Two magnesium transporters in the chloroplast inner envelope essential for thylakoid biogenesis in Arabidopsis

Summary Magnesium (Mg2+) serves as a cofactor for a number of photosynthetic enzymes in the chloroplast, and is the central atom of the Chl molecule. However, little is known about the molecular mechanism of Mg2+ transport across the chloroplast envelope. Here, we report the functional characterizat...

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Bibliographic Details
Published in:The New phytologist 2022-10, Vol.236 (2), p.464-478
Main Authors: Zhang, Bin, Zhang, Chi, Tang, Renjie, Zheng, Xiaojiang, Zhao, Fugeng, Fu, Aigen, Lan, Wenzhi, Luan, Sheng
Format: Article
Language:English
Subjects:
Albinism
Arabidopsis
Arabidopsis thaliana
Biogenesis
Biosynthesis
chloroplast development
Chloroplasts
Defects
embryogenesis
Embryos
Evolution
Genes
Magnesium
magnesium transport
Mutants
Mutation
Ovules
Photosynthesis
photosystem II
Protein transport
Proteins
Seedlings
thylakoid stacking
Transport
Uptake
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Summary:Summary Magnesium (Mg2+) serves as a cofactor for a number of photosynthetic enzymes in the chloroplast, and is the central atom of the Chl molecule. However, little is known about the molecular mechanism of Mg2+ transport across the chloroplast envelope. Here, we report the functional characterization of two transport proteins in Arabidopsis: Magnesium Release 8 (MGR8) and MGR9, of the ACDP/CNNM family, which is evolutionarily conserved across all lineages of living organisms. Both MGR8 and MGR9 genes were expressed ubiquitously, and their encoded proteins were localized in the inner envelope of chloroplasts. Mutations of MGR8 and MGR9 together, but neither of them alone, resulted in albino ovules and chlorotic seedlings. Further analysis revealed severe defects in thylakoid biogenesis and assembly of photosynthetic complexes in the double mutant. Both MGR8 and MGR9 functionally complemented the growth of the Salmonella typhimurium mutant strain MM281, which lacks Mg2+ uptake capacity. The embryonic and early seedling defects of the mgr8/mgr9 double mutant were rescued by the expression of MGR9 under the embryo‐specific ABI3 promoter. The partially rescued mutant plants were hypersensitive to Mg2+ deficient conditions and contained less Mg2+ in their chloroplasts than wild‐type plants. Taken together, we conclude that MGR8 and MGR9 serve as Mg2+ transporters and are responsible for chloroplast Mg2+ uptake.
ISSN:0028-646X
1469-8137
DOI:10.1111/nph.18349