Evaluation,QTL Analysis And Candidate Gene Prediction For Berry Texture In Vitis Vinifera L.

Berry texture is an important indicator of grape taste.It is also one of the most important target traits in grape breeding globally.Therefore,identification of the molecular mechanisms of the formation of grape berry texture will provide important bases for the development of high quality grape breeding and production.In addition,with the advancement of molecular marker technology,the identification of molecular markers closely linked to berry texture and its application in early selection will greatly shorten the breeding cycle.In this study,we evaluated the texture traits of a large number of grape germplasms using TPA method and studied their texture changes during berry development.We also studied the mechanisms of the effect of gibberellin in regulating berry texture by proteomic analyses,and constructed a high density map of the grape germplasms.Based upon the above analyses we constructed the QTL map of the firmness characteristics of grape pulp texture and determined several candidate genes related to it.The main results are as follows:?1?The TPA method was used to identify and evaluate the texture of 290 grape varieties of different usage types.On the whole,the fruit texture of table grape is higher,while that of wine grape and juice grape is lower;the texture of the Vitis vinifera is higher,while that of the Vitis vinifera×Vitis labrusca hybrid is lower.This may be related to the genetic basis of different germplasms and the relevant manual selection.By analyzing the TPA parameters of different grape germplasms,it was found that the following pairs of factors were significantly positively correlated:firmness and chewability,elasticity and cohesion,elasticity and recovery,cohesion and recovery,and chewability and recovery.Principal component analysis showed that the contribution rate of the first two principal components to the texture of grape pulp reached 95.79%.The elasticity and firmness had a great influence on the texture of pulp,which could be used as an important parameter to determine the texture of grape pulp.?2?By comparing the texture changes of two different grape varieties,'Muscat hamburg' and 'Crimson seedless',during berry development,it was shown that the berry firmness of the soft flesh variety 'Muscat Hamburg' has decreased significantly during the entire berry development period.The firmness of the soft-fleshed variety decreased sharply before the verison period,while the hard-fleshed variety occurred only after the verison period.During the berry development,the content of protopectin showed a downward trend during the berry development and the soft-fleshed variety declined more significantly.The soluble pectin content of the soft-fleshed variety was higher than that of the hard-fleshed variety,while the cellulose content was just the opposite;the PG enzyme activity and the gene expression level are basically consistent with the decline of berry firmness,indicating that PG plays an important role in grape berry texture changes.?3?Gibberellin was shown to be able to increase the single fruit weight of 'Summer Black',and slightly decrease the soluble solid content of the fruit,which significantly improved the firmness and chewability of the fruit with no obvious effect on its the elasticity,cohesiveness and recovery.Differential proteomic analysis was performed for the gibberellin-treated?50 mg/L?sample and the control 90 days after flowering.The firmness of the flesh texture between the two was significantly different.Quantitative analysis by iTRAQ identified a total of 788 differentially expressed proteins.There were 246 proteins up-regulated and 542 proteins down-regulated.Enrichment analysis was used for these differentially expressed proteins in the KEGG metabolic pathway.These differentially expressed proteins were mainly enriched in galactose metabolism pathways,metabolic pathways,pentose and glucuronide interaction pathways,and secondary metabolite synthesis,including ?-galactosidase,pectin methyl esterase PME1 precursor,?-glucosidase,pectin esterase,pectinlyase,polygalacturonase,calcium-binding protein,galactosyltransferase,etc.It is predicted that these proteins are involved in the regulation of fruit texture.?4?A genetic population map was constructed using the F1 generation of 105 true crosses of 'Muscat hamburg' × 'Crimson seedless'.HiSeq 4000 sequencing platform was used to resequence the parent and offspring samples,and the original data was filtered and screened to obtain effective data of 790.63 G.Q30 ratio was between 91.96%-94.05%.GC content ratio was between 36.20%-38.37%.The molecular genetic maps of 'Muscat Hamburg' and 'Crimson Seedless' were successfully constructed.The integrated genetic map is composed of 19 linkage groups,including 1622 Bin markers?26039 SNPs?,covering a total map distance of 1460.38 cM and an average distance of 0.88 cM between markers.It is one of the high genetic density grape maps and can be used as a follow-up basis of quantitative trait QTL mapping.?5?Analysis of the firmness characteristics of the flesh texture of the parents and their F1 population for 3 consecutive years showed that there were significant differences in the firmness of the flesh texture between the parents,and there was a continuous variation in the F1 population.Its distribution was close to the normal distribution.By using the integrated genetic mapping,combined with three years of phenotypic data,and by using composite interval mapping,a total of three berry firmness-related QTL loci were detected:all of which were distributed on the 18th linkage group,with single QTL locus contribution ranging from 21.5%-28.6%.By screening the genetic map,4 candidate genes related to the texture of grape pulp were detected.These genes were mainly related to endoglucan,abscisic acid,NAC transcription factor and MADS-box transcription factor.Further qRT-PCR analysis showed that the expression levels of VIT₁8s0041g02410 and VIT₁8s0089g00210 in different fruit development stages of 'Crimson seedless' and'Muscat hamburg' were basically consistent with the decline in the berry firmness.Therefore it suggested that VIT₁8s0041g02410 and VIT₁8s0089g00210 are the candidate gene locus associated with berry firmness.