AtATM3 Is Involved in Heavy Metal Resistance in Arabidopsis

Abstract

AtATM3, an ATP-binding cassette transporter of Arabidopsis (Arabidopsis thaliana), is a mitochondrial protein involved in the biogenesis of iron-sulfur clusters and iron homeostasis in plants. Our gene expression analysis showed that AtATM3 is upregulated in roots of plants treated with cadmium [Cd(II)] or lead (II); hence, we investigated whether this gene is involved in heavy metal tolerance. We found that AtATM3-overexpressing plants were enhanced in resistance to Cd, whereas atatm3 mutant plants were more sensitive to Cd than their wild-type controls. Moreover, atatm3 mutant plants expressing 35S promoter-driven AtATM3 were more resistant to Cd than wild-type plants. Since previous reports often showed that the cytosolic glutathione level is positively correlated with heavy metal resistance, we measured nonprotein thiols (NPSH) in these mutant plants. Surprisingly, we found that atatm3 contained more NPSH than the wild type under normal conditions. AtATM3-overexpressing plants did not differ under normal conditions, but contained less NPSH than wild-type plants when exposed to Cd(II). These results suggest a role for AtATM3 in regulating cellular NPSH level, a hypothesis that was further supported by our gene expression study. Genetic or pharmacological inhibition of glutathione biosynthesis led to the elevated expression of AtATM3, whereas expression of the glutathione synthase gene GSH1 was increased under Cd(II) stress and in the atatm3 mutant. Because the closest homolog of AtATM3 in fission yeast (Schizosaccharomyces pombe), HMT1, is a vacuolar membrane-localized phytochelatin-Cd transporter, it is tempting to speculate that glutathione-Cd(II) complexes formed in the mitochondria are exported by AtATM3. In conclusion, our data show that AtATM3 contributes to Cd resistance and suggest that it may mediate transport of glutamine synthetaseconjugated Cd(II) across the mitochondrial membrane.

An Allelic Mutant Series of ATM3 Reveals Its Key Role in the Biogenesis of Cytosolic Iron-Sulfur Proteins in Arabidopsis

“…5D, bottom). The effect of cadmium observed by Kim et al (2006) in the atm3-1 mutant (C24 background) is also relatively weak (85% growth reduction in the mutant compared with 49% in the wild type) and very minor compared with that observed for mutants in the bona-fide cadmium extrusion pump AtPDR8 (Kim et al, 2007). These data suggest that ATM3 may play an indirect, rather than a direct, role in heavy metal resistance.…”

“…Following a report that the atm3-1 mutant roots showed a growth reduction in the presence of cadmium (Kim et al, 2006), the effect of cadmium on root length was tested for all atm3 alleles. Under our conditions, cadmium concentrations of 20 to 40 mM inhibited root growth in all atm3 alleles to a similar extent as in the wild type (Fig.…”

“…The atm3-1 (sta1) mutant is dwarfed and chlorotic, but the biochemical basis of its pleiotropic phenotypes is unknown. In addition, induced expression of ATM3 in response to cadmium and lead, as well as sensitivity of the atm3-1 (sta1) mutant to cadmium, have implicated the ATM3 transporter in heavy metal tolerance (Kim et al, 2006).…”

The Brassica juncea BjCdR15, an ortholog of Arabidopsis TGA3, is a regulator of cadmium uptake, transport and accumulation in shoots and confers cadmium tolerance in transgenic plants

“…Noticeably, BjCdR15 ⁄ TGA3 affect the expression of genes that play different roles as transporters: both AtPDR8 and AtHMA4 contribute to cadmium detoxification as cadmium extrusion pumps (Mills et al, 2005;Kim et al, 2007), whereas the characterization of AtNRAMP3 demonstrates its role in iron and cadmium transport and cadmium sensitivity, probably by driving cadmium efflux from the vacuole to the cytoplasm (Thomine et al, 2003). Experimental data have shown that the AtATM3 transporter has a mitochondrial localization, and is capable of contributing to heavy metal detoxification (Kim et al, 2006).…”

“…Genes belonging to different functional categories have been characterized in relation to their role in cadmium tolerance and accumulation. For instance, the ABC transporter ATM3 from Arabidopsis thaliana contributes to cadmium resistance and accumulation probably by mediating the transport of cadmium-glutathione conjugates across the mitochondrial membrane (Kim et al, 2006). The P 1B -type ATPase HMA4 plays a role in cadmium detoxification, being involved in its transport from root to shoot (Mills et al, 2003(Mills et al, , 2005Verret et al, 2004Verret et al, , 2005.…”