Germplasm Screening And Genetic Mechanism Analysis Of Submergence Tolerance During Rapeseed Germination

Rapeseed is the first oil crop in China.The flooding stress caused by the frequent rainfall in the basin of the Yangtze River severely affects the emergence and germination of the germination period.Therefore,the analysis of the genetic and molecular mechanisms of submergence tolerance in the germination period of rapeseed is important for the breeding of submerge-resistant varieties.The main purpose of this study was to screen 505 inbred lines of Brassica napus germplasm resources and obtain germplasm resources with strong submerge resistance during the germination period.Second,to measure the physiological parameters after submerging treatment.And dissect the genetic mechanism of submergence tolerance by identify the correlated significant variation sites related to submerge-resistant.Third,to choose two representative materials with extreme submerging tolerance for transcriptome analysis and identify the differentially expressed genes as well as the biological processes in which these genes are mainly enriched.Gene expression will be used to predict candidate genes in QTL interval.The most highlighted significance of this study is to screen the germplasm resources with strong submerge resistance and to reveal the genetic and molecular mechanisms of submergence resistance in the germination period of rapeseed.The main results are as follows:The phenotypes and physiological indexes of 505 inbred rapeseed germplasms were measured at the germination stage.The measurement items included unit electricity conductivity,relative electricity conductivity,root length,stem length,root fresh weight,root dry weight,stem fresh weight,stem dry weight,total fresh weight,total dry weight and total length.The results indicated that there was a significant correlation between unit electricity conductivity and relative electricity conductivity.Nine phenotypic traits were significantly affected under the submerging stress,in which the roots were affected most;four submerge-resistant materials and eight sensitive materials were identified by physiological and phenotypic indicators.Besides,we also found that the tolerance coefficient of phenotypic traits was negatively correlated with oil content and positively correlated with 1000-seed weight.Based on 505 re-sequencing data of rapeseed,Genome-wide association analysis(GWAS)of phenotypic traits and physiological indicators was performed using a mixed linear model.We identified 78 significantly associated SNP of flooding tolerance(-log(P)>7.0).Among which,five significant sites were related to root length,eight significant sites were related to stem length,two significant sites were related to the root fresh weight,and five significant sites were related to the root dry weight,four significant sites were related to stem dry weight,six significant sites were associated with stem fresh weight and seven significant sites were related to membership function evaluate waterlodding(MFVW).This study identified 2 extreme varieties(76 and 180)for transcriptome analysis based on physiological and phenotypic indicators.The results showed that 4767 differentially expressed genes were obtained by comparing submerge-resistant materials(76)after 6 hours of treatment with control.There were 7150 differentially expressed genes were obtained from sensitive materials(180)after 6 h immersion treatment compared to the materials without immersion treatment.There were 14226 differentially expressed genes obtained by comparing submerge-resistant materials(76)with sensitive materials(180)before immersion treatment.There were 10803 differentially expressed genes obtained by comparing submerge-resistant materials(76)with the sensitive materials(180)after 6h immersion treatment.A total of 12963 genes showed down-regulated expressions and 10834 genes were up-regulated.In this study,all the differentially expressed genes were compared with the genes in the candidate intervals for association analysis.A total of 79 differentially expressed genes were overlapped with the genes identified near the significant site.Four submerge-resistant materials and eight sensitive materials were identified by phenotypic and physiological indicators in this study.Two representative materials with extreme tolerance were selected for RNA-seq,and a total of 79 differentially expressed candidate genes were identified by transcriptome analysis combined with candidate intervals for association analysis.Among them,40 differential genes were identified as candidate genes.These candidate genes laid the foundation for the study of mechanisms of submergence tolerance of rapeseed.