Genome-wide Association Mapping For Drought And Rewatering Related Traits At Seedling Stage In Brassica Napus L.

Rapeseed(Brassica napus L.)is an important oil crop,which is widely planted around the world.It is also one of the sources of edible vegetable oil in China.Drought stress is one of the major abiotic stresses that endanger agricultural production worldwide,seriously damaging the normal growth and development of rapeseed,as well as the yield and the quality of rapeseed.In recent years,there have been many researches on the B.napus L.under drought stress,mostly related to its physiological response mechanism and drought resistance mechanism.However,in the semi-arid area,the water environment of rapeseed growth is characterized by drought and short-term moistening.Hence,studying the growth status under drought and post-drought rewatering conditions to simulate the water characteristics of B.napus L.growth in semi-arid areas,which is of great importance for exploring the adaptability of B.napus L.during drought stress,including drought tolerance and comprehensive drought resistance after drought rehydration.In this study,a total of 120 diverse accessions,including cultivated species and inbred lines,were used to construct a research population.The shoot fresh weigh,root fresh weight,shoot dry weight,root dry weight,relative water content,leaf water retention and malondialdehyde content were determined in drought and well water,rewatering and well water.Using the Brassica 60 K single nucleotide polymorphism(SNP)array,32329 valid SNP locus were screened out,then we analyzed the population structure,relative kinship and linkage disequilibrium(LD)attenuation,and then genome-wide association analysis was performed on the drought resistance coefficient during drought stress and the comprehensive drought resistance after rewatering based on 6 models,indluding naive,Q,PCA,K,K+Q and K+PCA.Finally,candidate genes related to drought stress and rewatering were predicted by the candidate interval of the detected significant association SNP locus and the functional annotation of the homologous Arabidopsis genes.The main results were summarized as follows:1.Phenotypic analysis of drought and rewatering traits in B.napus L.:Drought stress reduced shoot fresh weigh,shoot dry weight,relative water content root fresh weight and root fresh weight,and increased leave water retention and MDA content.After rewatering,rapeseed seedlings had a certain degree of recovery2.Population structure and relative kinship analysis:120 accessions were divided into three subgroups(P1,P2 and P3),of which P1 subgroup included 40 accessions,accounting for 33.3%of all the accessions,P2 subgroup included 34 accessions,accounting for 28.1%of all the accessions,and the left were P3 subgroup.In the association panel,about 61%kinship between any two accessions were equal to 0,and about 20%kinship ranged from 0 to 0.1.3.Linkage disequilibrium analysis:The LD of both the A-subgenome and C-subgenome declined rapidly as the physical distance increased.But the extent of LD decay was different.The decay rate of the A-subgenome was faster than that of the C-subgenome.When the threshold value of r~2 was set to 0.2,the LD decay in the A-subgenome was about 250kb,and approximately 590kb in C-subgenome.4.Genome-wide association mapping:A total of 24 significant SNPs were screened for drought resistance coefficient,distributed in A02,A03,A04,A07,A08,A09,A10,C01,C03,C06chromosomes,which could explain about 17.65%to 34.43%of the phenotypic variation.Otherwise,a total of 256 significant SNPs were screened for comprehensive drought resistance,distributed in A01,A02,A03,A04,A05,A06,A07,A08,A09,A10,C01,C02,C03,C04,C05,C06,C07,C09chromosomes,which could explain the phenotypic variation rate of from 16.92%to 68.56%.T test was conducted on these detected SNPs,and finally 8 significant drought resistance coefficient-related SNP locus were screened for,which could explain about 20.65%to 27.55%of the phenotypic variation,and 96 significant comprehensive drought resistance-related SNP locus were obtained,which could explain about 16.92%to 45.93%of the phenotypic variation.5.Prediction of candidate genes:The LD region of all the detected significantly-related SNP locus were compared with French B.napus L.genome.Then genes were annotated according to the genome informations of Arabidopsis thaliana.Finally,25 genes were chosen to be candidate genes of drought resistance coefficient according to previous function annotation of genome,and 143genes were chosen to be candidate genes of comprehensive drought resistance according to previous function annotation of genome.Among them,the functions of genes included coding transcription factors,coding transport proteins,coding growth inhibitors,coding DNA/RNA binding proteins,coding enzymes,coding endogenous hormones,coding oxidative stress,osmotic stress,salt stress or water deprivation responsed proteins,responsing root system.The genes encoding enzymes were the most abundant.