An introduction to the Mg2+ transporters in plants

Magnesium (Mg) is one of the essential macroelements for all living cells, and the Mg2+ concentration in each organelle is maintained appropriately. Over the past two decades, knowledge on Mg2+ transporters has been accumulating. The major Mg2+ transporters in plant are Mrs2/MGT family CorA-Mrs2-ALR-type transporters. They were firstly identified in Arabidopsis and then in rice, and now the analysis is rapidly proceeding in a variety of crops. Mrs2/MGT proteins are localized in the vacuolar membrane, mitochondrial membrane, chloroplast, endoplasmic reticulum, and plasma membrane, respectively, and defects in some of them have been shown to be critical enough to interfere with plant development, especially under fluctuating Mg environment. MHX type vacuolar transporters, and some proteins of plasma membrane-localized cyclic nucleotide-gated channels and HKT type transporters can also participate in Mg2+ transport. NIPA family proteins are also potential Mg2+ transporters, yet to be functionally characterized. This chapter describes what we know so far about tissue distribution, subcellular localization, ion transport activity, and mutant phenotypes for each transporter.