Actinidia arguta AaMYB4 Confers Cold and Drought Tolerance Through Up-Regulating Antioxidant Capacity Associated with the ROS Scavenging

Actinidia arguta possesses great commercial value as an economically important fruit crop, which accumulates abundant nutrients and bioactive components with medicinal potential. However, adverse abiotic environments, especially cold and drought stress, severely restrict its vegetative growth, reproductive development and fruit yield. Numerous studies have established MYB transcription factors as core regulators of plant abiotic stress adaptation. Here, we cloned AaMYB4 from A. arguta ‘Fenglü’ and systematically characterized its function in cold and drought tolerance. AaMYB4 encodes a 241-amino-acid R2R3-MYB protein localized to the nucleus, with highest expression in stems and young leaves. Its transcription is markedly induced by cold, drought and abscisic acid (ABA) within 24 h with a single peak expression pattern. Heterologous overexpression of AaMYB4 in Arabidopsis alleviated cold-induced oxidative damage, accompanied by reduced malondialdehyde (MDA) and reactive oxygen species (ROS) accumulation as well as increased proline contents and enhanced superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) activities. Virus-induced gene silencing (VIGS)-mediated silencing of AaMYB4 impaired cold tolerance in Actinidia arguta seedlings, while stable AaMYB4 overexpression significantly improved plant survival and physiological performance under cold and drought conditions, concurrent with attenuated ROS accumulation. At the transcriptional level, AaMYB4 overexpression is positively associated with elevated transcript levels of stress marker genes in the ABA signaling and ICE1-CBF-COR pathways. This study lays a theoretical foundation for exploring abiotic stress tolerance mechanisms and conducting stress-resistant molecular breeding in A. arguta.