Although hundreds of plant lineages have independently evolved dioecy (that is, separation of the sexes), the underlying genetic basis remains largely elusive¹. Here we show that diverse poplar species carry partial duplicates of the ARABIDOPSIS RESPONSE REGULATOR 17 (ARR17) orthologue in the male-specific region of the Y chromosome. These duplicates give rise to small RNAs apparently causing male-specific DNA methylation and silencing of the ARR17 gene. CRISPR–Cas9-induced mutations demonstrate that ARR17 functions as a sex switch, triggering female development when on and male development when off. Despite repeated turnover events, including a transition from the XY system to a ZW system, the sex-specific regulation of ARR17 is conserved across the poplar genus and probably beyond. Our data reveal how a single-gene-based mechanism of dioecy can enable highly dynamic sex-linked regions and contribute to maintaining recombination and integrity of sex chromosomes.

尽管数百种植物谱系已经独立进化出雌雄异体（即两性分离），但其潜在的遗传基础仍然很难捉摸¹。在这里，我们显示了不同的杨树物种在Y染色体的雄性特异性区域中携带着阿拉伯拟南芥响应调节剂17（ARR17）直向同源物的部分重复。这些重复产生明显引起男性特异性DNA甲基化和ARR17基因沉默的小RNA 。CRISPR–Cas9诱导的突变表明ARR17用作性开关，开启时触发女性发育，关闭时触发男性发育。尽管发生了反复的周转事件，包括从XY系统过渡到ZW系统，但ARR17的性别特异性调节在整个杨树属中都可能得到保护，甚至可能更远。我们的数据揭示了基于单基因的雌雄异体机制如何能够实现高度动态的性链接区域，并有助于维持性染色体的重组和完整性。