CsIPT1b and CsUGT85A2 delay female corolla opening in cucumber by regulating the content of cytokinins

Corolla opening is essential for the propagation of unisexual flowering plants,meanwhile commodity fruits with opening corolla have higher commodity value in cucumber fresh food market.Until now,there is little research on the mechanism of corolla opening in cucumber.In a previous paper,we identified a unique cucumber(Cucumis sativus)line(‘6457’)that possesses super ovaries and shows delayed corolla opening when nutrient supplies are abundant.We also previously showed that the expression of CsIPT1b(isopentenyl transferase)and CsUGT85A2(cytokinin glycosyltransferase)is correlated with the delayed opening of the female corolla.Here,we investigated the mechanism of delayed female corolla opening in cucumber by conducting transgenic experiments,hormone assays,and yeast one-hybrid assays.CsIPT1b and CsUGT85A2 positively and negatively regulated delayed female corolla opening,respectively.In CsIPT1b-overexpressing plants and CsUGT85A2 knockout plants,the content of the trans-zeatin riboside,trans-zeatin,and N6-isopentenyladenosine was increased.Overall,our findings indicate that CsIPT1b and CsUGT85A2 were important regulators of the timing of female corolla opening.These genes could thus be targets to cucumber molecular breeding of fruit with flowers remaining on the tip.