Persimmon (Diospyros kaki) fruit have significant variation between pollination-constant non-astringent (PCNA) and pollination-constant astringent (PCA) persimmons. The astringency type affects not only the soluble tannin concentration but also the accumulation of individual sugars. Thus, we comprehensively investigate the gene expression and metabolite profiles of individual sugars to resolve the formation of flavor differences in PCNA and PCA persimmon fruit. The results showed that soluble sugar, starch content, sucrose synthase, and sucrose invertase were significantly different between PCNA and PCA persimmon fruit. The sucrose and starch metabolism pathway was considerably enriched, and six sugar metabolites involving this pathway were significantly differentially accumulated. In addition, the expression patterns of diferentially expressed genes (such as bglX, eglC, Cel, TPS, SUS, and TREH genes) were significantly correlated with the content of deferentially accumulated metabolites (such as starch, sucrose, and trehalose) in the sucrose and starch metabolism pathway. These results indicated that the sucrose and starch metabolism pathway maintained a central position of sugar metabolism between PCNA and PCA persimmon fruit. Our results provide a theoretical basis for exploring functional genes related to sugar metabolism and provide useful resources for future studies on the flavor differences between PCNA and PCA persimmon fruit.

Persimmon (Diospyros kaki Thunb.) is an economically important tree with a long history of cultivation in China. So far, a total of approximately 1000 varieties have been found in China. To systematically evaluate the diversity of persimmon fruit quality, 22 quality measures of appearance, intrinsic, and sensory quality were evaluated using 61 typical persimmon fruit. According to the findings, the coefficient of variation (CV) of 15 appearance and intrinsic quality index values ranged from 13.81% (fruit shape index) to 165.80% (firmness), and the CV values of 7 intrinsic quality attributes were all higher than 50%, with the CV of total polyphenols and ironic soluble pectin contents (ISP) being as high as 159.82% and 143.80%, respectively. These findings showed that several persimmon germplasm resources had a highly diverse range of fruit quality, wide variation, and distribution. Insoluble tannin and soluble sugar were shown to have a substantial positive correlation with the sensory flavor indexes (p < 0.05), indicating their significance in influencing the flavor quality of persimmon fruit. Cluster analysis was performed utilizing 15 indexes of appearance, intrinsic quality, and 7 indexes of sensory quality. The samples were divided into two groups: group I consisted of 52 pollination−constant and astringent (PCA) and 1 pollination−-variant astringent (PVA) persimmon resources, and group II consisted of 6 pollination−constant non−astringent (PCNA) and 2 pollination−variant non−astringent (PVNA) persimmon resources. The results were consistent with the classification based on the mode of astringency loss, indicating that there was a significant difference in the quality of astringent and non−astringent persimmon fruit. This study provides theoretical references for the development and application of persimmon germplasm resources.

To explore the mechanisms of the color formation of different colored persimmon fruits, we used two different colored persimmon cultivars (yellow-peeled persimmon fruit ‘Zhongshi No.6’ and red-peeled persimmon fruit ‘Hongdenglong’) as materials to study the synthesis and accumulation of carotenoids in three stages (full green, color transition, and full yellow or red) using targeted metabolomic and transcriptomic methods. A total of 14 carotenoids and 30 carotenoid lipids were identified in the peel of the two persimmon cultivars. After analysis, it was found that the total carotenoid content of the red persimmon cultivar was higher than that of the yellow persimmon cultivar. The contents of lycopene, α-carotenoid, β-carotenoid, (E/Z)-phytoene, and β-cryptoxanthin are the main reasons for the difference in total carotenoid content between the two persimmon cultivars, especially lycopene. Twelve structural genes involved in the metabolism of carotenoids were also found in this study. In comprehensive metabolome and transcriptome analysis, we found that, between the two persimmon cultivars, lycopene was the key metabolite responsible for the color difference, and PSY, LCYE, and ZDS were the key genes that regulated the differences in lycopene accumulation. The results of this study provide us with new information regarding persimmon fruit synthesis and accumulation. In addition, they also provide a theoretical foundation for improving persimmon fruit germplasm.

Basic helix–loop–helix (bHLH) proteins belong to one of the largest families involved in plant growth, development, signal transduction, and secondary metabolism. Although bHLH genes have been previously identified in persimmon (Diospyros kaki), systematic studies have not been reported. A total of 59 bHLH family members have been identified from the “Xiaoguotianshi” persimmon transcriptome. These proteins were clustered into 12 groups from I to XII based on their phylogenetic relationships with Arabidopsis thaliana. Combined with the phylogenetic analysis, in silico expression patterns of five developmental stages, the protein–protein interaction analysis between DkbHLH and DkMYB proteins showed that the bHLH_Cluster-15548.1 protein sequence was identified to be highly similar to the AtGL3 (AT5G41315.1) protein, which is associated with flavonoid and proanthocyanidin (PA) biosynthesis. This study presents the systematic analysis of bHLH genes from D. kaki and provides valuable information for further research on the involvement of bHLH protein in anthocyanin biosynthesis.

Most varieties of persimmon (Diospyros kaki Thunb.) are gynoecious, while just a few are either monoecious, androgynomonoecious, or androecious. Persimmon flowers initially contain the original androecium and gynoecium followed by arrest of either pistil or stamen primordia before maturity. Abortion of inappropriate primordium in persimmon may be related to programmed cell death (PCD). To test this hypothesis, hematoxylin and eosin (H&E) staining, terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) assay, cyt-c immunohistochemistry (IHC) assay, transmission electron microscopy (TEM) observation, and real-time quantitative polymerase chain reaction (RT-qPCR) were used to clarify the occurrence and molecular regulatory mechanism of PCD in male and female floral buds during the 14 days prior to the second crucial morphological stage when inappropriate sexual primordia were arrested to form unisexual flowers. Accordingly, dead cells in inappropriate sex organs were largely accumulated during the microsporocyte and macrosporocyte period of male and female floral buds, respectively. This may explain the abortion of inappropriate sex organs, leading to unisexual flowers. PCD is necessary for normal growth and development in persimmons, as dead cells could also be observed in the normal flower organs. High levels of a gene homologous to AMC9 may have accelerated the arrest of the pistil primordium during differentiation, leading to male unisexual flowers, and high levels of genes homologous to MeGI, BAG5, AifA, and HSP70 in female floral buds were positively correlated with the arrest of stamen primordium. Future studies may try to transform unisexual flowers into hermaphroditic flowers by the regulation of PCD artificially, which will be helpful to the controlled pollination experiments.

Fruit shape is an important external feature when consumers choose their preferred fruit varieties. Studying persimmon (Diospyros kaki Thunb.) fruit shape is beneficial to increasing its commodity value. However, research on persimmon fruit shape is still in the initial stage. In this study, the mechanism of fruit shape formation was studied by cytological observations, phytohormone assays, and transcriptome analysis using the long fruit and flat fruit produced by ‘Yaoxianwuhua’ hermaphroditic flowers. The results showed that stage 2–3 (June 11–June 25) was the critical period for persimmon fruit shape formation. Persimmon fruit shape is determined by cell number in the transverse direction and cell length in the longitudinal direction. High IAA, GA₄, ZT, and BR levels may promote long fruit formation by promoting cell elongation in the longitudinal direction, and high GA₃ and ABA levels may be more conducive to flat fruit formation by increasing the cell number in the transverse direction and inhibiting cell elongation in the longitudinal direction, respectively. Thirty-two DEGs related to phytohormone biosynthesis and signaling pathways and nine DEGs related to cell division and cell expansion may be involved in the persimmon fruit shape formation process. These results provide valuable information for regulatory mechanism research on persimmon fruit formation.