Advance on deastringency mechanism in Chinese PCNA persimmon

Persimmon fruits accumulate high amount of proanthocyanidins (PAs, condensed tannin) derived from flavan-3-ols units. Rapid progress on persimmon PAs biosynthesis pathway had been made by genomics, transcriptomics, proteomics, and metabolism. This review focus on characteristics of the tannin cells and latest research progress on key genes or transcription factors and their regulatory mechanisms related to PAs metabolism especially on natural deastringency process in C-PCNA (Chinese pollination constant & non-astringent) persimmon. There are distinct genetic backgrounds between C-PCNA and J-PCNA (Japanese pollination constant & non-astringent) based on some molecular markers detection and F₁ astringency segregations. The fruit tannin cells area in non-PCNA cultivars is remarkably larger than that in J-PCNA and C-PCNA. Large tannin molecules exist in C-PCNA fruits like non-PCNA but not in J-PCNA. PAs biosynthesis continued to the fruit late developmental stages in C-PCNA persimmon. Dilution of tannins accounts for natural astringency-loss in J-PCNA persimmons. Except dilution of tannins, natural astringency-loss of C-PCNA persimmon is probably related with the soluble tannin coagulation occurence since 25 weeks after bloom. A dominant allele CPCNA is suggested to control C-PCNA natural deastringency against non-PCNA. RO2 marker strongly linked to the CPCNA was developed and helpful for C-PCNA breeding. Pyruvate decarboxylase (PDC) and alcohol dehydrogenase (ADH) involved in tannins coagulation leading to natural deastringency in C-PCNA. Pyruvate kinase genes DkPK1 (regulated by DkWRKY3 and DkWRKY15), DkPK7 and DkPK8 are likely to be mediated in natural deastringency via the upregulation of DkPDC and DkADH expression during late developmental stage of C-PCNA persimmon fruit. Aldehyde dehydrogenase genes DkALDH2a and DkALDH2b are negatively correlated with natural deastringency in C-PCNA. Transcription factor DkMYB14 was characterized to be a key regulator as both a transcriptional activator and a repressor through directly repressing biosynthesis of PAs and promoting its insolubilization. A microRNA143 might also promote soluble tannin coagulation through inhibition of DkALDH10 expression in C-PCNA. Obviously, analysis of soluble tannin and insoluble tannin composition and the process of PAs monomers transport and polymerization are clearly required. This review provides a new insight on elucidating mechanism on natural deastringency process in Chinese PCNA persimmon and approach for genetic improvement.