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The Cryptic Plasmid of Agrobacterium tumefaciens Cointegrates with the Ti Plasmid and Cooperates for Opine Degradation

July 1998 , Volume 11 , Number  7
Pages  583 - 591

Valérie Vaudequin-Dransart , 1 Annik Petit , 1 W. Scott Chilton , 2 and Yves Dessaux 1

1Institut des Sciences Végétales, CNRS UPR040, Avenue de la Terrasse, F-91198 Gif-sur-Yvette Cedex, France; 2Department of Botany, North Carolina State University, Raleigh 27695, U.S.A.

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Accepted 20 February 1998.

We crossed the Agrobacterium tumefaciens chrysanthemum strain ANT4, which harbors four plasmids, with the plasmid-free recipient C58.00RS. Transconjugants degrading the Amadori-opines chrysopine and deoxy-fructo-syl-oxo-proline (dfop) harbored the Ti plasmid of ANT4, termed pAtANT4b. Upon transfer to the recipient strain C58.00RS, pAtANT4b (pTiANT4) and pANT4a (the largest of the four plasmids of ANT4) could cointegrate. The cointegration of the two plasmids occurs at various places of the pTiANT4, a feature that may affect several functions of the Ti plasmid (e.g., opine degradation). Transcon-jugants utilizing the opine deoxy-fructosyl-glutamine (dfg) always harbored the large pAtANT4a. Other Agrobacterium strains, including nonpathogenic strains such as C58C1, naturally degraded dfg. Remarkably, strain C58C1 carries a large cryptic plasmid termed pAtC58 that also encodes dfg degradation. A screening of physiological traits additionally revealed that this plasmid allows utilization of octopine as sole nitrogen source after mutation. All these results demonstrate that the larger plasmid of A. tumefaciens is a catabolic plasmid and that both the “cryptic” plasmid and Ti plasmid cooperate for opine degradation.

Additional keywords: A. rhizogenes, conjugation, Ri plasmids.

© 1998 The American Phytopathological Society