title: Ethylene-induced Arabidopsis hypocotyl elongation is dependent on but not mediated by gibberellins.
abstract: Ethylene, or its precursor 1-aminocyclopropane-1-carboxylic acid (ACC), can stimulate hypocotyl elongation in the light. It is questioned whether gibberellins (GAs) play a role in this response. Tests with light of different wavelengths demonstrated that the ethylene response depends on blue light and functional cryptochrome signalling. Levels of bio-active GA(4) were reduced in seedlings showing an ethylene response. Furthermore, ACC treatment of seedlings caused accumulation of the DELLA protein RGA, a repressor of growth. Concurrently, transcript levels of several GA biosynthesis genes were up-regulated and GA inactivation genes down-regulated by ACC. Hypocotyl elongation in response to ACC was strongly reduced in seedlings with a diminished GA signal, while being vigorously stimulated in a quadruple DELLA knock-out mutant with constitutive GA signalling. These data show that ethylene-driven hypocotyl elongation is mainly blue light-dependent and that this ethylene response, although GA dependent, hence needing a basal GA level, is not mediated by GA, but rather acts via a separate pathway.
authors.affiliation: Unit of Plant Hormone Signaling & Bio-imaging, Department of Molecular Genetics, Ghent University, Ledeganckstraat 35, B-9000 Ghent, Belgium.
authors.forename: Filip
authors.initials: F
authors.lastname: Vandenbussche
authors.forename: Bram
authors.initials: B
authors.lastname: Vancompernolle
authors.forename: Ivo
authors.initials: I
authors.lastname: Rieu
authors.forename: Margaret
authors.initials: M
authors.lastname: Ahmad
authors.forename: Andy
authors.initials: A
authors.lastname: Phillips
authors.forename: Thomas
authors.initials: T
authors.lastname: Moritz
authors.forename: Peter
authors.initials: P
authors.lastname: Hedden
authors.forename: Dominique
authors.initials: D
authors.lastname: Van Der Straeten
mesh_terms: D017360:Arabidopsis / Q000254:growth & development* / Q000378:metabolism; D029681:Arabidopsis Proteins; D056931:Cryptochromes; D005030:Ethylenes / Q000378:metabolism*; D005420:Flavoproteins / Q000378:metabolism; D005875:Gibberellins / Q000096:biosynthesis*; D018546:Hypocotyl / Q000254:growth & development* / Q000378:metabolism; D008027:Light; D010940:Plant Proteins / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology
chemical_list: D029681:Arabidopsis Proteins; C538962:CRY1 protein, Arabidopsis; D056931:Cryptochromes; D005030:Ethylenes; D005420:Flavoproteins; D005875:Gibberellins; D010940:Plant Proteins; C036216:ethylene; C007842:gibberellic acid