title: Brassinosteroid control of shoot gravitropism interacts with ethylene and depends on auxin signaling components.
abstract: OBJECTIVE
  To reach favorable conditions for photosynthesis, seedlings grow upward when deprived of light upon underground germination. To direct their growth, they use their negative gravitropic capacity. Negative gravitropism is under tight control of multiple hormones.
  
  
  METHODS
  By counting the number of standing plants in a population or by real time monitoring of the reorientation of gravistimulated seedlings of Arabidopsis thaliana, we evaluated the negative gravitropism of ethylene or brassinosteroid (BR) treated plants. Meta-analysis of transcriptomic data on AUX/IAA genes was gathered, and subsequent mutant analysis was performed.
  
  
  RESULTS
  Ethylene and BR have opposite effects in regulating shoot gravitropism. Lack of BR enhances gravitropic reorientation in 2-d-old seedlings, whereas ethylene does not. Lack of ethylene signaling results in enhanced BR sensitivity. Ethylene and BRs regulate overlapping sets of AUX/IAA genes. BRs regulate a wider range of auxin signaling components than ethylene.
  
  
  CONCLUSIONS
  Upward growth in seedlings depends strongly on the internal hormonal balance. Endogenous ethylene stimulates, whereas BRs reduce negative gravitropism in a manner that depends on the function of different, yet overlapping sets of auxin signaling components.
authors.affiliation: Laboratory of Functional Plant Biology, Department of Physiology, Ghent University, Karel Lodewijk Ledeganckstraat 35, B-9000 Gent, Belgium.
authors.forename: Filip
authors.initials: F
authors.lastname: Vandenbussche
authors.forename: Pieter
authors.initials: P
authors.lastname: Callebert
authors.forename: Petra
authors.initials: P
authors.lastname: Zadnikova
authors.forename: Eva
authors.initials: E
authors.lastname: Benkova
authors.forename: Dominique
authors.initials: D
authors.lastname: Van Der Straeten
mesh_terms: D017360:Arabidopsis / Q000187:drug effects / Q000235:genetics / Q000254:growth & development / Q000502:physiology*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism; D060406:Brassinosteroids / Q000494:pharmacology*; D003624:Darkness; D015536:Down-Regulation / Q000187:drug effects; D005030:Ethylenes / Q000494:pharmacology*; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D018522:Gravitropism / Q000187:drug effects*; D007210:Indoleacetic Acids / Q000378:metabolism*; D008954:Models, Biological; D018520:Plant Shoots / Q000187:drug effects / Q000502:physiology*; D036226:Seedlings / Q000187:drug effects / Q000235:genetics / Q000254:growth & development; D015398:Signal Transduction / Q000187:drug effects*; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism
chemical_list: C503426:ARF19 protein, Arabidopsis; C503425:ARF7 protein, Arabidopsis; D029681:Arabidopsis Proteins; D060406:Brassinosteroids; D005030:Ethylenes; D007210:Indoleacetic Acids; D014157:Transcription Factors; C036216:ethylene