title: The sax1 dwarf mutant of Arabidopsis thaliana shows altered sensitivity of growth responses to abscisic acid, auxin, gibberellins and ethylene and is partially rescued by exogenous brassinosteroid.
abstract: Genetic approaches using Arabidopsis thaliana aimed at the identification of mutations affecting events involved in auxin signalling have usually led to the isolation of auxin-resistant mutants. From a selection screen specifically developed to isolate auxin-hypersensitive mutants, one mutant line was selected for its increased sensitivity to auxin (x 2 to 3) for the root elongation response. The genetic analysis of sax1 (hypersensitive to abscisic acid and auxin) indicated that the mutant phenotype segregates as a single recessive Mendelian locus, mapping to the lower arm of chromosome 1. Sax1 seedlings grown in vitro showed a short curled primary root and small, round, dark-green cotyledons. In the greenhouse, adult sax1 plants were characterized by a dwarf phenotype, delayed development and reduced fertility. Further physiological characterization of sax1 seedlings revealed that the most striking trait was a large increase (x 40) in ABA-sensitivity of root elongation and, to a lesser extent, of ABA-induced stomatal closure; in other respects, hypocotyl elongation was resistant to gibberellins and ethylene. These alterations in hormone sensitivity in sax1 plants co-segregated with the dwarf phenotype suggesting that processes involved in cell elongation are modified. Treatment of mutant seedlings with an exogenous brassinosteroid partially rescued a wild-type size, suggesting that brassinosteroid biosynthesis might be affected in sax1 plants. Wild-type sensitivities to ABA, auxin and gibberellins were also restored in sax1 plants by exogenous application of brassinosteroid, illustrating the pivotal importance of the BR-related SAX1 gene.
authors.affiliation: Institut des Sciences Végétales, Centre National de la Recherche Scientifique, Gif sur Yvette, France. ephritikhine@isv.cnrs-gif.fr
authors.forename: G
authors.initials: G
authors.lastname: Ephritikhine
authors.forename: M
authors.initials: M
authors.lastname: Fellner
authors.forename: C
authors.initials: C
authors.lastname: Vannini
authors.forename: D
authors.initials: D
authors.lastname: Lapous
authors.forename: H
authors.initials: H
authors.lastname: Barbier-Brygoo
mesh_terms: D000040:Abscisic Acid / Q000494:pharmacology; D017360:Arabidopsis / Q000187:drug effects / Q000235:genetics* / Q000254:growth & development; D060406:Brassinosteroids; D002777:Cholestanols / Q000494:pharmacology; D002874:Chromosome Mapping; D005030:Ethylenes / Q000494:pharmacology; D017343:Genes, Plant; D005875:Gibberellins / Q000494:pharmacology; D007210:Indoleacetic Acids / Q000494:pharmacology; D009154:Mutation; D010641:Phenotype; D010937:Plant Growth Regulators / Q000494:pharmacology; D013260:Steroids, Heterocyclic / Q000494:pharmacology
chemical_list: D060406:Brassinosteroids; D002777:Cholestanols; D005030:Ethylenes; D005875:Gibberellins; D007210:Indoleacetic Acids; D010937:Plant Growth Regulators; D013260:Steroids, Heterocyclic; D000040:Abscisic Acid; C036216:ethylene; C023623:brassinolide