Transgene-mediated auxin overproduction in Arabidopsis: hypocotyl elongation phenotype and interactions with the hy6-1 hypocotyl elongation and axr1 auxin-resistant mutants.
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 axr1-3 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.
Romano
C P
CP
Monsanto Agricultural Group, St. Louis, MO 63198, USA.
Robson
P R
PR
Smith
H
H
Estelle
M
M
Klee
H
H
D017360:Arabidopsis / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism; D029681:Arabidopsis Proteins; D006133:Growth Substances; D018546:Hypocotyl / Q000235:genetics / Q000254:growth & development / Q000378:metabolism; D007210:Indoleacetic Acids / Q000096:biosynthesis* / Q000378:metabolism / Q000502:physiology; D008027:Light; D009154:Mutation; D010641:Phenotype; D010940:Plant Proteins / Q000235:genetics; D030821:Plants, Genetically Modified; D015398:Signal Transduction
C081977:AXR1 protein, Arabidopsis; D029681:Arabidopsis Proteins; D006133:Growth Substances; D007210:Indoleacetic Acids; D010940:Plant Proteins; C030737:indoleacetic acid