Isolation and Characterization of a Locus from Azospirillum brasilense Sp7That Complements theTumorigenic Defect of Agrobacterium tumefaciens chvB Mutant. Surabhi Raina. Genetic Engineering Unit, Centre for Biotechnology, Jawaharlal Nehru University, New Dehli-110 067, India. Ramesh Raina,T. V. Venkatesh, and H. K. Das Genetic Engineering Unit, Centre for Biotechnology, Jawaharlal Nehru University, New Dehli-110 067, India. MPMI 8:322-326. Accepted 5 December 1994. Copyright 1995 The American Phytopathological Society.

The chromosomal virulence gene chvB of Agrobacterium tumefaciens is required for pathogenesis. A DNA fragment from the chvB locus can hybridize to DNA from Azospirillum brasilense Sp7. This DNA fragment could restore the tumorigenic activity of the chvB mutant strain A. tumefaciens A1011 towards leaf disks of Nicotiana tabacum. An NH2-terminal open reading frame, 480 codons long, was most likely responsible for the restoration of the tumorigenic activity. The A. brasilense sequence showed good homology with the NH2-terminal region of the ndvB gene of Rhizobium meliloti.