Monoecy in an XY yam reveals labile sex expression and hormonal reprogramming in Dioscorea alata.

Dioscorea alata has long been considered strictly dioecious, with male and female flowers borne on separate individuals. Here, we report the first documented case of monoecy and labile sex expression in D. alata, identified in the hybrid CIRAD187. Although previously classified as male, this accession now produces both male and female flowers on the same inflorescence, and a few intermediate flower types, including abortive female flowers. Controlled crosses confirmed the fertility of both flower types. Genotyping with a sex-linked KASP marker revealed that CIRAD187 carries an XY genotype, demonstrating that the Y chromosome alone does not strictly determine male phenotype. Transcriptome profiling across male, female, and intermediate flowers revealed extensive divergence, with up to 8750 differentially expressed genes (DEG) between male and female flowers. Distinct identity modules were detected, with female flowers enriched in proteolysis and MAPK/defense-related pathways, male flowers in transcriptional regulation and secondary metabolism, and intermediate flowers in endomembrane organization and endoplasmic reticulum protein processing. A core set of 481 DEGs was shared across comparisons, and 79 DEGs were located within the sex-determining region, indicating transcriptional plasticity of sex-linked loci. Hormone-related pathways were prominently represented, with 340 jasmonic acid (JA)-associated genes detected across the DEG landscape. JA quantification revealed a consistent gradient (male > intermediate > female), supported by coordinated modulation of biosynthesis and signaling components. These findings uncover unexpected reproductive flexibility in D. alata and provide a molecular framework for understanding and potentially exploiting sex plasticity in greater yam breeding.