Haiman Ge

Nutrient antagonism typically refers to the fact that too high a concentration of one nutrient inhibits the absorption of another nutrient. In plants, Ca²⁺ (Calcium) and Mg²⁺ (Magnesium) are the two most abundant divalent cations, which are known to have antagonistic interactions. Hence, maintaining their homeostasis is crucial for plant growth and development. In this study, we showed that MTP10 (Metal Tolerance Protein 10) is an important regulator for maintaining homeostasis of Mg and Ca in Arabidopsis. The mtp10 mutant displayed severe growth retardation in the presence of excess Mg²⁺, to which the addition of Ca²⁺ was able to rescue the phenotype of mtp10 mutant. Additionally, the deficiency of Ca²⁺ in the culture medium accelerated the high-Mg sensitivity of the mtp10 mutant. The yeast complementation assay suggested that AtMTP10 had no Ca²⁺ transport activity. And the ICP-MS data further confirmed the antagonistic relationship between Ca²⁺ and Mg²⁺, with the addition of Ca²⁺ reducing the excessive accumulation of Mg²⁺ and high-Mg inhibiting the uptake of Ca²⁺. We conclude that the Arabidopsis MTP10 is essential for the regulation of Mg and Ca homeostasis.

Magnesium (Mg²⁺) is an essential metal for plant growth; however, its over‐accumulation in cells can be cytotoxic. The metal tolerance protein family (MTP) belongs to an ubiquitous family of cation diffusion facilitator (CDF) proteins that export divalent metal cations for metal homeostasis and tolerance in all organisms. We describe here the identification of MTP10 to be critical for xylem Mg homeostasis in Arabidopsis under high Mg²⁺ conditions. The Arabidopsis plant contains 12 MTP genes, and only knockout of MTP10 decreased the tolerance of high‐Mg stress. The functional complementation assays in a Mg²⁺ ‐uptake‐deficient bacterial strain MM281 confirmed that MTP10 conducted Mg²⁺ transport. MTP10 is localized to the plasma membrane of parenchyma cells around the xylem. Reciprocal grafting analysis further demonstrated that MTP10 functions in the shoot to determine the shoot growth phenotypes under high Mg²⁺ conditions. Moreover, compared to the wild type, the mtp10 mutant accumulated more Mg²⁺ in xylem sap under high‐Mg stress. This study reveals that MTP10 facilitates Mg²⁺ diffusion from the xylem to shoots and thus determines Mg homeostasis in shoot vascular tissues during high‐Mg stress.