Peanut 9-cis-epoxycarotenoid Dioxygenase Enhances Salt and Drought Stress Tolerance by Regulating ROS Homeostasis

Peanut (<i>Arachis hypogaea</i> L.), a vital oilseed and cash crop, faces yield limitations due to abiotic stresses. The 9-<i>cis</i>-epoxycarotenoid dioxygenase (NCED) enzyme, a key enzyme in abscisic acid (ABA) biosynthesis regulating plant development and stress responses, remains mechanistically uncharacterized in peanut abiotic stress tolerance. In this study, we isolated a novel gene, <i>AhNCED4</i>, from the salt-tolerant mutant M24. The expression of <i>AhNCED4</i> was strongly induced by NaCl, PEG6000, and ABA in peanut huayu20. Overexpression of <i>AhNCED4</i> enhanced salt and drought tolerance in <i>Arabidopsis</i>. Transgenic overexpression of <i>AhNCED4</i> improved salt and stress resistance through upregulated ROS-scavenging genes superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) with elevated enzymatic activities while reducing malondialdehyde (MDA), superoxide anion (O^2-), and hydrogen peroxide (H₂O₂) accumulation compared to wild-type plants. Further research showed that the chlorophyll fluorescence parameters of transgenic lines were significantly increased, while light damage was significantly reduced. These findings establish <i>AhNCED4</i> as a critical regulator of stress adaptation and an excellent candidate gene for resistance breeding in peanut.