Comparative Genomics of the Locus Controlling Astringency in Diospyros species

Persimmon (Diospyros kaki ; 2n = 6x = 90) accumulates a large amount of proanthocyanidin (PA) in its fruit, resulting in an astringent taste. Persimmon cultivars are classified into four types based on the nature of the astringency loss and the amount of PA remaining in the mature fruit. Pollination-constant and non-astringent (PCNA) type cultivars stop accumulating PA early in fruit development and can be consumed when still firm without the need for artificial deastringency treatment. It has been shown that the PCNA trait is conferred by a recessive allele at a single locus (ASTRINGENCY ; AST). The exact genetic determinant remains unidentified, partly because of the complex segregation in hexaploid D. kaki. In this study, we used D. lotus (2n = 2x = 30), one of the closest relative of D. kaki, as a reference to characterize the AST locus. Using BAC sequencing, we obtained a 850-kb D. lotus genomic contig, which is syntenic to the D. kaki genomic region that includes the AST locus. We performed comparative mapping analysis using an F1 population of 296 D. kaki sibling trees segregating for the astringency trait and another F1 population of 336 D. lotus sibling trees. DNA markers developed from the 850-kb region of D. lotus genomic sequence were used for genetic analysis in D. kaki. Although the astringency phenotype and marker genotypes were consistent with each other in all D. kaki individuals tested, we did identify individuals with recombination events falling within the genome region syntenic to the D. lotus 850-kb region. The average physical distance relative to the genetic distance in this region was approximately 220 kb/cM in D. lotus, suggesting that the AST locus is probably located in a euchromatic region. Collectively, comparative genomics appear to be a promising approach to identify the gene(s) responsible for astringency in persimmon.