title: A genetic screen for mutants defective in IAA1-LUC degradation in Arabidopsis thaliana reveals an important requirement for TOPOISOMERASE6B in auxin physiology.
abstract: Many plant growth and developmental processes are modulated by the hormone auxin. Auxin-modulated proteolysis of Aux/IAAs, a family of transcriptional repressors, represents a major mode of auxin action. Auxin facilitates the interaction of Aux/IAAs with TIR1/AFB F-box proteins, promoting their ubiquitination by the SCF(TIR1/AFB) ubiquitin E3 ligase leading to subsequent degradation by the 26S proteasome. To identify new genes regulating Aux/IAA proteolysis in Arabidopsis thaliana, we took a genetic approach, identifying individuals with altered degradation of an IAA1-luciferase fusion protein (IAA1-LUC). A mutant with 2-fold slower IAA1-LUC degradation rate compared with wild-type was isolated. Positional cloning identified the mutant as an allele of TOPOISOMERASE6B, named top6b-7. TOP6B encodes a subunit of a plant and archea-specific enzyme regulating endoreduplication, DNA damage repair and transcription in plants. T-DNA insertion alleles (top6b-8 and top6b-9) were also analyzed. top6b-7 seedlings are less sensitive to exogenous auxin than wild-type siblings in primary root growth assays, and experiments with DR5:GUS. Additionally, top6b-7 seedlings have a 40% reduction in the amount of endogenous IAA. These data suggest that increased IAA1-LUC half-life in top6b-7 probably results from a combination of both lower endogenous IAA levels and reduced sensitivity to auxin.
authors.affiliation: a Department of Molecular and Cellular Biology and Plant Biology Graduate Group ; University of California ; Davis , CA USA.
authors.forename: Jonathan
authors.initials: J
authors.lastname: Gilkerson
authors.forename: Judy
authors.initials: J
authors.lastname: Callis
mesh_terms: D000483:Alleles; D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000201:enzymology / Q000235:genetics / Q000254:growth & development / Q000502:physiology*; D029681:Arabidopsis Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D001483:Base Sequence; D002874:Chromosome Mapping; D004269:DNA, Bacterial / Q000235:genetics; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D005820:Genetic Testing; D005966:Glucuronidase / Q000378:metabolism; D007210:Indoleacetic Acids / Q000378:metabolism*; D008156:Luciferases / Q000378:metabolism; D008969:Molecular Sequence Data; D016254:Mutagenesis, Insertional / Q000235:genetics; D009154:Mutation / Q000235:genetics*; D009687:Nuclear Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D010641:Phenotype; D018517:Plant Roots / Q000254:growth & development; D059748:Proteolysis; D011993:Recombinant Fusion Proteins
chemical_list: D029681:Arabidopsis Proteins; D004269:DNA, Bacterial; D004268:DNA-Binding Proteins; C491592:IAA1 protein, Arabidopsis; D007210:Indoleacetic Acids; D009687:Nuclear Proteins; D011993:Recombinant Fusion Proteins; C036483:T-DNA; D008156:Luciferases; D005966:Glucuronidase
keywords: 2, 4-D, 2, 4-dichlorophenoxyacetic acid; Arabidopsis thaliana; Aux/IAA; DR5:GUS; IAA, indole-3-acetic acid; IAA1-LUC, IAA1-luciferase fusion protein; LUC, luciferase; TOPOISOMERASE6B; UPS, ubiquitin proteasome system; auxin; indole-3-acetic acid; luciferase fusions; protein degradation; top6b, TOPOISOMERASE6B