Comparative mapping of the ASTRINGENCY locus controlling fruit astringency in hexaploid persimmon (Diospyros kaki thunb.) with the diploid D. lotus reference genome

Persimmon (Diospyros kaki) is a tree crop species that originated in East Asia, consists mainly of hexaploid individuals (2n = 6x = 90) with some nonaploid individuals. One of the unique characteristics of persimmon is the continuous accumulation of proanthocyanidins (PAs) in its fruit until the middle of fruit development, resulting in a strong astringent taste even at commercial fruit maturity. Among persimmon cultivars, pollination-constant and non-astringent (PCNA) types cease PA accumulation in early fruit development and become non-astringent at commercial maturity. PCNA is an allelic trait to non-PCNA and is controlled by a single locus called the ASTRINGENCY (AST) locus. Previous segregation analyses indicated that the AST locus shows hexasomic inheritance; a recessive allele, ast, at this locus confers PCNA. Here, we report a shuttle mapping approach to delimit the AST locus region in the hexaploid persimmon genome by using D. lotus, a diploid relative of D. kaki, as a reference. A D. lotus F₁ population of 333 individuals and 296 D. kaki siblings segregating for the PCNA trait were used to map the AST region using haplotype-specific markers covering the AST region. This indicated that the AST locus is syntenic to an approximately 915-kb region of the D. lotus genome. In this 915-kb region, we found several candidates for AST that were revealed from the fruit transcriptome of a population segregating for the PCNA trait. These results could provide important clues for the isolation of AST in hexaploid persimmon.