AcMYB176-Regulated AcCHS5 Enhances Salt Tolerance in Areca catechu by Modulating Flavonoid Biosynthesis and Reactive Oxygen Species Scavenging

High-salinity stress induces severe oxidative damage in plants, leading to growth inhibition through cellular redox imbalance. Chalcone synthase (CHS), a pivotal enzyme in the flavonoid biosynthesis pathway, plays critical roles in plant stress adaptation. However, the molecular mechanisms underlying CHS-mediated salt tolerance remain uncharacterized in Areca catechu L., a tropical crop of high economic and ecological significance. Here, we systematically identified the CHS gene family in A. catechu and revealed tissue-specific and salt-stress-responsive expression patterns, with AcCHS5 exhibiting the most pronounced induction under salinity. Transgenic Arabidopsis overexpressing AcCHS5 displayed enhanced salt tolerance compared to wild-type plants, characterized by elevated activities of antioxidant enzymes: superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD), increased flavonoid accumulation, and reduced reactive oxygen species (ROS) accumulation. Furthermore, we identified the transcription factor AcMYB176 as a direct activator of AcCHS5 through binding to its promoter. Our findings demonstrate that the AcMYB176-AcCHS5 regulatory module enhances salt tolerance by orchestrating flavonoid biosynthesis and ROS scavenging. This study provides functional evidence of CHS-mediated salt adaptation in A. catechu and highlights its potential for improving stress resilience in tropical crops.