A member of a novel Arabidopsis thaliana gene family of candidate Mg²⁺ ion transporters complements a yeast mitochondrial group II intron‐splicing mutant

Abstract

Summary Autocatalytic activity of some group II introns has been demonstrated in vitro, but helper functions such as the yeast MRS2 protein are essential for splicing in vivo. In our search for such helper factors in plants, we pursued the cloning of two Arabidopsis thaliana homologues, atmrs2‐1 and atmrs2‐2. Atmrs2‐1, but not atmrs2‐2, complements the yeast deletion mutant of mrs2, and this is congruent with the prediction of two adjacent transmembrane stretches in AtMRS2‐1 and yeast MRS2 but not in AtMRS2‐2. This complementation depends on fusion of the native yeast mitochondrial import sequence to atmrs2‐1. A differing, non‐mitochondrial, cellular targeting in Arabidopsis is supported by the analysis of green fluorescent protein fusion constructs after transient transformation into plant protoplasts. Further members of what now appears to be a family of 10 mrs2 homologues are identified in the Arabidopsis genome. Similarity searches with the psi‐blast algorithm in the protein database fail to identify homologues of this novel gene family in any eukaryotes other than yeasts, but do identify its distant relatedness to the corA group of bacterial magnesium transporters. In line with this observation, intramitochondrial magnesium concentrations are indeed restored to wild‐type levels in the yeast mutant on complementation with atmrs2‐1.

Magnesium transporter AtMGT9 is essential for pollen development in Arabidopsis

“…In higher plants, CorA-like Mg 2+ transporter family (At-MGT) has been identified from Arabidopsis thaliana and consists of at least 10 members. Two of the family members, AtMGT1 and AtMGT10, were experimentally confirmed to function as high-affinity Mg 2+ transporters [12,13]. AtMGT5 was identified to function as a dual-functional Mg 2+ -transporter mediating both influx and efflux [22].…”

“…The At-MGT1 was localized in plant plasma membrane [12] and AtMGT10 (also known as AtMRS2-11) was localized in plant chloroplast envelope membrane system [21], implicating its role in Mg 2+ uptake and translocation into chloroplasts. A third member, AtMGT2 (also known as At-MRS2-1), complements the yeast deletion mutant mrs2 and restores the intramitochondrial Mg 2+ concentration to nearly wild-type level [13]. Very recently, Li et al [22] identified the fourth member AtMGT5, functioning as a dual-functional Mg 2+ -transporter that mediates uptake or efflux in a concentration-dependent manner.…”

“…Recently, crystal structure of the pentameric cone-shaped CorA Mg 2+ transporter from Thermotoga maritima had been elucidated by several research groups [15][16][17][18], demonstrating CorA as a channel-like transport system. npg Li et al [12] and Schock et al [13] independently identified a 10-member Arabidopsis AtMGT gene family encoding Mg 2+ transport proteins that are homologous to the bacterial CorA. Members of the AtMGT family are expressed in a broad range of plant tissues.…”

“…The CorA family of Mg 2+ transporters is the most extensively studied Mg 2+ transport system, which exists widely in bacteria, fungi, animals, and plants, mediating both influx and efflux of Mg 2+ , and appears to be the primary Mg 2+ transport system [10][11][12][13]. Topological analysis of CorA protein in bacteria reveals a unique structure that contains a large, acidic N-terminal domain and two transmembrane domains in the C-terminal region.…”

Fertility control: the role of magnesium transporters in pollen development

“…Higher plant transporters of the CorA/MRS2 family were first identified in 2000, when Schock et al [6] reported a gene family of ten members in Arabidopsis thaliana, named AtMRS2-1 to AtMRS2-10. These authors also demonstrated that AtMRS2-1 functionally complements Mrs2-deficient yeast restoring intramitochondrial Mg 2+ concentration to the wild-type level.…”