title: Auxin, ethylene and brassinosteroids: tripartite control of growth in the Arabidopsis hypocotyl.
abstract: Dark-grown Arabidopsis seedlings develop an apical hook by differential cell elongation and division, a process driven by cross-talk between multiple hormones. Auxins, ethylene and gibberellins interact in the formation of the apical hook. In the light, a similar complexity of hormonal regulation has been revealed at the level of hypocotyl elongation. Here, we describe the involvement of brassinosteroids (BRs) in auxin- and ethylene-controlled processes in the hypocotyls of both light- and dark-grown seedlings. We show that BR biosynthesis is necessary for the formation of an exaggerated apical hook and that either application of BRs or disruption of BR synthesis alters auxin response, presumably by affecting auxin transport, eventually resulting in the disappearance of the apical hook. Furthermore, we demonstrate that ethylene-stimulated hypocotyl elongation in the light is largely controlled by the same mechanisms as those governing formation of the apical hook in darkness. However, in the light, BRs appear to compensate for the insensitivity to ethylene in hls mutants, supporting a downstream action of BRs. Hence, our results indicate that HLS1, SUR1/HLS3/RTY1/ALF1 and AMP1/HPT/COP2/HLS2/PT act on the auxin-ethylene interaction, rather than at the level of BRs. A model for the tripartite hormone interactions is presented.
authors.affiliation: Unit Plant Hormone Signaling and Bio-imaging, Department of Molecular Genetics, Ghent University, Ledeganckstraat 35, B-9000 Gent, Belgium.
authors.forename: Liesbeth
authors.initials: L
authors.lastname: De Grauwe
authors.forename: Filip
authors.initials: F
authors.lastname: Vandenbussche
authors.forename: Olaf
authors.initials: O
authors.lastname: Tietz
authors.forename: Klaus
authors.initials: K
authors.lastname: Palme
authors.forename: Dominique
authors.initials: D
authors.lastname: Van Der Straeten
mesh_terms: D000598:Amino Acids, Cyclic / Q000494:pharmacology; D017360:Arabidopsis / Q000187:drug effects* / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D003624:Darkness; D005030:Ethylenes / Q000494:pharmacology*; D017343:Genes, Plant; D017930:Genes, Reporter; D018546:Hypocotyl / Q000187:drug effects / Q000254:growth & development / Q000378:metabolism / Q000528:radiation effects; D007210:Indoleacetic Acids / Q000235:genetics / Q000494:pharmacology*; D008027:Light; D008954:Models, Biological; D009154:Mutation; D010937:Plant Growth Regulators / Q000235:genetics / Q000378:metabolism* / Q000494:pharmacology*; D013256:Steroids / Q000378:metabolism*
chemical_list: D000598:Amino Acids, Cyclic; D005030:Ethylenes; D007210:Indoleacetic Acids; D010937:Plant Growth Regulators; D013256:Steroids; C023863:1-aminocyclopropane-1-carboxylic acid; C036216:ethylene