Sex Determination in Oriental Persimmon (Diospyros kaki)

Separate sex, which is represented by dioecy, monoecy, or their variants, is one of the main strategies of flowering plants to maintain genetic diversity within a species. At the same time, sexuality is an important trait affecting crop production and breeding efficiency. Recently, a Y-chromosome-encoded gene, designated Oppressor of MeGI (OGI), has been shown to play a central role in sex determination in dioecious diploid persimmons (Diospyros spp.). However, little is known about the potential role of OGI in the irregular polygamous sexuality in polyploid oriental persimmon (D. kaki). D. kaki, which is mostly hexaploid, with some nonaploid individuals, is mainly constituted of monoecious and female individuals. Among 172 cultivars tested in this study, the OGI sequence was found in all 35 monoecious individuals producing male flowers, which suggested a conserved role for OGI as a key to expressing maleness in D. kaki, as in dioecious diploid Diospyros. In D. kaki, however, the presence of OGI does not always lead to male flower formation and expression of OGI is silenced. Developing male buds consistently exhibited higher methylation across the MeGI promoter than developing female buds from either monoecious or female trees. This could indicate that an additional layer of regulation, methylation of the MeGI promoter, may be necessary to produce both male and female flowers on genetically male trees. Consistent with this hypothesis, a DNA methylation inhibitor could reverse male developing buds to form feminized flowers.