Jasmonate regulates male sterility in cucumber

Male sterility affects various agronomic traits. Although jasmonate (JA) has been shown to influence fertility in several plant species, most research on JA-mediated regulation of fertility has focused on bisexual flowers, leaving the role of this phytohormone in unisexual flowering plants largely unexplored. Cucumber (Cucumis sativus) has unisexual flowers and is an ideal model plant for studying male and female gametophyte development. In this study, we determined that JA regulates male and female flower development as well as male fertility in cucumber. In the JA biosynthesis-deficient mutant Csopr3, both female and male flower petals failed to open properly, anthers showed defective dehiscence, and pollen in male flowers ruptured and was nonviable. MeJA treatment restored normal petal opening and anther dehiscence in Csopr3, and the pollen regained the ability to germinate. Further analysis revealed that CsXTH33, a gene involved in cell-wall structure, negatively regulates stamen fertility in cucumber. Transcriptional regulation assays indicated that CsMYC2 binds to the promoters of CsWRKY45 and CsWRKY57 and activates their expression. In turn, CsWRKY45 and CsWRKY57 bind to the promoter of CsXTH33, inhibiting its expression and promoting normal stamen development. This study thus reveals the role of JA in cucumber unisexual flower development and deepens our understanding of the mechanisms by which JA regulates plant fertility.