Structural Characterization and Expression Profiling of Ethylene Biosynthetic Genes During AgNO3-Induced Sex Reversal in Bitter Gourd

Ethylene biosynthetic enzymes, 1-aminocyclopropane-1-carboxylate (ACC) synthase (ACS) and ACC oxidase (ACO), participate in the floral sex differentiation of bitter gourd (Momordica charantia). However, the relationship between their structural features and developmental expression patterns remains to be further clarified. In this study, eight McACS and five McACO genes were identified using the Dali-11 reference genome. AlphaFold 3-based modeling showed structural differences between the two families, particularly regarding the diverse C-terminal flexibilities of McACS proteins. Targeted qRT-PCR profiling during the critical 1.0–3.0 mm early floral bud stage revealed that McACS7, a structurally stable Type III member, along with McACS1, McACS12, and McACO2, were significantly upregulated during natural female flower development. Furthermore, treatment with silver nitrate (AgNO3), an ethylene perception inhibitor, suppressed the transcription of these synthesis genes to basal levels and induced hermaphroditic flower formation. Instead of fully elucidating the downstream molecular mechanisms, these findings provide robust candidate-gene evidence and transcriptional profiling that link the ethylene biosynthetic machinery to the chemically induced sex reversal process, thereby laying a solid foundation for future functional characterization.