Abstract: 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.

Key words: chlorophyll degradation, CsERF113L, cucumber, ethylene synthesis, saline–alkali stress