Genome-wide analysis of MdABF Subfamily and functional identification of MdABF1 in drought tolerance in apple

Abscisic acid (ABA) is an important hormone involved in plant growth and adaptation to environmental stress. Abscisic acid-responsive elements (ABRE)-binding transcription factors (ABFs) are important transcription factors involved in the ABA signaling pathway that participate in various biological processes in plants. The functions of ABF members are largely unknown in Malus domestica. In this study, sixteen Malus domestica ABF (MdABF) family members were identified in the apple (Malus x domestica) genome. The phylogenetic tree, chromosomal locations, promoter region cis-acting elements, gene structures, and conserved motifs of these MdABF members were analyzed. Subsequently, gene expression level analysis revealed that MdABFs had differential gene expression patterns in response to multiple abiotic factors, and most MdABF genes were highly expressed in leaves. According to the gene expression pattern analysis, we found that MdABF1 may play an important role in various stress responses. Subsequently, the MdABF1 gene was cloned and transgenic Arabidopsis thaliana material was obtained for further research. Subcellular localization revealed that the transcription factor MdABF1 was localized to the nucleus. Moreover, MdABF1-overexpression in Arabidopsis reduced its resistance to drought, however, there was no observed difference under salt exposure treatment. Meanwhile, expression of MdABF1 promoted early flowering and leaf senescence under drought conditions. These results indicate that MdABF1 may be a pivotal regulator of plant growth under drought conditions. Our findings lay the foundation for further exploration of the functions of MdABF in plant growth and development.