The CsRAP2.12–CsERF113L/CsRAP2.7 module positively regulates chlorophyll degradation to impair saline–alkali tolerance in cucumber

Soil salinization poses a global threat to agricultural productivity by degrading arable land. Preventing the rapid degradation of chlorophyll caused by saline-alkali stress is a crucial means to improve plant resistance and productivity. In this study, RNA sequencing identified CsPPH, a pheophytinase-encoding gene that functions as a negative regulator of both photosynthesis and saline-alkali tolerance in cucumber (Cucumis sativus L.). Saline-alkali stress rapidly induces the expression of related to APETALA2 2.12 (CsRAP2.12). Subsequently, CsRAP2.12 activates the transcription of both ethylene response factor 113-like (CsERF113L) and CsRAP2.7, while CsERF113L further transcriptionally regulates CsRAP2.7. CsERF113L promotes chlorophyll degradation and reactive oxygen species (ROS) accumulation both through direct transcriptional upregulation of CsPPH, chlorophyll b reductase (CsNYC1), and chlorophyllase 2 (CsCLH2) and by indirectly stimulating ethylene synthesis via upregulation of 1-aminocyclopropane-1-carboxylic acid synthase 6/9/10 (CsACS6/9/10), thereby impairing photosynthesis and accelerating senescence. CsRAP2.7 indirectly promotes saline-alkali stress-induced chlorophyll degradation and photosynthetic inhibition by facilitating CsERF113L-mediated transcriptional activation of CsPPH, CsCLH2, and CsACS6/9/10. Therefore, knockout of either CsRAP2.12, CsERF113L, or CsRAP2.7 significantly alleviated chlorophyll degradation and enhanced photosynthetic performance under saline-alkali stress, ultimately improving antioxidant capacity and stress tolerance. These findings reveal that the CsRAP2.12-CsERF113L/CsRAP2.7 module promotes saline-alkali stress-induced chlorophyll degradation and photosynthetic inhibition via a dual regulatory mechanism. Genetic disruption of this module significantly improves cucumber tolerance to saline-alkali stress.