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Magnesium (Mg2+), an essential structural component of chlorophyll, is absorbed from the soil by roots and transported to shoots to support photosynthesis in plants. However, the molecular mechanisms underlying root-to-shoot Mg2+ translocation remain largely unknown. We describe here the identification of four plasma membrane (PM)-localized transporters, named Mg2+ release transporters (MGRs), that are critical for root-to-shoot Mg transport in Arabidopsis. Functional complementation assays in a Mg2+-uptake-deficient bacterial strain confirmed that these MGRs conduct Mg2+ transport. PM-localized MGRs (MGR4, MGR5, MGR6, and MGR7) were expressed primarily in root stellar cells and participated in the xylem loading step of the long-distance Mg2+ transport process. In particular, MGR4 and MGR6 played a major role in shoot Mg homeostasis, as their loss-of-function mutants were hypersensitive to low Mg2+ but tolerant to high Mg2+ conditions. Reciprocal grafting analysis further demonstrated that MGR4 functions in the root to determine shoot Mg2+ accumulation and physiological phenotypes caused by both low- and high-Mg2+ stress. Taken together, our study has identified the long-sought transporters responsible for root-to-shoot Mg2+ translocation in plants. Plants deliver Mg2+ to shoots, which is crucial for chloroplast structure and photosynthesis. In this study, the authors have identified four plasma membrane-localized Mg2+ release transporters (MGRs) that can load Mg2+ into the xylem and thus determine shoot Mg2+ accumulation in Arabidopsis. [ABSTRACT FROM AUTHOR]

Magnesium (Mg 2+ ), an essential structural component of chlorophyll, is absorbed from the soil by roots and transported to shoots to support photosynthesis in plants. However, the molecular mechanisms underlying root-to-shoot Mg 2+ translocation remain largely unknown. We describe here the identification of four plasma membrane (PM)-localized transporters, named Mg 2+ release transporters (MGRs), that are critical for root-to-shoot Mg transport in Arabidopsis. Functional complementation assays in a Mg 2+ -uptake-deficient bacterial strain confirmed that these MGRs conduct Mg 2+ transport. PM-localized MGRs (MGR4, MGR5, MGR6, and MGR7) were expressed primarily in root stellar cells and participated in the xylem loading step of the long-distance Mg 2+ transport process. In particular, MGR4 and MGR6 played a major role in shoot Mg homeostasis, as their loss-of-function mutants were hypersensitive to low Mg 2+ but tolerant to high Mg 2+ conditions. Reciprocal grafting analysis further demonstrated that MGR4 functions in the root to determine shoot Mg 2+ accumulation and physiological phenotypes caused by both low- and high-Mg 2+ stress. Taken together, our study has identified the long-sought transporters responsible for root-to-shoot Mg 2+  translocation in plants., (Copyright © 2022 The Author. Published by Elsevier Inc. All rights reserved.)