Recent Advances in Natural Deastringency and Genetic Improvement of Chinese PCNA Persimmon (Diospyros kaki)

Persimmon (Diospyros kaki) is a worldwide fruit cultivated mainly in the East Asia, Mediterranean, Caucasus, Latin America, and Oceania regions. This fruit contains abundant proanthocyanidins (PAs, also called condensed tannins), whose biosynthesis is the main cause of fruit astringency. As the original centre and top producing country, China has discovered a unique type with desirable natural deastringency, the Chinese pollination-constant non-astringent (C-PCNA) persimmon. Studies have revealed that the C-PCNA trait is controlled by a single and dominant locus, which differs from that of another type, the Japanese PCNA type, with recessive loci. In the C-PCNA type, accumulating evidence has shown that the astringency removal process involves two pathways ("dilution effect" and "coagulation effect"). Moreover, molecular marker-assisted selection (MAS) for the natural deastringency trait locus in C-PCNA has been used to test the non-astringency/astringency trait of hybrid offspring at the seedling stage. Importantly, persimmon can bear male flowers, female flowers, and perfect flowers, but sex-linked MAS has been developed for female-only persimmon. This sex-linked MAS, together with astringency-linked MAS and embryo rescue technology, may even shorten the conventional cross-breeding period of about 2-3 years. In addition, recently studies have established a stable genetic transformation system for persimmon transgenic improvement. Despite these efforts, how synthetic PAs and metabolism pathways lead to a deastringent trait remains unclear for persimmon. Thus, our review summarizes the latest research progress on the natural deastringency mechanism in C-PCNA, and we provide a new viewpoint for the genetic improvement of persimmon breeding in China.