Ryutaro Tao, Luca Comai and colleagues report the discovery of a small RNA–mediated sex determination pathway in the persimmon, Diospyros lotus (Science 346, 646–650, 2014). The authors sequenced the genomes of 32 female and 25 male plants and identified approximately 800 male-specific contigs, from which they inferred the male-specific Y chromosome region (MSY). Combining their map with RNA sequencing of developing male and female buds, they identified seven male-specific transcripts that mapped to the MSY. One candidate, a predicted homeodomain transcription factor they named OGI, meaning 'male tree' in Japanese, encoded a 21-bp small RNA and showed similarity to an autosome-derived female-specific transcript, which the authors named MeGI ('female tree'). Both genes are orthologs of the barley Vrs1 gene, which is involved in flower development. Analysis of transgenic tobacco and Arabidopsis thaliana plants expressing MeGI and OGI suggested that OGI targets and inhibits expression of MeGI, thereby suppressing feminization. The results also indicated that MeGI might act to sterilize androecia in a dose-dependent manner.