Development of Molecular Markers Associated with Sexuality in Diospyros lotus L. and Their Application in D. kaki Thunb.

Abstract

Sexuality of crops affects both cultivation and breeding systems. Cultivated persimmon (Diospyros kaki Thunb) has a morphologically well-characterized polygamous or gyonodioecious sexual system. However, the genetic basis of sexuality in D. kaki has yet to be characterized. Here, we used dioecious D. lotus L., a diploid wild relative species to hexaploid or nonaploid D. kaki, as a model to clarify the genetic basis of sexuality in Diospyros and to develop molecular markers associated with the sexuality of individuals. Using 62 F1 offspring segregated into distinct male/female phenotypes, we found two amplified fragment-length polymorphism markers, DlSx-AF4 and DlSx-AF7, which cosegregated with maleness. This could suggest that the sexuality of D. lotus is controlled by a single gene/haploblock, and the male is dominant over the female. Thus, D. lotus’s sexuality can be described as the heterogametic male type, the XY-type, as reported for most other dioecious plant species. For unknown reasons, segregation of the phenotype of a sequence-characterized amplified region marker developed from DlSx-AF4 (DlSx-AF4S) and/or the male/female phenotype in two different crosses in D. lotus showed an apparent bias towards femaleness and better fitted 1:2 than 1:1, which is the theoretical segregation for a single genetic locus or haploblock in diploid D. lotus. DlSx-AF4S could distinguish D. kaki cultivars with female and male flowers from cultivars with only female flowers, strongly indicating that the same genetic system controls D. kaki’s sexuality and that DlSx-AF4S could be used as a genetic marker for sexuality in D. kaki breeding programs.

雌雄性は作物の栽培そして育種の大きな制限要因となる．カキ（Diospyros kaki Thunb.）の雌雄性に関してこれまでに多くの形態学的な観察が行われ，カキは雌雄混株あるいは雌性両性異株とされている．しかしながら，カキにおける雌雄性の遺伝制御機構は明らかにされていない．本研究では，カキ（六倍体あるいは九倍体）の近縁野生種であり，雌雄異株であるマメガキ（D. lotus L.）（二倍体）を用い，交雑分離集団を作出し，雌雄分離の調査を行った．また同じ集団を用いて AFLP 解析によって雌雄性判別のための分子マーカーの開発を試みたところ，雄性と共分離を示す 2 種類の AFLP バンド（DlSx-AF4 および DlSx-AF7）が同定された．このため，マメガキの雌雄性は，他の多くの雌雄異株の植物種と同じく，単一の遺伝子座（ハプロブロック）によって支配される雄性異型接合型（XY 型）であることが明らかになった．しかし，DlSx-AF4 から作製した SCAR マーカー DlSx-AF4S および雌雄性形質の分離は，一遺伝子座支配における理論値である 1:1 から有意に雌性側に偏り，1:2 に近い分離を示した．DlSx-AF4S はカキにおいても雄花の着花性と相関を示し，カキの雌雄性もマメガキと同様の遺伝制御を受けていること，ならびにカキの育種における DlSx-AF4S を用いたマーカー選抜の可能性が示された．