Journal Article

Auxin, Ethylene and Brassinosteroids: Tripartite Control of Growth in the <i>Arabidopsis</i> Hypocotyl

Liesbeth De Grauwe, Filip Vandenbussche, Olaf Tietz, Klaus Palme and Dominique Van Der Straeten

in Plant and Cell Physiology

Published on behalf of Japanese Society of Plant Physiologists

Volume 46, issue 6, pages 827-836
Published in print June 2005 | ISSN: 0032-0781
Published online June 2005 | e-ISSN: 1471-9053 | DOI: http://dx.doi.org/10.1093/pcp/pci111
Auxin, Ethylene and Brassinosteroids: Tripartite Control of Growth in the Arabidopsis Hypocotyl

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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.

Keywords: Adventitious roots; Apical hook; Auxin; Brassinosteroids; Ethylene; Hypocotyl elongation; ACC, 1-aminocyclopropane-1-carboxylic acid; alf, aberrant lateral root formation 1; amp, altered meristem program; BR, brassinosteroid; Brz2001, brassinazole; Cbb, cabbage; CLP, chloral lactophenol; cop, constitutive photomorphogenesis; cpd, constitutive photomorphogenesis and dwarfism; det, de-etiolated; EBR, epibrassinolide; hls, hookless; hpt, hauptling; GFP, green fluorescent protein; GUS, β-glucuronidase; LAX, like AUX1; LNM, low nutrient medium; NPA, α-naphthylphtalamic acid; PIN, pin-formed; pt, primordial timing; rty, rooty; sur, superroot; UCU, ultracurvata

Journal Article.  7178 words.  Illustrated.

Subjects: Biochemistry ; Molecular and Cell Biology ; Plant Sciences and Forestry

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