Deciphering the mechanism of antibiotic resistance associated with a plant ABC transporter

Abstract

ATP binding cassette (ABC) transporters are found in most organisms and typically function in the transport of substrates across membranes. Atwbc19 is an Arabidopsis ABC transporter protein that confers antibiotic resistance. Overexpression of Atwbc19 results in increased kanamycin resistance in plants, but the mechanism has not been established. Atwbc19 has an N‐terminal nucleotide binding domain and a transmembrane domain with six alpha helices and thus was assumed to function as a transporter. Four internal GFP fusion constructs were generated and introduced in Arabidopsis to examine the localization of Atwbc19. However, Atwbc19 could not be localized to a membrane compartment. Instead, GFP fluorescence was observed in the nucleus and cytoplasm, suggesting cleavage of the N‐terminal soluble portion of the protein and subsequent nuclear localization. To generate an alternative hypothesis, we initiated the analysis of several highly conserved regions found in the protein sequence of Atwbc19. A yeast two hybrid screen was carried out using either the N‐terminal region or the linker region as baits to identify proteins interacting with Atwbc19. Two proteins identified in the yeast two hybrid screen are a Eukaryotic Initiation Factor 3 subunit and Casein Kinase 2. Our results suggest that Atwbc19 may not function as a transporter but as a translation regulator.