Ogi, a Y-Encoded Small-RNA, Acts for Sex Determination in Diospyros Plant Species

In plants, multiple lineages have evolved sex chromosomes independently, providing rich material for comparison. Yet, so far, no specific determinant controlling sexuality has been identified. We investigated sex-determinants in Caucasian persimmon, Diospyros lotus, a dioecious species with heterogametic males (XY). Here we show that, even in the absence of any prior genomic information from this species, cataloging and assembling male-specific short nucleotide genomic sequences defined a male determining region on the Y chromosome. On this region, candidate genes expressed in flower primordia were defined by comparison to assembled transcriptomes. Next, evolutionary approaches exploiting historical recombination between the X and Y chromosomes and genetic drift in a wide variety of Diospyros species were applied. Together, these approaches led to the identification of one Y-specific sex-determinant candidate, OGI, displaying completely male-specific conservation among Diospyros species. OGI encodes an inverted repeats producing a small RNA that in turn triggers transitive RNAi on the autosomal MeGI gene. Both OGI and MeGI sequences are homologous to homeodomain transcription factors, and their divergence is expected to predate the origin of Diospyros genus. Transgenic experiments in A. thaliana and N. tabacum confirm a feminizing role for MeGI. Furthermore, we found that MeGI promoter methylation is tightly associated with flower sexuality in monoecious individuals of hexaploid D. kaki (oriental persimmon), providing an attractive model for flexible sex determination by epigenetic regulations in a polyploidy system.