Unlocking the role of ClDYAD in initiating meiosis: A functional analysis in watermelon

Watermelon (Citrullus lanatus), one of the top five fruit crops based on the gross tonnage and cultivated area globally, holds major economic importance in agriculture and contributes substantially to farmers’ incomes. Watermelon cultivation relies on sexual reproduction, with meiosis playing a pivotal role in this process. However, our understanding of the meiotic mechanism in watermelon remains limited. In this study, we utilized CRISPR/Cas9 technology to target ClDYAD, a homolog of the meiosis-related genes AtDYAD and OsAM1, and conducted functional analysis to explore the initiation of meiosis in watermelon. ClDYAD was highly expressed in tender male flowers both before and during the early stages of meiosis. Mutations in ClDYAD led to meiotic arrest at the leptotene stage, impeding the normal enlargement of microspore mother cells and megasporocytes. This resulted in the absence of pollen in anthers and seed abortion. ClDYAD physically interacts with the protein encoded by Cla97C07G137480, which was identified as a switch-associated protein 70-like protein (ClSWAP-70). The expression pattern of ClSWAP-70 in tender male flowers of various sizes matched with the changes in ClDYAD mRNA levels. These findings shed light on the molecular mechanisms governing the initiation of meiosis in watermelon, offering valuable insights into male and female sterility in Cucurbitaceae plants and guiding future research.