VvATG6 contributes to copper stress tolerance by enhancing the antioxidant ability in transgenic grape calli

Autophagy, a conserved degradation and reuse process, plays a crucial role in plant cellular homeostasis during abiotic stress. Although numerous autophagy-related genes (ATGs) that regulate abiotic stress have been identified, few functional studies have shown how they confer tolerance to copper (Cu) stress. Here, we cloned a novel Vitis vinifera ATG6 gene (VvATG6) which was induced by 0.5 and 10 mM Cu stress based on transcriptomic data, and transgenic Arabidopsis thaliana, tobacco (Nicotiana tabacum), and grape calli were successfully obtained through Agrobacterium-mediated genetic transformation. The overexpression of VvATG6 enhanced the tolerance of transgenic lines to Cu. After Cu treatment, the lines that overexpressed VvATG6 grew better and increased their production of biomass compared with the wild-type. These changes were accompanied by higher activities of antioxidant enzymes and a lower accumulation of deleterious malondialdehyde and hydrogen peroxide in the transgenic plants. The activities of superoxide dismutase, peroxidase, and catalase were enhanced owing to the elevation of corresponding antioxidant gene expression in the VvATG6 overexpression plants under Cu stress, thereby promoting the clearance of reactive oxygen species (ROS). Simultaneously, there was a decrease in the levels of expression of RbohB and RbohC that are involved in ROS synthesis in transgenic plants under Cu stress. Thus, the accelerated removal of ROS and the inhibition of its synthesis led to a balanced ROS homeostasis environment, which alleviated the damage from Cu. This could benefit from the upregulation of other ATGs that are necessary for the production of autophagosomes under Cu stress. To our knowledge, this study is the first to demonstrate the protective role of VvATG6 in the Cu tolerance of plants.