Fine Mapping Of QTL For Cucumber Pulp Thickness And Functional Verification Of Candidate Genes

Cucumber(Cucumis sativus L.)is one of the most important vegetable crop in the world,and generally taken as the annual vine genus of in Cucumis of Cucurbitaceae.With the improvement of people’s living standard,the requirement for the quality of cucumber is increasing day by day.The flesh thickness is an important texture quality of cucumber,which is closely related to the accumulation of dry matter.So it is important to isolate and identify the flesh thickness gene,improve the germplasm by means of modern molecular biological technology,and improve the cucumber texture quality.This study took advantage of F2 population,which was constructed of the D8(thick flesh parent)and XUE1(thin flesh parent)for the phenotypic data investigation and statistics,then in F2 group pick 50 strains of thick flesh plant to compose thick flesh pool,50 strains of thin flesh plant to compose thin flesh pool,with high throughput sequencing method of Cucumber thick flesh pool and thin flesh pool was simplified genome sequencing(SLAF-seq);analyse the relative expression quantity of genes between the QTL region with the use of qRT-PCR and verify the candidate genes’ function in two parents(D8 and XUE1).The main results were as follows:1.The thickness of the flesh of each individual plant in F2 population was statistically normal distribution,which showed that the thickness of the flesh was a quantitative trait.2.Using the SLAF-seq method to develop a total of 100535 SLAF tags,the average depth of the parent SLAF tag was 20.1 OX,the average depth of the mixed pool was 44.60X.In view of these tags,according to the difference between the number of alleles and gene sequence polymorphism analysis,8232 polymorphic SLAF tags were obtained,screen the obtained 8232 polymorphic SLAF tags according to the SNP marker sequencing depth and parental genotype,2259 were selected for correlation analysis.3.The correlation analysis was performed by using the SNP index method of 2259 candidate polymorphic SLAF tags,and the fitting correlation threshold was 0.1307,and 23 SLAF tags,which were significantly correlated with the traits,were obtained,navigating to a related area by selecting 0.1307 as threshold on the same chromosome polymorphism SLAF labels’△(SNP_index),located between the chromosome 2 4412753～4604081 and size for 0.19Mb.4.By comparing with the reference genome of cucumber,there are 20 genes in the QTL region.In the 20 genes,Csa2G058670’S expression results and two parents flesh thickness’correlation analysis are significant,which contains SET conserved domain of protein and used for phylogenetic tree analysis with the Arabidopsis SET gene family.The gene and gene At2g18850 have high homology and At2g18850 is related with plant cell division and growth.5.Using qRT-PCR to analyse Csa2G058670 in two parent fruit different development time and finding the gene in the two species relatively express different,the relative expression of the same time in the flesh were higher than in peel,increased significantly from Od to 9d in D8 and in XUE1 the expression was relative high at Od then decline,speculated that the expression of the gene in the two species belong to the two different patterns of expression.6.Cloning gene Csa2G058670 in eight different fruit flesh varieties.Taking advantage of sequence analysis software,we found that the cloning sequence from four thin fruit flesh varieties have 4-bp deletion at the start of the promoter region.It was also found that the thin fruit flesh varieties have two base mutations in the coding region of the coding exon region.These results further illustrate gene Csa2G058670 was closely related to the development of cucumber fruit flesh thickness.