Fruits of persimmon plants are traditional healthy food in China, Korea and Japan. However, due to the shortage of morphological and DNA markers, the development of persimmon industry has been heavily inhibited. Chloroplast genomes of Diospyros cathayensis, D. virginiana, D. rhombifolia and D. deyangensis were newly sequenced. Comparative analyses of ten chloroplast genomes including six previously published chloroplast genomes of Diospyros provided new insights into the genome sequence diversity and genomic resources of the genus. Eight hyper-variable regions, trnH-psbA, rps16-trnQ, rpoB-trnC, rps4-trnT-trnL, ndhF, ndhF-rpl32-trnL, ycf1a, and ycf1b, were discovered and can be used as chloroplast DNA markers at/above species levels. The complete chloroplast genome sequences provided the best resolution at inter-specific level in comparison with different chloroplast DNA sequence datasets. Diospyros oleifera, D. deyangensis, D. virginiana, D. glaucifolia, D. lotus and D. jinzaoshi are important wild species closely related to the cultivated persimmon D. kaki. The hyper-variable regions can be used as DNA markers for global genetic diversity detection of Diospyros. Deeper study on these taxa would be helpful for elucidating the origin of D. kaki.

Carotenoids in the peel and the flesh of persimmon fruit were identified, and the contents of carotenoids in the fleshes of 46 different persimmon cultivars were analyzed. The results indicated that 31 specific carotenoids were detected in both cultivars of persimmons, among which nine specific carotenoids were characterized. β-Cryptoxanthin was the most abundant carotenoid among all individual components in both the peel and the flesh, accounting for about 20-30% of the total carotenoids in both cultivars. The contents of total carotenoids in the fleshes of different persimmon cultivars were between 194.61 µg/100g FW and 1,566.30 µg/100g FW. Zeaxanthin was also the most abundant in all persimmon fleshes besides β-Cryptoxanthin, and the total amount of these two components accounted for 37.84-85.11% of the total carotenoids. The RE values in the fleshes of different cultivars also differed greatly. Besides, the stage of maturation was also important factor which could influence the carotenoid content and RE value in the fleshes.

The astringency of Chinese pollination-constant non-astringent (C-PCNA) persimmon (Diospyros kaki Thunb.) can be naturally removed on the tree. This process is controlled by a single locus and is dominant against other types of persimmons; therefore, this variant is an important candidate for commercial cultivation and the breeding of PCNA cultivars. In our previous study, six full-length coding sequences (CDS) for pyruvate kinase genes (DkPK1-6) were isolated, and DkPK1 is thought to be involved in the natural deastringency of C-PCNA persimmon fruit. Here, we characterize the eight other DkPK genes (DkPK7-14) from C-PCNA persimmon fruit based on transcriptome data. The transcript changes in DkPK7-14 genes and correlations with the proanthocyanidin (PA) content were investigated during different fruit development stages in C-PCNA, J-PCNA and non-PCNA persimmon; DkPK7 and DkPK8 exhibited up-regulation patterns during the last developmental stage in C-PCNA persimmon that was negatively correlated with the decrease in soluble PAs. Phylogenetic analysis and subcellular localization analysis revealed that DkPK7 and DkPK8 are cytosolic proteins. Notably, DkPK7 and DkPK8 were ubiquitously expressed in various persimmon organs and abundantly up-regulated in seeds. Furthermore, transient over-expression of DkPK7 and DkPK8 in persimmon leaves led to a significant decrease in the content of soluble PAs but a significant increase in the expression levels of the pyruvate decarboxylase (DkPDC) and alcohol dehydrogenase genes (DkADH), which are closely related to acetaldehyde metabolism. The accumulated acetaldehyde that results from the up-regulation of the DkPDC and DkADH genes can combine with soluble PAs to form insoluble PAs, resulting in the removal of astringency from persimmon fruit. Thus, we suggest that both DkPK7 and DkPK8 are likely to be involved in natural deastringency via the up-regulation of DkPDC and DkADH expression during the last developmental stage in C-PCNA persimmon.

Persimmon (Diospyros kaki) is the most economically cultivated species belonging to the genus Diospyros. However, little is known about the interspecific diversity and mechanism of domestication, partly due to the lack of genomic information that is available for closely related species of D. kaki (DK). Here, we performed transcriptome sequencing on nine samples, including DK, a variety of DK and seven closely related species, to evaluate the interspecific genetic divergence and to identify candidate genes involved in persimmon domestication. We obtained a total of 483,421 unigenes with N50 at 1490 bp in the nine Diospyros samples and identified 2603 orthogroups that were shared among all the samples using OrthoMCL analysis. A phylogenetic tree was established based on the tandem 2603 one-to-one single copy gene alignments, showing that DK was closely related to D. kaki var. silvestris (DKV) and that it clustered with the clade of D. deyangnsis (DD) and was farthest from the D. cathayensis (DC) species. The nonsynonymous substitutions (Ka), via synonymous substitution (Ks) ratios, was directly proportional to the genetic relationship of the different species. The higher the Ka/Ks ratios, the longer the distance was. Moreover, 31 positively selected genes (PSGs) involved in carbohydrate metabolism and phenolic metabolism were identified and isolated, and nearly all PSGs except the MATE gene had a high expression in the DK or DKV species. It was hypothesized that these genes might contribute to the domestication of the DK species. Finally, we developed the expressed sequence tag-simple sequence repeat (EST-SSR) and identified 2 unique amplicons DKSSR10 and DKSSR39: the former was absent in the DC species but was present in the other species, the latter had a long amplification product in the DJ species. This study presents the first transcriptome resources for the closely related species of persimmon and reveals interspecific genetic divergence. It is speculated that DK is derived from the hybridization of DD and DO species. Furthermore, our analysis suggests candidate PSGs that may be crucial for the adaptation, domestication, and speciation of persimmon relatives and suggests that DKSSR10 and DKSSSR39 could potentially serve as species-specific molecular markers.