The CaCAD1-CaPOA1 module positively regulates pepper resistance to cold stress by increasing lignin accumulation

Low-temperature stress is a major environmental constraint, limiting the growth, development, and yield of peppers. Cinnamyl alcohol dehydrogenase (CAD) and peroxidase (POA) are two key enzymes in lignin synthesis, participating in monolignol biosynthesis and monolignol polymerization, respectively. Although CAD and POA are known to play central roles in lignin biosynthesis and plant responses to abiotic stress, their functions in peppers remain poorly understood. In this study, we demonstrated the interaction between CaCAD1 and CaPOA1, which collectively positively regulated lignin biosynthesis in peppers. Additionally, CaCAD1 and CaPOA1 expression was induced by low temperatures, with expression levels gradually increasing with prolonged cold treatment. Silencing of CaCAD1 or CaPOA1 increased the sensitivity of pepper plants to low temperatures. On the other hand, overexpression of CaCAD1 and CaPOA1 in Arabidopsis enhanced its reactive oxygen species scavenging ability and improved plant tolerance to freezing conditions. In summary, the CaCAD1-CaPOA1 module was shown to play a crucial role in pepper cold tolerance, providing valuable insights and targets for future molecular breeding efforts aimed at enhancing pepper cold tolerance.