The transcription factor MhZAT10 enhances antioxidant capacity by directly activating the antioxidant genes MhMSD1, MhAPX3a, and MhCAT1 in apple rootstock SH6 (Malus honanensis × M. domestica)

Stress tolerance in apple (Malus domestica) can be improved by grafting to a stress-tolerant rootstock, such as 'SH6' (Malus honanensis × M. domestica 'Ralls Genet'). However, the mechanisms of stress tolerance in this rootstock are unclear. In Arabidopsis (Arabidopsis thaliana), the transcription factor ZINC FINGER OF ARABIDOPSIS THALIANA 10 (ZAT10) is a key component of plant tolerance to multiple abiotic stresses and positively regulates antioxidant enzymes. However, how reactive oxygen species (ROS) are eliminated upon activation of ZAT10 in response to abiotic stress remains elusive. Here, we report that MhZAT10 in the rootstock SH6 directly activates the transcription of three genes encoding the antioxidant enzymes MANGANESE SUPEROXIDE DISMUTASE 1 (MhMSD1), ASCORBATE PEROXIDASE 3A (MhAPX3a), and CATALASE 1 (MhCAT1) by binding to their promoters. Heterologous expression in Arabidopsis protoplasts showed that MhMSD1, MhAPX3a, and MhCAT1 localize in multiple subcellular compartments. Overexpressing MhMSD1, MhAPX3a, or MhCAT1 in SH6 fruit calli resulted in higher superoxide dismutase, ascorbate peroxidase, and catalase enzyme activities in their respective overexpressing calli than in those overexpressing MhZAT10. Notably, the calli overexpressing MhZAT10 exhibited better growth and lower ROS levels under simulated osmotic stress. Apple SH6 plants overexpressing MhZAT10 in their roots via Agrobacterium rhizogenes-mediated transformation also showed enhanced tolerance to osmotic stress, with higher leaf photosynthetic capacity, relative water content in roots, and antioxidant enzyme activity, as well as less ROS accumulation. Overall, our study demonstrates that the transcription factor MhZAT10 synergistically regulates the transcription of multiple antioxidant-related genes and elevates ROS detoxification.