CabZIP42 mediates ALA-regulated saline-alkali tolerance by enhancing the expression level of CaSOS1 and CaPOX2 in pepper seedlings

Saline-alkali stress is a major environmental challenge affecting agricultural production worldwide. Our previous study demonstrated that 5-aminolevulinic acid (ALA), an exogenous plant growth regulator, enhances saline-alkali tolerance in pepper plants. However, the underlying regulatory mechanism remains unclear. In this study, we identified a transcription factor, CabZIP42 , which was significantly up-regulated in pepper plants treated with ALA under saline-alkali stress, suggesting its potential involvement in ALA-mediated saline-alkali tolerance. Silencing of CabZIP42 compromised saline-alkali tolerance, as evidenced by increased accumulation of reactive oxygen species (ROS) and malondialdehyde (MDA), elevated Na⁺/K⁺ ratio, and reduced activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT). Conversely, over-expression of CabZIP42 in pepper and Arabidopsis thaliana enhanced the activities of SOD, POD, and CAT, up-regulated the expression of saline-alkali stress-related genes ( CaNHX1 , CaPOD , CaSOS1 , CaCAT , CaPOX2 ), and decreased ROS accumulation and Na⁺/K⁺ ratio. Furthermore, CabZIP42 might bind to the promoters of CaSOS1 (a Na⁺ transport gene) and CaPOX2 (a POD-related gene) and activate their expression. Our findings indicate that ALA enhances saline-alkali tolerance by inducing CabZIP42 expression, which might in turn transcriptionally activate downstream genes involved in ion homeostasis and ROS scavenging. These results provide new insights for molecular breeding of saline-alkali tolerant pepper varieties.