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 F 1 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.Key Words: candidate gene, chromosome walking, polyploidy, proanthocyanidins.
IntroductionProanthocyanidins (PAs) are a class of final products of the flavonoid biosynthetic pathway that generally have protective roles against biotic and abiotic stresses. PAs are potentially attractive compounds in terms of human health because of their scavenging capacity for free radicals; PAs are also known to confer astringency or bitterness to fruit and vegetables (Aron and Kennedy, 2008;Bagchi et al., 2014;Dixon et al., 2005). The commercial and biological significance of PA biosynthesis has resulted in extensive studies being conducted on the PA biosynthetic pathway and its transcriptional regulators, especially in the model plant Arabidopsis thaliana (Lepiniec et al., 2006;Saito et al., 2013;Xu et al., 2015). Persimmon (Diospyros kaki Thunb.), an economically important fruit crop cultivated in temperate and Mediterranean climates, shows a distinctive characteristic of PA accumulation in its fruit. In persimmon fruit, the mean degree of polymerization of PA is high (approximately 10-40), and unlike other important fruit crops, persimmon fruit accumulates a vast amount of PA until the middle of fruit development, resulting in a This article is an Advance Online Publication of the authors' corrected proof. Note that minor changes may be made before final version publication. strong astringent taste even at commercial maturity (Akagi et al., 2009a(Akagi et al., , 2011. Depending on the genotype, persimmon fru...