title: Glucose conjugation of anthranilate by the Arabidopsis UGT74F2 glucosyltransferase is required for tryptophan mutant blue fluorescence.
abstract: Plant mutants with defects in intermediate enzymes of the tryptophan biosynthetic pathway often display a blue fluorescent phenotype. This phenotype results from the accumulation of the fluorescent tryptophan precursor anthranilate, the bulk of which is found in a glucose-conjugated form. To elucidate factors that control fluorescent tryptophan metabolites, we conducted a genetic screen for suppressors of blue fluorescence in the Arabidopsis trp1-100 mutant, which has a defect in the second enzymatic step of the tryptophan pathway. This screen yielded loss-of-function mutations in the UDP-glucosyltransferase gene UGT74F2. The bacterially expressed UGT74F2 enzyme catalyzed a conjugation reaction, with free anthranilate and UDP-glucose as substrates, that yielded the same fluorescent glucose ester compound as extracted from the trp1-100 mutant. These results indicate that sugar conjugation of anthranilate by UGT74F2 allows its stable accumulation in plant tissues. A highly related Arabidopsis enzyme UGT74F1 could also catalyze this reaction in vitro and could complement the ugt74F2 mutation when overexpressed in vivo. However, the UGT74F1 gene is expressed at a lower level than the UGT74F2 gene. Therefore, even though UGT74F1 and UGT74F2 have redundant conjugating activities toward anthranilate, UGT74F2 is the major source of this activity in the plant.
authors.affiliation: Department of Biochemistry and Molecular Biology, the Bloomberg School of Public Health, The Johns Hopkins University, Baltimore, Maryland 21205, USA.
authors.forename: Juan A
authors.initials: JA
authors.lastname: Quiel
authors.forename: Judith
authors.initials: J
authors.lastname: Bender
mesh_terms: D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000201:enzymology* / Q000235:genetics; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D001483:Base Sequence; D003001:Cloning, Molecular; D017931:DNA Primers; D017343:Genes, Plant; D005838:Genotype; D005947:Glucose / Q000378:metabolism*; D005964:Glucosyltransferases / Q000235:genetics* / Q000378:metabolism*; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D016133:Polymerase Chain Reaction; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D013050:Spectrometry, Fluorescence / Q000379:methods; D014364:Tryptophan; D062367:ortho-Aminobenzoates / Q000378:metabolism*
chemical_list: D029681:Arabidopsis Proteins; D017931:DNA Primers; D005947:Glucose; D005964:Glucosyltransferases; D011994:Recombinant Proteins; D014364:Tryptophan; D062367:ortho-Aminobenzoates; C031385:anthranilic acid; C515668:SGT1 protein, Arabidopsis