Sex-specific ethylene responses drive floral sexual plasticity in Cannabis sativa

Cannabis sativa L. exhibits pronounced sexual plasticity in which both XX and XY plants can undergo floral phenotypic sex reversal in response to ethylene modulation, yet the underlying molecular mechanisms remain poorly defined. Here, we present the most extensive multi-omic analysis of ethylene-induced sex change in C. sativa to date, integrating over 130 RNA-seq libraries, ethylene pathway metabolite quantification, and whole-genome sequencing across three XX and XY genotypes. Treatments with silver thiosulfate and ethephon induced more than 80% phenotypic conversion, but transcriptomic responses diverged sharply between XX and XY plants. Profiling 47 ERGs revealed 14 high-confidence candidates, including CsACS1, CsACO5, CsERF1, and CsMTN, with sex-specific and temporal expression patterns that show dynamic ethylene mediation of plasticity. Early transcriptional activation occurred prior to the emergence of flowers, within 18 h of sex-change treatments and the photoperiod-induced transition to flowering. As opposite-sex floral tissues emerged, ethylene-related gene expression shifted accordingly within developing floral organs, with distinct sets of genes stabilizing the opposite-sex phenotype in XX and XY plants. Several candidates were located in non-recombining regions of the X chromosome or were absent from the Y chromosome, and most exhibited low nucleotide diversity, consistent with functional constraint. These results provide a high-resolution view of ethylene-responsive sexual plasticity in cannabis and show that the shared capacity for sex reversal in XX and XY plants is implemented through distinct regulatory trajectories that produce opposite-sex floral phenotypes. This work expands the mechanistic understanding of sex expression in dioecious species and identifies candidate genes relevant to the development of sex-stable cultivars.