Cadmium (Cd) stress is a serious threat to apple growth and development. Ethylene response factors (ERFs) are a major family of transcription factors (TFs) that play a key role in the resistance to Cd stress. In this study, we found that the ERF TF MdERF114 was induced in response to Cd stress. The overexpression of MdERF114 in apple (Malus domestica) roots reduced the accumulation of Cd in the plants and enhanced their tolerance to Cd stress. Yeast one-hybrid (Y1H) assays, dual-luciferase assays, and electrophoretic mobility shift assays indicated that MdERF114 directly binds to the promoter of MdATG16 and activates its expression to increase autophagic activity, which leads to higher resistance to Cd stress. In addition, MdMYB306 interacts with MdERF114 and enhances the resistance to Cd stress by promoting the binding of MdERF114 to the promoter of MdATG16. Our findings reveal an important mechanism by which MdMYB306-MdERF114-MdATG16 influences the resistance of apple to Cd stress.

The pivotal role of N⁶-methyladenosine (m⁶A) demethylases in regulating plant stress responses has been widely explored; however, the function of apple m⁶A demethylases under heat stress and fixed-carbon starvation is unclear. In this study, the apple RNA demethylase gene family was identified, and the demethylase gene MdALKBH1A was selected for further analysis. Using liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis, we demonstrated that MdALKBH1A is the m⁶A demethylase of apple. Moreover, transgenic ‘Micro Tom’ tomato plants overexpressing MdALKBH1A were more sensitive to high temperature, probably due to the decreased antioxidant ability, increased membrane lipid peroxidation and reduced plasma membrane stability. However, these tomato plants overexpressing MdALKBH1A were more resistant to fixed-carbon starvation, as evidenced by the improved plasma membrane stability, enhanced photosynthetic rates and elevated autophagic activity. In summary, our results highlight the crucial role played by MdALKBH1A in the response of apple plants to high-temperature stress and fixed-carbon starvation.

Abiotic stress reduces plant yield and quality. WRKY transcription factors play key roles in abiotic stress responses in plants, but the molecular mechanisms by which WRKY transcription factors mediate responses to drought and osmotic stresses in apple (Malus × domestica Borkh.) remain unclear. Here, we functionally characterized the apple Group Ⅲ WRKY gene MdWRKY115. qRT-PCR analysis showed that MdWRKY115 expression was up-regulated by drought and osmotic stresses. GUS activity analysis revealed that the promoter activity of MdWRKY115 was enhanced under osmotic stress. Subcellular localization and transactivation assays indicated that MdWRKY115 was localized to the nucleus and had a transcriptional activity domain at the N-terminal region. Transgenic analysis revealed that the overexpression of MdWRKY115 in Arabidopsis plants and in apple callus markedly enhanced their tolerance to drought and osmotic stresses. DNA affinity purification sequencing showed that MdWRKY115 binds to the promoter of the stress-related gene MdRD22. This binding was further verified by an electrophoretic mobility shift assay. Collectively, these findings suggest that MdWRKY115 is an important regulator of osmotic and drought stress tolerance in apple.