title: Arabidopsis gulliver1/SUPERROOT2-7 identifies a metabolic basis for auxin and brassinosteroid synergy.
abstract: Phytohormone homeostasis is essential for proper growth and development of plants. To understand the growth mechanisms mediated by hormonal levels, we isolated a gulliver1 (gul1) mutant that had tall stature in the presence of both brassinazole and the light. The gul1 phenotype depended on functional BR biosynthesis; the genetic introduction of dwarf4, a BR biosynthetic mutation, masked the long hypocotyl phenotype of gul1. Furthermore, BR biosynthesis was dramatically enhanced, such that the level of 22-hydroxy campesterol was 5.8-fold greater in gul1. Molecular cloning revealed that gul1 was a missense mutation, resulting in a glycine to arginine change at amino acid 116 in SUPERROOT2 (CYP83B1), which converts indole acetaldoxime to an S-alkyl thiohydroximate adduct in the indole glucosinolate pathway. Auxin metabolite profiling coupled with quantitative reverse transcription polymerase chain reaction (RT-PCR) analysis of auxin biosynthetic genes revealed that gul1/sur2-7 activated multiple alternative branches of tryptophan-dependent auxin biosynthetic pathways. Furthermore, exogenous treatment of gul1/sur2-7 with BRs caused adventitious roots from hypocotyls, indicative of an increased response to BRs relative to wild-type. Different from severe alleles of sur2, gul1/sur2-7 lacked 'high-auxin' phenotypes that include stunted growth and callus-like disintegration of hypocotyl tissues. The auxin level in gul1/sur2-7 was only 1.6-fold greater than in the wild-type, whereas it was 4.2-fold in a severe allele like sur2-8. Differences in auxin content may account for the range of phenotypes observed among the sur2 alleles. This unusual allele provides long-sought evidence for a synergistic interaction between auxin and BRs in promoting growth in Arabidopsis at the level of their biosynthetic enzymes.
authors.affiliation: School of Biological Sciences, College of Natural Sciences, Seoul National University, Seoul, 151-747, Korea.
authors.forename: Puna M
authors.initials: PM
authors.lastname: Maharjan
authors.forename: Brian P
authors.initials: BP
authors.lastname: Dilkes
authors.forename: Shozo
authors.initials: S
authors.lastname: Fujioka
authors.forename: Aleš
authors.initials: A
authors.lastname: Pěnčík
authors.forename: Karin
authors.initials: K
authors.lastname: Ljung
authors.forename: Meike
authors.initials: M
authors.lastname: Burow
authors.forename: Barbara A
authors.initials: BA
authors.lastname: Halkier
authors.forename: Sunghwa
authors.initials: S
authors.lastname: Choe
mesh_terms: D019943:Amino Acid Substitution; D017360:Arabidopsis / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D060406:Brassinosteroids / Q000378:metabolism* / Q000494:pharmacology; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics / Q000378:metabolism*; D018506:Gene Expression Regulation, Plant; D005961:Glucosinolates / Q000378:metabolism; D018546:Hypocotyl / Q000235:genetics / Q000254:growth & development; D007210:Indoleacetic Acids / Q000378:metabolism*; D009154:Mutation; D020125:Mutation, Missense; D010091:Oximes / Q000378:metabolism; D010641:Phenotype; D018517:Plant Roots / Q000235:genetics / Q000254:growth & development / Q000378:metabolism; D030821:Plants, Genetically Modified; D015398:Signal Transduction
chemical_list: C111451:AT3G50660 protein, Arabidopsis; D029681:Arabidopsis Proteins; D060406:Brassinosteroids; D005961:Glucosinolates; D007210:Indoleacetic Acids; D010091:Oximes; D003577:Cytochrome P-450 Enzyme System; C530432:cytochrome P-450 79B2 protein, Arabidopsis; C431937:CYP83B1 protein, Arabidopsis; C023728:acetaldehyde oxime
keywords: Arabidopsis thaliana; brassinazole; cytochrome P450; picloram; whole genome resequencing