Phylogenetic and expression analysis of the magnesium transporter family in pear, and functional verification of <i>PbrMGT7</i> in pear pollen

The magnesium ion (Mg²⁺) is the most abundant divalent cation in living cells, and it plays essential roles in various cellular functions. Mg²⁺ homeostasis in plant cells is crucial for plant growth. The <i>MRS2</i>/<i>MGT</i> family of proteins localise to various membranes, and they function during Mg²⁺ transport in plants, but their functions are largely unknown in fruit trees. In this study, we performed a genome-wide analysis to identify the <i>MGT</i> gene family members in the pear <i>Pyrus bretschneideri</i>. Sixteen <i>MGT</i> genes were identified. Analysis of the activity of pear pollen showed that a low-concentration magnesium ion treatment was beneficial for pollen germination and pollen tube growth. None of the 16 <i>MGT</i> genes were expressed in any unique tissue, including pollen, and their expression in magnesium-treated pollen varied greatly, where <i>PbrMGT7</i> was the most sensitive and it was tested as a representative. <i>PbrMGT7</i> could functionally complement a bacterial strain deficient in Mg²⁺, thereby indicating a role in magnesium transport. A co-localisation experiment confirmed that <i>PbrMGT7</i> was localised in the mitochondria, which suggests that <i>PbrMGT7</i> could mediate Mg-trafficking between the mitochondria and cytosol. Overall, these results suggest that <i>PbrMGT7</i> is related to Mg²⁺ homeostasis during pear pollen tube growth.​​