Sex differentiation is fundamental for the reproduction and genetic diversity of most eukaryotes, including land plants. In the liverwort Marchantia polymorpha, sex differentiation is controlled by a single autosomal locus consisting of a female-promoting transcription factor gene, FGMYB, and the SUF antisense long-non-coding RNA (lncRNA). While SUF is known to suppress FGMYB transcription to promote male differentiation, the underlying mechanism has remained unknown. In this issue, Kajiwara et al. have elucidated the molecular basis of FGMYB suppression by SUF. By using CRISPR/Cas9-mediated large-deletion mutants lacking the entire FGMYB-SUF locus sequence in various transgene complementation tests, the authors found that SUF transcription, rather than its transcripts, is required for FGMYB suppression. This finding provides insight into the mechanisms by which lncRNAs regulate sexual reproduction in land plants. See also Commentary by Hisanaga, in this issue.