The T-DNA oncogene A4-orf8 from Agrobacterium rhizogenes A4 induces abnormal growth in tobacco.
The related orf8 and iaaM T-DNA genes from Agrobacterium are each composed of two distinct parts. The 5' parts (called Norf8 or NiaaM) encode a 200-amino-acid (aa) sequence with homology to various T-DNA oncoproteins such as RolB, RolC, and 6b. The 3' parts (Corf8 or CiaaM) encode a 550-aa sequence with homology to IaaM proteins from Pseudomonas and Pantoea spp. Whereas iaaM genes encode flavin adenine dinucleotide (FAD)-dependent tryptophan 2-monooxygenases that catalyze the synthesis of indole-3-acetamide (IAM), A4-orf8 from Agrobacterium rhizogenes A4 does not. Plants expressing a 2x35S-A4-Norf8 construct accumulate soluble sugars and starch. We now have regenerated plants that express the full-size 2x35S-A4-orf8 and the truncated 2x35S-A4-Corf8 gene. 2x35S-A4-Corf8 plants accumulate starch and show reduced growth like 2x35S-A4-Norf8 plants but, in addition, display a novel set of characteristic growth modifications. These consist of leaf hypertrophy and hyperplasia (blisters); thick, dark-green leaves; thick stems; and swollen midveins. Mutations in the putative FAD-binding site of A4-Orf8 did not affect the blister syndrome. Plants expressing 2x35S-A4-Corf8 had a normal phenotype but contained less starch and soluble sugars than did wild-type plants. When 2x35S-A4-Corf8 plants were crossed to starch-accumulating 2x35S-A4-Norf8 plants with reduced growth, A4-Corf8 partially restored growth and reduced starch accumulation. A4-Corf8xA4-Norf8 crosses did not lead to the blister syndrome, suggesting that this requires physical linkage of the A4-NOrf8 and A4-COrf8 sequences.
Umber
Marie
M
Institut de Biologie Moléculaire des Plantes, CNRS UPR2357, Rue du Géneral Zimmer 12, 67084 Strasbourg, France.
Clément
Bernadette
B
Otten
Léon
L
D001665:Binding Sites / Q000235:genetics; D003433:Crosses, Genetic; D004269:DNA, Bacterial / Q000235:genetics*; D005182:Flavin-Adenine Dinucleotide / Q000378:metabolism; D005798:Genes, Bacterial; D009154:Mutation; D016366:Open Reading Frames; D010641:Phenotype; D010935:Plant Diseases / Q000382:microbiology; D030821:Plants, Genetically Modified; D012231:Rhizobium / Q000235:genetics* / Q000378:metabolism / Q000472:pathogenicity*; D014026:Nicotiana / Q000254:growth & development / Q000382:microbiology*
D004269:DNA, Bacterial; C036483:T-DNA; D005182:Flavin-Adenine Dinucleotide