The rolB-like part of the Agrobacterium rhizogenes orf8 gene inhibits sucrose export in tobacco.
Many Agrobacterium T-DNA genes belong to the highly diverse rolB family. The mode of action of most of these genes is still unknown. rolB-like sequences also are present at the 5' ends of the T-DNA-located iaaM genes and the iaaM homolog orf8, whereas iaaM genes from Pseudomonas and Erwinia spp. lack such sequences. iaaM genes encode tryptophan monooxygenases; these enzymes convert tryptophan into indole-3-acetamide, a precursor of indole-3-acetic acid. Tobacco plants expressing the rolB-like part of the A4 orf8 gene (2x35S-A4-Norf8 plants) accumulate glucose, fructose, sucrose, and starch and resemble sucrose transporter (NtSUT1) antisense plants. Different lines of evidence indicate that 2x35S-A4-Norf8 plants export less sucrose from source leaves. Glucose, fructose, sucrose, and starch accumulate in source leaves during sink-source transition, whereas sink tissues like petioles and midveins contain lower levels than normal. Petiole exudation experiments demonstrate a significant decrease in export of label after 14C-sucrose infiltration and after 14CO2 labeling. Grafting of stunted homozygous 2x35S-A4-Norf8 plants onto wild-type rootstocks restores growth, indicating that unloading is not affected. Growth of 2x35S-A4-Norf8 seedlings is inhibited on naphthalene acetic acid-containing media, suggesting a link between sucrose transport and auxin sensitivity.
Umber
Marie
M
Institut de Biologie Moléculaire des Plantes, CNRS UPR2357, Strasbourg, France.
Voll
Lars
L
Weber
Andreas
A
Michler
Pierre
P
Otten
Léon
L
D001426:Bacterial Proteins / Q000235:genetics* / Q000502:physiology; D001692:Biological Transport / Q000235:genetics / Q000502:physiology; D002250:Carbon Radioisotopes; D005632:Fructose / Q000378:metabolism; D005947:Glucose / Q000378:metabolism; D009280:Naphthaleneacetic Acids / Q000494:pharmacology; D016366:Open Reading Frames / Q000235:genetics; D018515:Plant Leaves / Q000378:metabolism; D018517:Plant Roots / Q000187:drug effects / Q000254:growth & development / Q000378:metabolism; D030821:Plants, Genetically Modified; D013213:Starch / Q000378:metabolism; D013395:Sucrose / Q000378:metabolism*; D014026:Nicotiana / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D001617:beta-Glucosidase / Q000235:genetics* / Q000502:physiology
D001426:Bacterial Proteins; D002250:Carbon Radioisotopes; D009280:Naphthaleneacetic Acids; D005632:Fructose; D013395:Sucrose; D013213:Starch; C092241:RolB protein, Agrobacterium rhizogenes; D001617:beta-Glucosidase; D005947:Glucose