Silencing of CsDMC1 Suppresses Meiotic Recombination and Reduces Pollen Viability in Cucumber (Cucumis sativus L.)

Cucumber ( Cucumis sativus L.) is a globally significant vegetable crop, and targeted manipulation of its recombination frequency offers opportunities to broaden genetic diversity and enable novel breeding applications. In the first stage of this study, we characterized the spatial activity of the cucumber DMC1 ( CsDMC1 ) promoter in cucumber. Subsequently, we investigated the effects of CsDMC1 silencing on meiotic recombination and pollen viability of cucumber. Transgenic plants expressing the GUS reporter gene under the control of the CsDMC1 promoter exhibited strong GUS activity in the microspores, but no detectable expression in vegetative tissues or seeds, confirming the meiosis-specific activity. RNAi-mediated silencing of CsDMC1 in cucumber resulted in variable downregulation (67–94%) across transgenic lines, correlating strongly with pollen abortion rates (16–90%, r = 0.87). Meiotic crossover frequency was evaluated using two polymorphic SSR markers in a non-transgenic cucumber plant and a transgenic line exhibiting approximately 80% reduction in CsDMC1 expression and 55% pollen abortion, revealing a 46% decrease in crossover frequency in the transgenic line compared with the control. Importantly, the results indicate that although CsDMC1 silencing effectively suppresses recombination, the cellular abundance of CsDMC1 likely exceeds the minimum requirement for normal crossover formation, and its overexpression alone may not increase crossover frequency beyond a natural threshold. Our findings highlight CsDMC1 silencing as a practical tool for reverse breeding in cucumber and underscore the utility of the CsDMC1 promoter as a meiosis-specific driver for future studies.