Transcription factor ClTCP4 maintains watermelon resilience to drought by stabilizing antioxidant and photosynthetic systems.

Key message: ClTCP4 mitigates the damage of the cellular membrane and photosystem impairment from reactive oxygen species (ROS) under drought conditions by maintaining the generation of antioxidant enzymes and osmotic regulatory substances. The increasing occurrence of extreme weather events in recent years has intensified water scarcity in watermelon cultivation, significantly reducing both yield and quality. At present, the exploration of watermelon drought resistance genes is limited, which limits the use of molecular breeding for drought resistance. In current study, we identified CINCINNATA (CIN) subclass members of the TEOSINTE BRANCHED 1/CYCLOIDEA/PCF (TCP) family in watermelon through sequence alignment and homologous clustering analysis. Analysis of the gene expression characteristics showed that CIN-TCP members are induced by exogenous hormones and abiotic stresses. Specifically, the ClTCP4 is significantly induced by dehydration stress and abscisic acid (ABA). The gene-edited lines (CR lines) of ClTCP4 were constructed and were used to confirm its role in regulating the drought tolerance. Under drought stress, CR lines showed earlier leaf wilting, smaller stomatal opening, lower leaf water holding capacity and photosynthetic efficiency compared with YL plants. By combining phenotypic observation, physiologic, biochemical, and molecular experiments, our study reveals that ClTCP4 regulates the photosynthesis-related processes under drought stress through stomatal conductance pathway, mitigates the damage of the cellular membrane and possible photosystem impairment from reactive oxygen species (ROS) under drought conditions by maintaining the generation of antioxidant enzymes and osmotic regulatory substances. This study elucidates the role of ClTCP4, a member of CIN-TCP in drought stress, and could provide a theoretical foundation and gene resource for watermelon drought resistance breeding.