Transcriptome and Metabolome Combined Analysis Reveals Key Genes Controlling Soluble Sugar Metabolism in Persimmon Fruit During Development

Persimmon as a type of fruit is divided into pollination-constant and non-astringent (PCNA) persimmon, which can lose its astringency naturally during fruit ripening, and non-PCNA persimmon. Its soluble sugars include the essential components that determine the flavor of the persimmon fruit. However, the underlying regulatory networks that modulate the metabolism of soluble sugar in persimmon fruit remain largely unknown. In this work, three stages (10, 15, and 20 weeks after bloom) of Chinese PCNA 'Luotian tianshi' fruit growth were used as experimental models to reveal the molecular mechanism of soluble sugar metabolism via the combination of the transcriptome and the metabolome. Here, 21 kinds of soluble sugars were detected, with sucrose, glucose, and fructose verified as the main soluble sugars in the persimmon fruits. We obtained 59.42 Gb of clean data via transcriptome sequencing, and the maximum number of differentially expressed genes (9098) was found in the 20 W vs. 10 W groups, of which 2513 were up-regulated and 3811 were down-regulated. The KEGG enrichment analysis showed that 37 up-regulated and 71 down-regulated differentially expressed genes were enriched for starch and sucrose metabolism in the 20 W vs. 10 W groups. The metabolome and transcriptome association analysis showed that the differentially expressed genes (malZ, INV, SPS, scrK, ISA, beta-AMY, TPS, otsB, and TREH) were significantly correlated with the content of differentially accumulated metabolites (such as sucrose, glucose, and fructose), indicating that they may play important roles in the metabolism of the soluble sugars in persimmon. Overall, this study provides valuable insights into the metabolism pattern of high sugar accumulation in persimmon fruit.