A comprehensive transcriptomic and metabolomic map reveals the molecular mechanism of persimmon fruit deastringency upon 40 °C warm water treatment

Persimmon (Diospyros kaki Thunb.) is a widely cultivated fruit crop. Predominantly, its pollination-constant astringent (PCA) cultivars that accumulate proanthocyanidins (PAs) during maturation, resulting in an astringent taste. In this study, twenty PCA-type cultivars were subjected to warm water treatment at five time points (0, 8, 16, 24, and 32 h). It revealed that astringency removal can be achieved in 19 cultivars, and 11 varies complete astringency removal within 16 h. To elucidate the underlying mechanism of deastringency, the cultivar of ‘Zheng 20’ persimmon fruit treated with 40 °C water was investigated, using a combined metabolomics and transcriptomics approach. A total of 48,937 high-quality unigenes were obtained through full-length RNA sequencing and functional annotation. Subsequently, transcriptome and metabolomic changes in persimmon fruit in response to warm water deastringency were analysis. Pathways associated with acetaldehyde metabolism, pectin synthesis and PA synthesis were identified. An interaction was observed between DkbZIP17 and DkWRKY3, which showed up-regulated gene expression in persimmon treated with warm water. Additionally, the overexpression of the DkbZIP17 and DkWRKY3 genes could promote soluble PA coagulation, and upregulate the acetaldehyde-related DkADH, DkPDC and DkPK genes in ‘Mopanshi’ persimmon leaves in vivo. Interestingly, simultaneous expression of DkbZIP17 and DkWRKY3 in persimmon leaves produced a synergistic effect that was more effective than the overexpression of a single gene. Overall, our results suggest that the DkbZIP17 and DkWRKY3 genes are involved in deastringency in persimmon fruit treated by 40 °C water via enhancement of acetaldehyde metabolism.