Conserved mechanism for vacuolar magnesium sequestration in yeast and plant cells

Magnesium (Mg 2+ ) is an essential nutrient for all life forms. In fungal and plant cells, the majority of Mg 2+ is stored in the vacuole but mechanisms for Mg 2+ transport into the vacuolar store are not fully understood. Here we demonstrate that members of ancient conserved domain proteins (ACDPs) from Saccharomyces cerevisiae and Arabidopsis thaliana function in vacuolar Mg 2+ sequestration that enables plant and yeast cells to cope with high levels of external Mg 2+ . We show that the yeast genome (as well as other fungal genomes) harbour a single ACDP homologue, referred to as MAM3, that functions specifically in vacuolar Mg 2+ accumulation and is essential for tolerance to high Mg. In parallel, vacuolar ACDP homologues were identified from Arabidopsis and shown to complement the yeast mutant mam3Δ . An Arabidopsis mutant lacking one of the vacuolar ACDP homologues displayed hypersensitivity to high-Mg conditions and accumulated less Mg in the vacuole compared with the wild type. Taken together, our results suggest that conserved transporters mediate vacuolar Mg 2+ sequestration in fungal and plant cells to maintain cellular Mg 2+ homeostasis in response to fluctuating Mg 2+ levels in the environment.