Plant Molecular Biology

, Volume 27, Issue 6, pp 1071–1083 | Cite as

Transgene-mediated auxin overproduction in Arabidopsis: hypocotyl elongation phenotype and interactions with the hy6-1 hypocotyl elongation and axr1 auxin-resistant mutants

  • Charles P. Romano
  • Paul R. H. Robson
  • Harry Smith
  • Mark Estelle
  • Harry Klee
Research Article


Transgenic Arabidopsis thaliana plants constitutively expressing Agrobacterium tumefaciens tryptophan monooxygenase (iaaM) were obtained and characterized. Arabidopsis plants expressing iaaM have up to 4-fold higher levels of free indole-3-acetic acid (IAA) and display increased hypocotyl elongation in the light. This result clearly demonstrates that excess endogenous auxin can promote cell elongation in a whole plant. Interactions of the auxin-overproducing transgenic plants with the phytochrome-deficient hy6-1 and auxin-resistant axrl-3 mutations were also studied. The effects of auxin overproduction on hypocotyl elongation were not additive to the effects of phytochrome deficiency in the hy6-1 mutant, indicating that excess auxin does not counteract factors that limit hypocotyl elongation in hy6-1 seedlings. Auxin-overproducing seedlings are also qualitatively indistinguishable from wild-type controls in their response to red, far-red, and blue light treatments, demonstrating that the effect of excess auxin on hypocotyl elongation is independent of red and blue light-mediated effects. All phenotypic effects of iaaM-mediated auxin overproduction (i.e. increased hypocotyl elongation in the light, severe rosette leaf epinasty, and increased apical dominance) are suppressed by the auxin-resistant axr1-3 mutation. The axr1-3 mutation apparently blocks auxin signal transduction since it does not reduce auxin levels when combined with the auxin-overproducing transgene.

Key words

Arabidopsis transgenic plants auxin hypocotyl elongation photomorphogenesis 


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Copyright information

© Kluwer Academic Publishers 1995

Authors and Affiliations

  • Charles P. Romano
    • 1
  • Paul R. H. Robson
    • 2
  • Harry Smith
    • 2
  • Mark Estelle
    • 3
  • Harry Klee
    • 1
  1. 1.Monsanto Agricultural GroupSt. LouisUSA
  2. 2.Department of BotanyUniversity of LeicesterLeicesterUK
  3. 3.Department of BiologyIndiana UniversityBloomingtonUSA

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