title: An Arabidopsis basic helix-loop-helix leucine zipper protein modulates metal homeostasis and auxin conjugate responsiveness.
abstract: The plant hormone auxin can be regulated by formation and hydrolysis of amide-linked indole-3-acetic acid (IAA) conjugates. Here, we report the characterization of the dominant Arabidopsis iaa-leucine resistant3 (ilr3-1) mutant, which has reduced sensitivity to IAA-Leu and IAA-Phe, while retaining wild-type responses to free IAA. The gene defective in ilr3-1 encodes a basic helix-loop-helix leucine zipper protein, bHLH105, and the ilr3-1 lesion results in a truncated product. Overexpressing ilr3-1 in wild-type plants recapitulates certain ilr3-1 mutant phenotypes. In contrast, the loss-of-function ilr3-2 allele has increased IAA-Leu sensitivity compared to wild type, indicating that the ilr3-1 allele confers a gain of function. Microarray and quantitative real-time PCR analyses revealed five downregulated genes in ilr3-1, including three encoding putative membrane proteins similar to the yeast iron and manganese transporter Ccc1p. Transcript changes are accompanied by reciprocally misregulated metal accumulation in ilr3-1 and ilr3-2 mutants. Further, ilr3-1 seedlings are less sensitive than wild type to manganese, and auxin conjugate response phenotypes are dependent on exogenous metal concentration in ilr3 mutants. These data suggest a model in which the ILR3/bHLH105 transcription factor regulates expression of metal transporter genes, perhaps indirectly modulating IAA-conjugate hydrolysis by controlling the availability of metals previously shown to influence IAA-amino acid hydrolase protein activity.
authors.affiliation: Department of Biology, Harding University, Searcy, AR 72149, USA.
authors.forename: Rebekah A
authors.initials: RA
authors.lastname: Rampey
authors.forename: Andrew W
authors.initials: AW
authors.lastname: Woodward
authors.forename: Brianne N
authors.initials: BN
authors.lastname: Hobbs
authors.forename: Megan P
authors.initials: MP
authors.lastname: Tierney
authors.forename: Brett
authors.initials: B
authors.lastname: Lahner
authors.forename: David E
authors.initials: DE
authors.lastname: Salt
authors.forename: Bonnie
authors.initials: B
authors.lastname: Bartel
mesh_terms: D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D051792:Basic Helix-Loop-Helix Proteins / Q000235:genetics / Q000378:metabolism*; D003001:Cloning, Molecular; D015536:Down-Regulation; D018507:Gene Expression Regulation, Developmental; D018506:Gene Expression Regulation, Plant; D006706:Homeostasis; D007210:Indoleacetic Acids / Q000494:pharmacology*; D007501:Iron / Q000378:metabolism*; D016350:Leucine Zippers; D008345:Manganese / Q000378:metabolism*; D008969:Molecular Sequence Data; D009154:Mutation; D020411:Oligonucleotide Array Sequence Analysis; D010937:Plant Growth Regulators / Q000494:pharmacology*; D016133:Polymerase Chain Reaction; D036226:Seedlings / Q000737:chemistry; D017386:Sequence Homology, Amino Acid
chemical_list: D029681:Arabidopsis Proteins; D051792:Basic Helix-Loop-Helix Proteins; D007210:Indoleacetic Acids; D007501:Iron; D008345:Manganese; D010937:Plant Growth Regulators; C030737:indoleacetic acid