ABA enhances drought tolerance in tomato seedlings and is partially dependent on SlDML2-directed DNA demethylation

Abscisic acid (ABA) is a phytohormone that alleviates drought stress in many plant species. DNA methylation also plays an important role in plant drought stress tolerance. However, the relationship between ABA and DNA demethylase is unclear. Here, the action mechanism of tomato DEMETER-LIKE protein 2 (DML2) in ABA-mediated drought stress resistance was studied by mutating SlDML2. We found that the mutation of SlDML2 weakened plant growth under drought stress. Additionally, the content of chlorophylls, osmoregulatory substances (proline, soluble sugar, and soluble protein), and flavonoids were lower in sldml2-1 mutants under drought circumstances when compared with wild-type (WT) plants. However, these effects of the mutated SlDML2 could not be reversed by the application of ABA. Furthermore, the expression levels of SlPYL1 and SlSnRK2.4 in the ABA signaling pathway were downregulated in sldml2-1 mutants under drought stress compared with WT plants. Moreover, exogenous ABA reduced the DNA methylation level and the transcriptional abundance of its regulated genes by altering SlDML2-driven DNA demethylation under drought stress. This study here demonstrates the important role of SlDML2 in ABA-improved plant drought tolerance, which may facilitate studies concerning ABA and DNA demethylation in the future.