Identification and Expression of the CorA/MRS2/ALR Type Magnesium Transporters in Tomato

Magnesium (Mg(2+)) is the most abundant divalent ion in plants, participating in numerous metabolic processes in growth and development. CorA/MRS2/ALR type Mg(2+) transporters are essential for maintaining Mg(2+) homeostasis in plants. However, the candidate protein and its potential functions in the tomato plant have not been fully understood. In this study, we identified seven MGT genes (SlMRS2) in tomato based on sequence similarity, domain analysis, conserved motif identification, and structure prediction. Two SlMRS2 genes were analyzed in the bacterial strain MM281, and a functional complementary assay demonstrated their high-affinity transport of Mg(2+). Quantitative real-time PCR analysis revealed that the expressions of these Mg(2+) transporters were down-regulated in leaves under Mg(2+) limitation, with a greater impact on lower and middle leaves compared to young leaves. Conversely, under Mg(2+) toxicity, several genes were up-regulated in leaves with a circadian rhythm. Our findings indicate that members of the SlMRS2 family function as Mg(2+) transporters and lay the groundwork for further analysis of their distinct functions in tomato.