Abstract
In plants, the hydroxymethylpyrimidine (HMP) and thiazole precursors of thiamin are synthesized and coupled together to form thiamin in plastids. Mutants unable to form HMP can be rescued by exogenous HMP, implying the presence of HMP transporters in the plasma membrane and plastids. Analysis of bacterial genomes revealed a transporter gene that is chromosomally clustered with thiamin biosynthesis and salvage genes. Its closest Arabidopsis homolog, the plastidic nucleobase transporter (PLUTO), is co-expressed with several thiamin biosynthetic enzymes. Heterologous expression of PLUTO in Escherichia coli or Saccharomyces cerevisiae increased sensitivity to a toxic HMP analog, and disrupting PLUTO in an HMP-requiring Arabidopsis line reduced root growth at low HMP concentrations. These data implicate PLUTO in plastidial transport and salvage of HMP.
Highlights
Thiamin diphosphate (ThDP) is an enzyme cofactor required by virtually all forms of life
We show that expression of this transporter in Escherichia coli or Saccharomyces cerevisiae increases sensitivity to a toxic HMP analog, and that knocking out this transporter in an HMP-requiring Arabidopsis mutant results in a root growth defect when the level of HMP supplied is lowered
Exploiting the fact that genes operating in the same pathway are often clustered on bacterial chromosomes [14], we used the SEED database and its tools [5] to search for uncharacterized transporter genes adjacent to known thiamin biosynthetic genes
Summary
Thiamin diphosphate (ThDP) is an enzyme cofactor required by virtually all forms of life. ThDP-dependent enzymes participate in crucial metabolic reactions that make or break C–C bonds. Fungi, and many prokaryotes synthesize thiamin de novo but it is an essential vitamin for animals. Thiamin is composed of hydroxyethylthiazole (HET) and hydroxymethylpyrimidine (HMP) moieties. These are synthesized separately as hydroxyethylthiazole monophosphate (HET-P) and hydroxymethylpyrimidine pyrophosphate (HMP-PP) and condensed to form thiamin monophosphate (ThMP) (Figure 1 ). The enzymes responsible for these reactions are found solely in the plastid [1]. The final conversion of ThMP to ThDP occurs in the cytosol [1,2,3]
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
