title: Auxin and Tryptophan Homeostasis Are Facilitated by the ISS1/VAS1 Aromatic Aminotransferase in Arabidopsis.
abstract: Indole-3-acetic acid (IAA) plays a critical role in regulating numerous aspects of plant growth and development. While there is much genetic support for tryptophan-dependent (Trp-D) IAA synthesis pathways, there is little genetic evidence for tryptophan-independent (Trp-I) IAA synthesis pathways. Using Arabidopsis, we identified two mutant alleles of ISS1 ( I: ndole S: evere S: ensitive) that display indole-dependent IAA overproduction phenotypes including leaf epinasty and adventitious rooting. Stable isotope labeling showed that iss1, but not WT, uses primarily Trp-I IAA synthesis when grown on indole-supplemented medium. In contrast, both iss1 and WT use primarily Trp-D IAA synthesis when grown on unsupplemented medium. iss1 seedlings produce 8-fold higher levels of IAA when grown on indole and surprisingly have a 174-fold increase in Trp. These findings indicate that the iss1 mutant's increase in Trp-I IAA synthesis is due to a loss of Trp catabolism. ISS1 was identified as At1g80360, a predicted aromatic aminotransferase, and in vitro and in vivo analysis confirmed this activity. At1g80360 was previously shown to primarily carry out the conversion of indole-3-pyruvic acid to Trp as an IAA homeostatic mechanism in young seedlings. Our results suggest that in addition to this activity, in more mature plants ISS1 has a role in Trp catabolism and possibly in the metabolism of other aromatic amino acids. We postulate that this loss of Trp catabolism impacts the use of Trp-D and/or Trp-I IAA synthesis pathways.
authors.affiliation: Department of Biology, Boston University, Boston, Massachusetts 02215.
authors.forename: Michael
authors.initials: M
authors.lastname: Pieck
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Massachusetts, Amherst, Massachusetts 01003.
authors.forename: Youxi
authors.initials: Y
authors.lastname: Yuan
authors.affiliation: Department of Biology, Boston University, Boston, Massachusetts 02215.
authors.forename: Jason
authors.initials: J
authors.lastname: Godfrey
authors.affiliation: Department of Biology, Boston University, Boston, Massachusetts 02215.
authors.forename: Christopher
authors.initials: C
authors.lastname: Fisher
authors.affiliation: Department of Biology, Boston University, Boston, Massachusetts 02215.
authors.forename: Sanda
authors.initials: S
authors.lastname: Zolj
authors.affiliation: Department of Biology, Boston University, Boston, Massachusetts 02215.
authors.forename: Dylan
authors.initials: D
authors.lastname: Vaughan
authors.affiliation: Department of Biology, Boston University, Boston, Massachusetts 02215.
authors.forename: Nicholas
authors.initials: N
authors.lastname: Thomas
authors.affiliation: Department of Biology, Boston University, Boston, Massachusetts 02215.
authors.forename: Connie
authors.initials: C
authors.lastname: Wu
authors.affiliation: Department of Biology, Boston University, Boston, Massachusetts 02215.
authors.forename: Julian
authors.initials: J
authors.lastname: Ramos
authors.affiliation: Chemistry Instrumentation Center, Boston University, Boston, Massachusetts 02215.
authors.forename: Norman
authors.initials: N
authors.lastname: Lee
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Massachusetts, Amherst, Massachusetts 01003.
authors.forename: Jennifer
authors.initials: J
authors.lastname: Normanly
authors.affiliation: Department of Biology, Boston University, Boston, Massachusetts 02215 celenza@bu.edu.
authors.forename: John L
authors.initials: JL
authors.lastname: Celenza
mesh_terms: D017360:Arabidopsis / Q000201:enzymology / Q000235:genetics / Q000254:growth & development*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism; D053898:Biosynthetic Pathways; D018506:Gene Expression Regulation, Plant; D007210:Indoleacetic Acids / Q000378:metabolism*; D007211:Indoles / Q000494:pharmacology; D018515:Plant Leaves / Q000201:enzymology / Q000235:genetics / Q000254:growth & development; D036226:Seedlings / Q000201:enzymology / Q000235:genetics / Q000254:growth & development; D000637:Transaminases / Q000235:genetics / Q000378:metabolism*; D014364:Tryptophan / Q000378:metabolism*
chemical_list: D029681:Arabidopsis Proteins; D007210:Indoleacetic Acids; D007211:Indoles; C030374:indole; D014364:Tryptophan; D000637:Transaminases
keywords: Arabidopsis thaliana; ISS1/VAS1; auxin; phenylpropanoids; tryptophan metabolism