently become a new threat to local wheat crops.To date,wheat germplasm with high degree of FCR resistance are rare worldwide.Although some quantitative trait loci(QTL)conferring FCR resistance has been identified in partial resistant genotypes,the molecular mechanisms behind FCR resistance was still poorly understood.All of these factors seriously restricted the improvement of FCR resistance in wheat.With the significant progress made on wheat genome sequencing,genome-wide association studies(GWAS)are widely employed to identify QTL or genes associated with important traits in wheat in recent years.Protein is the final executor of cell function,and the study of proteins responded to FCR infection is an important supplement tool for identification of candidate genes.Therefore,this study firstly screened the FCR resistance level of wheat germplasm resources from different ecological regions of China,and then investigated the chromosome regions associated with FCR resistance in the population of 358 genotypes.The differentially expressed proteins after FCR infection were also studied by proteomics analysis.The main results are as follows:1.In this study 668 Chinese wheat germplasms,plus two genotypes ’Sunco’ and’Shan253’,which served as resistant and susceptible control,respectively,were evaluated for their FCR resistance at seedling stage in greenhouse.The results showed that 92%of accessions were susceptible,including many elite varieties in the country.Twelve genotypes including‘Shiyou 17’ and ’Shixin 733’ in Hebei Province,’04 Zhong 36’ and’Yangao 21’ in Henan Province,’Huaimai 26 in Jiangsu Province,showed comparable resistance level as the resistant control ’Sunco’.2.Based on the origins and pedigree information of the 668 varieties,a set of 358 varieties or advanced lines with disease index(DI)less than 70 was chosen to assemble the association panel for GWAS analysis in greenhouse at seedling stage and in field at adult stage.The effects of plant height,heading date and panicle type on disease resistance were studied.A moderate correlation between FCR resistance at seedling stage and adult stage were identified.Several varieties such as ’Shiyou 17’,’Shixin 733’,’04 Zhong 36’,’Yangao 21’ and ’Huaimai 26’ showed stable resistance at two stages.The correlations between plant height,heading date and FCR resistance were weak.A novel 13.78 Mb region targeted by five SNPs on chromosome arm 5DL,which is not affected by plant height and heading date,was continually detected at both seedling stage and adult stage.The effects of this region on FCR resistance was confirmed in F2:3 bi-parental populations derived by crossing ’04 Zhong 36’,one of the varieties with the highest level of FCR resistance in the association panel,with another susceptible Chinese variety ’Liangxing 518’.A total of 175 candidate genes were identified based on genes annotated in the Chinese Spring genome.qRT-PCR showed that gene TraesCS5D016143300.1 encoding uridine-diphosphate glycosyltransferases(UGTs),gene TraesCS5D01G138700.1 encoding TIR-NBS-LRR proteins and gene TraesCS5D016141600.1 encoding heavy metal transport/detoxification superfamily proteins expressed differentially in the resistant variety ’04 Zhong 36’ and susceptible variety ’Xinmai 26’ after inoculation,which suggested that these genes may have vital roles in FCR resistance.3.For the first time,we investigated and compared the proteomic characteristics of two Chinese wheat varieties(’04 Zhong 36’ and ’Xinmai 26’)at 24 h,48 h,and 72 h post-inoculation using label-free quantitative proteomic analysis.There were 783 proteins differentially expressed after inoculation.Biological functions including ’aminoglycan catabolic’,’amino sugar catabolic’,’chitin metabolic’,’glucosamine-containing compound metabolic’,’cell wall macromolecule’ and ’metabolicglucosamine-containing compound catabolic’,were enriched in the resistant variety.Metabolic pathways including ’flavonoid biosynthesis’ and ’phenylpropanoid biosynthesis’ were also enriched.Thirty-three proteins associated with defense,cell wall formation,photosynthesis,etc.,showed consistently different expression between the resistant and susceptible genotypes at multiple time points.In particular,chitinase,which degrades chitin in the fungal cell wall and limits fungal growth,was exclusively and consistently upregulated in ’04 Zhong 36’ across the three time points.The partial resistant varieties in the study,such as ’04 Zhong 36’ and ’Shiyou 17’,enriched the resistant resources and laid foundation for future FCR related studies.The new SDL resistance QTL,which is not affected by plant height and heading date,plays an important role in FCR resistance at seedling stage and adult stage.Identification of candidate resistance genes for this region will provide valuable resources for molecular breeding and genetic improvement of FCR resistance.The differentially expressed proteins after FCR infection and their related coding genes can provide supplementary information for searching of candidate genes and studying the mechanism of FCR resistance.