title: hydra Mutants of Arabidopsis are defective in sterol profiles and auxin and ethylene signaling.
abstract: The hydra mutants of Arabidopsis are characterized by a pleiotropic phenotype that shows defective embryonic and seedling cell patterning, morphogenesis, and root growth. We demonstrate that the HYDRA1 gene encodes a Delta8-Delta7 sterol isomerase, whereas HYDRA2 encodes a sterol C14 reductase, previously identified as the FACKEL gene product. Seedlings mutant for each gene are similarly defective in the concentrations of the three major Arabidopsis sterols. Promoter::reporter gene analysis showed misexpression of the auxin-regulated DR5 and ACS1 promoters and of the epidermal cell file-specific GL2 promoter in the mutants. The mutants exhibit enhanced responses to auxin. The phenotypes can be rescued partially by inhibition of auxin and ethylene signaling but not by exogenous sterols or brassinosteroids. We propose a model in which correct sterol profiles are required for regulated auxin and ethylene signaling through effects on membrane function.
authors.affiliation: Integrative Cell Biology Laboratory, School of Biological and Biomedical Sciences, University of Durham, South Road, Durham DH1 3LE, United Kingdom.
authors.forename: Martin
authors.initials: M
authors.lastname: Souter
authors.forename: Jennifer
authors.initials: J
authors.lastname: Topping
authors.forename: Margaret
authors.initials: M
authors.lastname: Pullen
authors.forename: Jiri
authors.initials: J
authors.lastname: Friml
authors.forename: Klaus
authors.initials: K
authors.lastname: Palme
authors.forename: Rachel
authors.initials: R
authors.lastname: Hackett
authors.forename: Don
authors.initials: D
authors.lastname: Grierson
authors.forename: Keith
authors.initials: K
authors.lastname: Lindsey
mesh_terms: D017360:Arabidopsis / Q000201:enzymology / Q000235:genetics* / Q000254:growth & development; D005030:Ethylenes / Q000494:pharmacology*; D007210:Indoleacetic Acids / Q000494:pharmacology*; D009154:Mutation; D010088:Oxidoreductases / Q000235:genetics* / Q000378:metabolism; D010641:Phenotype; D063245:Plant Development; D018517:Plant Roots / Q000187:drug effects / Q000235:genetics / Q000254:growth & development; D010944:Plants / Q000187:drug effects / Q000235:genetics; D015398:Signal Transduction / Q000235:genetics; D013251:Steroid Isomerases / Q000235:genetics* / Q000378:metabolism; D013261:Sterols / Q000378:metabolism*
chemical_list: D005030:Ethylenes; D007210:Indoleacetic Acids; D013261:Sterols; C036216:ethylene; D010088:Oxidoreductases; C022672:delta(14)-sterol reductase; D013251:Steroid Isomerases; C022669:delta(8)-delta(7)-sterol isomerase