Abstract

Magnesium (Mg) is one of the essential nutrients for all living organisms. Plants acquire Mg from the environment and distribute within their bodies in the ionic form via Mg2+-permeable transporters. In Arabidopsis, the plasma membrane-localized magnesium transporter MGT6 mediates Mg2+ uptake under Mg-limited conditions, and therefore is important for the plant adaptation to low-Mg environment. In this study, we further assessed the physiological function of MGT6 using a knockout T-DNA insertional mutant allele. We found that MGT6 was required for normal plant growth during various developmental stages when the environmental Mg2+ was low. Interestingly, in addition to the hypersensitivity to Mg2+ limitation, mgt6 mutants displayed dramatic growth defects when external Mg2+ was in excess. Compared with wild-type plants, mgt6 mutants generally contained less Mg2+ under both low and high external Mg2+ conditions. Reciprocal grafting experiments further underpinned a role of MGT6 in a shoot-based mechanism for detoxifying excessive Mg2+ in the environment. Moreover, we found that mgt6 mgt7 double mutant showed more severe phenotypes compared with single mutants under both low- and high-Mg2+ stress conditions, suggesting that these two MGT-type transporters play an additive role in controlling plant Mg2+ homeostasis under a wide range of external Mg2+ concentrations.

Highlights

  • Magnesium (Mg) is an essential macronutrient for plants

  • We have shown that knock-down of MGT6 in transgenic plants by RNA interference resulted in growth retardation under low-Mg conditions (Mao et al, 2014)

  • RT-PCR analyses showed that full-length MGT6 transcript was not detectable in the mgt6 mutant, while MGT4 gene located in the same chromosome is normally expressed (Figure 1B)

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Summary

Introduction

Magnesium (Mg) is an essential macronutrient for plants. Being the most abundant free divalent cation in living cells, Mg2+ serves as a counter ion for nucleotides and a central metal for chlorophylls, and acts as a cofactor for many enzymes in catalytic processes. When the medium Mg2+ levels reached a moderate range (0.75, 1.25, and 3 mM), the growth of mgt6 mutants appeared comparable to that of wild-type (Figure 2A), primary root length or seedling fresh weight was slightly affected (Figures 2B,C).

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