Discovery and characterization of magnesium transporter (MGT) gene family in Citrus sinensis and their role in magnesium deficiency stress

The divalent cation Magnesium (Mg2+) is necessary for healthy plant development, growth, and defense. Plants acquire Mg2+ from the soil and transport it throughout their body tissues with Mg2+ transporter (MGT) proteins. Although several MGT genes have been discovered and described in rice, maize, and Arabidopsis, far less information is available regarding their diversity and function in other plant species. To address this knowledge gap, here we identified seven putative MGT genes (CsMGT1-CsMGT7) in Citrus sinensis, which were classified into four distinct clades through phylogenetic analysis. Gene structures, cis-acting regulatory elements, and conserved motifs were also analyzed. Quantitative real-time PCR (qRT-PCR) indicated that the seven CsMGT genes were constitutively expressed across a variety of plant tissues, with the exception of CsMGT5, which lacked detectable expression in fruit peels and pulp. Furthermore, qRT-PCR indicated that the seven CsMGT genes responded differently to Mg2+ deprivation in leaves and roots. Complementation assays using Salmonella typhimurium MM281 and yeast CM66 demonstrated that CsMGT7 possessed the strongest Mg2+ transport capacity. We propose that CsMGT7 might serve as an Mg2+ transporter and play a crucial role in Mg2+ deficiency response. Our results will aid future research on the biological roles of MGTs in plants, which is beneficial for combining theoretical and application-based research in fruit plants.