Conserved mechanism for vacuolar magnesium sequestration in yeast and plant cells

Magnesium (Mg²⁺) is an essential nutrient for all life forms. In fungal and plant cells, the majority of Mg²⁺ is stored in the vacuole but mechanisms for Mg²⁺ 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 Mg²⁺ sequestration that enables plant and yeast cells to cope with high levels of external Mg²⁺. 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 Mg²⁺ 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 Mg²⁺ sequestration in fungal and plant cells to maintain cellular Mg²⁺ homeostasis in response to fluctuating Mg²⁺ levels in the environment.