| Sugar content is an important component of fruit quality.In this study,soluable sugars contents were mensurated using high performance liquid chromatography(HPLC)in mature fruits.The expression of MdSWEET genes in three stages of apple fruit development was detected by fluorescence quantitative PCR.Molecular markers(including SSR markers and CAPS molecular markers)were developed for relatively high expression genes.Finally,polyacrylamide gel electrophoresis(PAGE)was used to detect the polymorphisms of these markers.Although sugar transporters are known to be crucial for sugar accumulation,the role of genes encoding SWEET sugar transporters in fruit sugar accumulation remains elusive.Here,we report the effect of the SWEET genes on fruit sugar accumulation in apple.A total of 25 MdSWEET genes were identified in the apple genome,and nine were highly expressed throughout fruit development.Molecular markers of these nine MdSWEET genes were developed and used for genotyping of 188 apple cultivars.The association of polymorphic MdSWEET genes with soluble sugar content in mature fruit was analyzed.Three genes,MdSWEET2 e,MdSWEET9b and MdSWEET15 a,were significantly associated with fruit sugar content,with MdSWEET15 a and MdSWEET9 b accounting for a relatively large proportion of phenotypic variation in sugar content.Moreover,both MdSWEET9 b and MdSWEET15 a are located on chromosomal regions harboring QTLs for sugar content.Hence,MdSWEET9 b and MdSWEET15 a are likely candidates regulating fruit sugar accumulation in apple.Our study not only presents an efficient way of implementing gene functional study,but also provides molecular tools for genetic improvement of fruit quality in apple breeding programmes. |
