Based on transcriptomics and untargeted metabolomics reveals the effects of urea-cytokinin on fruit development and quality of Shine Muscat.

In this paper, the effects of two urea cytokinins Forchlorfenuron(CPPU) and Thidiazuron (TDZ) and the combination of two plant growth regulators on grape fruit development and quality were studied, the dynamic changes of metabolites during ripening were analyzed, and the mechanism of different cytokinins and their combinations promoting grape fruit expansion and affecting fruit flavor was clarified. The results showed that: (1) different urea cytokinins and their combinations effectively increased single fruit weight, and the fruit shape index of TDZ treatment was different from that of other treatments. CPPU treatment increased total sugar content and decreased total soluble solids and organic acids content, while TDZ and CPPU+TDZ increased total soluble solids and total sugars content and decreased organic acids content. (2) The types and relative contents of aroma compounds produced by different treatment groups were different. Compared with CK, CPPU+TDZ increases the types of terpenes, aldehydes and esters. The relative contents of esters and terpenes in the treatments were increased. The relative content of aldehydes increased in CPPU and CPPU+TDZ treatment. (3) Transcriptome data analysis showed that TCH4 was involved in the regulation of fruit expansion, and LOXC, ADH1-2 and PAL were involved in the synthesis of fruit aroma compounds. (4) Combined Transcriptome and Non-targeted Metabolomics analysis showed that aroma compounds were synthesized mainly in fatty acid pathway, amino acid pathway, secondary metabolites and carbohydrates. In summary, the application of urea-cytokinin has different effects on grape quality and flavor, and different treatment methods should be selected according to different market demands in actual production, in order to obtain market satisfaction and higher returns. This study revealed the influence mechanism of exogenous urea cytokinins on grape fruit expansion and aroma compound synthesis, and provided a theoretical basis for reasonable application of cytokinins in practical production.