The calcium-dependent protein kinase CmaCPK4 regulates sex determination in pumpkin (Cucurbita maxima D.).

This article focuses on the identification and functional characterization of the calcium-dependent protein kinase gene CmaCPK4 as a regulator of sex determination in pumpkin (Cucurbita maxima). The study mapped a recessive locus, sg1, controlling the subgynoecious trait—characterized by a high ratio of female to male flowers—to chromosome 2, where a retrotransposon insertion in the CmaCPK4 promoter was found to elevate its expression. CmaCPK4 interacts with and phosphorylates ethylene biosynthesis enzymes CmaACS5 and CmaACS7, increasing ethylene production, which promotes female flower development and the subgynoecious phenotype. Overexpression of CmaCPK4 in cucumber similarly increased female flower ratio, supporting its role in ethylene-mediated sex determination. These findings elucidate a molecular mechanism involving the CmaCPK4–CmaACS5/7 module that modulates ethylene-induced sex expression in pumpkin.