Identification of MRS2 Gene Family and Expression Analysis in Response to Magnesium Treatment in Malus domestica

The CorA/MRS2-type transporters represent a crucial family of magnesium ion transporters widely distributed in plants. Through comprehensive screening and alignment using the Phytozome database, we identified seven magnesium-related <i>MdMRS2</i> Confirm the deletion of the "Chinese Province" column in the address. genes in apple (<i>MdMRS2-1</i> to <i>MdMRS2-7</i>), which were distributed across seven distinct chromosomes. Phylogenetic analysis classified these genes into five distinct clades. Tissue-specific expression profiles revealed the differential expression patterns of <i>MdMRS2</i> members in different tissues such as the apple roots, stems, leaves, seedlings, seeds, flowers, and fruits. Among them, the expression level of <i>MdMRS2-5</i> was the highest in fruits, while that of <i>MdMRS2-6</i> was the lowest in seeds. Analysis of <i>cis</i>-regulatory elements in <i>MdMRS2</i> promoter regions identified numerous light-responsive elements, MYB binding sites, and hormone-responsive elements, suggesting their transcriptional regulation may be influenced by related metabolic pathways or signaling molecules. qRT-PCR results showed that the relative expression levels of all genes were significantly upregulated compared with CK under M3 treatment, while there were no significant differences in other treatments. Among them, the upregulation of <i>MdMRS2-7</i> was the most significant, increasing by 142% compared with CK. Notably, all <i>MdMRS2</i> genes were significantly upregulated under 4 mmol·L^-1 MgSO₄ treatment. Subcellular localization experiments conducted in tobacco leaves confirmed the membrane and cytoplasmic distribution of these transporters, consistent with bioinformatic predictions. These genes may become candidate genes for subsequent functional studies. This work will provide a basis for future research on the response mechanism and function of the MRS2 gene family in response to magnesium stress.