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 CsRAP2.12, thereby promoting its positive transcriptional regulation of CsERF113L and CsRAP2.7, as well as CsERF113L-mediated positive transcriptional regulation of CsRAP2.7. CsERF113L dually promoted chlorophyll degradation and reactive oxygen species (ROS) accumulation via direct upregulation of CsPPH, CsNYC1, and CsCLH2 transcription, and indirect promotion of ethylene synthesis by upregulating CsACS6/9/10 transcription, ultimately impairing photosynthesis and accelerating plant senescence. CsRAP2.7 indirectly promoted saline-alkali stress-induced chlorophyll degradation and photosynthetic inhibition by facilitating CsERF113L-mediated transcriptional activation of CsPPH 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 CsRAP2.12-CsERF113L/CsRAP2.7 promotes saline-alkali stress-induced chlorophyll degradation and photosynthetic inhibition via a dual regulatory mechanism. Knockout of members in this transcriptional regulatory module significantly enhances the saline-alkali tolerance of plants.