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.

Auxin is throughout the entire life process of plants and is involved in the crosstalk with other hormones, yet its role in apple disease resistance remains unclear. In this study, we investigated the function of auxin/indole-3-acetic acid (IAA) gene MdIAA24 overexpression in enhancing apple resistance to Glomerella leaf spot (GLS) caused by Colletotrichum fructicola (Cf). Analysis revealed that, upon Cf infection, 35S::MdIAA24 plants exhibited enhanced superoxide dismutase (SOD) and peroxidase (POD) activity, as well as a greater amount of glutathione (reduced form) and ascorbic acid accumulation, resulting in less H₂O₂ and superoxide anion (O₂^.−) in apple leaves. Furthermore, 35S::MdIAA24 plants produced more protocatechuic acid, proanthocyanidins B1, proanthocyanidins B2 and chlorogenic acid when infected with Cf. Following Cf infection, 35S::MdIAA24 plants presented lower levels of IAA and jasmonic acid (JA), but higher levels of salicylic acid (SA), along with the expression of related genes. The overexpression of MdIAA24 was observed to enhance the activity of chitinase and β-1,3-glucanase in Cf-infected leaves. The results indicated the ability of MdIAA24 to regulate the crosstalk between IAA, JA and SA, and to improve reactive oxygen species (ROS) scavenging and defense-related enzymes activity. This jointly contributed to GLS resistance in apple.