Expression patterns of genes involved in sugar metabolism and accumulation during peach fruit development and ripening

In fleshy fruits, sugars (glucose, fructose, sucrose and sorbitol) are most important for fruit growth and development but also play a central role in fruit quality. In Peach (Prunus persica), we observed the sugars content at six developmental stages through high pressure liquid chromatography (HPLC). There was variation during fruit development and ripening, sucrose first increased then decreased; glucose and fructose first decreased, and then increased while sorbitol always decreased. In past, understanding about the mechanisms which control the sugar metabolism and accumulation in peach remains quite limited. We studied the transcript profiles of total 30 genes encoding key enzymes and transporters, which were involved in sucrose metabolism, resynthesis and transport. 13 putative genes including sucrose phosphatase synthase (PpSPS4 and PpSPS2), Hexokinases (PpHK1 and PpHK3), neutral/natural invertase (PpNIIVV1 and PpNINV2), vacuolar acid invertase (PpVAINV2), sucrose transporter (PpSUT2), vacuolar glucose transporters (PpVGT1, PpVGT2 and PpVGT3) and tonoplast mono-saccharides transporters (PpTMT1 and PpTMT2) highly expressed during peach fruit ripening. PpSPS4 had significantly positive correlation with glucose and fructose. Our results suggested that more sucrose accumulated in cytosol because of upregulation of (PpSPS4 and PpSPS2), that sucrose imported into vacuole through upregulation of PpSUT2, PpVGT1, PpVGT2, PpVGT3, PpTMT1 and PpTMT2 transporters, where cleaving of sucrose is done by upregulation of PpVAINV2. Hence, level of sucrose decreased as fruit ripe. As a result, the concentration of glucose and fructose increased at ripening stage (S4 II to S4 III). So, these marker genes can be involved in peach fruit ripening. This study will improve our understanding and lay foundation to explore the function of these genes and improvement of peach fruit quality.