Multiple Antibiotic Resistance in Arabidopsis Is Conferred by Mutations in a Chloroplast-Localized Transport Protein    

Abstract

Widespread antibiotic resistance is a major public health concern, and plants represent an emerging antibiotic exposure route. Recent studies indicate that crop plants fertilized with antibiotic-laden animal manure accumulate antibiotics; however, the molecular mechanisms of antibiotic entry and subcellular partitioning within plant cells remain unknown. Here, we report that mutations in the Arabidopsis (Arabidopsis thaliana) locus Multiple Antibiotic Resistance1 (MAR1) confer resistance, while MAR1 overexpression causes hypersensitivity to multiple aminoglycoside antibiotics. Additionally, yeast expressing MAR1 are hypersensitive to the aminoglycoside G418. MAR1 encodes a protein with 11 putative transmembrane domains with low similarity to ferroportin1 from Danio rerio. A MAR1:yellow fluorescent protein fusion localizes to the chloroplast, and chloroplasts from plants overexpressing MAR1 accumulate more of the aminoglycoside gentamicin, while mar1-1 mutant chloroplasts accumulate less than the wild type. MAR1 overexpression lines are slightly chlorotic, and chlorosis is rescued by exogenous iron. MAR1 expression is also down-regulated by low iron. These data suggest that MAR1 is a plastid transporter that is likely to be involved in cellular iron homeostasis and allows opportunistic entry of multiple antibiotics into the chloroplast.

Systems and Trans-System Level Analysis Identifies Conserved Iron Deficiency Responses in the Plant Lineage

“…Arabidopsis FPN2 is localized to vacuolar membranes and MAR1 to the plastid envelope membranes. The proteins can apparently transport divalent cations like Co 2+ and Ni 2+ , besides Fe 2+ (Schaaf et al, 2006;Conte et al, 2009;. Among the likely functions are provision of iron to the plastid or sequestration of other divalent cations to the vacuole.…”

The Arabidopsis YELLOW STRIPE LIKE4 and 6 Transporters Control Iron Release from the Chloroplast

“…Until now, the molecular mechanisms by which iron is transported into and out of the chloroplast remained elusive. Candidates for Fe import into the chloroplast include the permease PIC1, which might translocate proteins that are required for iron transport in the chloroplast (Duy et al, 2007(Duy et al, , 2011, the transporter MAR1/IREG3, which might transport an iron chelate or its ligand alone (Conte et al, 2009), or the ABC NAP14, which could be part of an iron transport complex (Shimoni-Shor et al, 2010). Our data provide strong evidence that the YSL4 and YSL6 transporters contribute to the export of iron from the chloroplast.…”

“…The chloroplastic transporter MAR1, a close homolog of the IREG/ Ferroportin efflux transporters, is also of interest. MAR1 expression is enhanced by Fe deficiency and its overexpression disrupts Fe homeostasis (Conte et al, 2009). MAR1 was proposed to transport an iron chelate or an iron ligand, such as nicotianamine (NA), in chloroplasts and to opportunistically take up aminoglycoside antibiotics.…”

Transcriptional Profiling of the Arabidopsis Iron Deficiency Response Reveals Conserved Transition Metal Homeostasis Networks

“…This gene, also known as MAR1, was shown to encode a Fe-regulated chloroplast envelope protein with putative roles in Fe homeostasis. Ectopic expression of IREG3 causes chlorosis, consistent with a function in Fe import (Conte et al, 2009). Although its precise function and localization are unknown, TAP1 might function in the export of Fe-S clusters from the plastid, similar to the ABC transporter STARIK in mitochondria, which has been linked to intracellular Fe homeostasis (Kushnir et al, 2001).…”