ISOLATION AND CHARACTERIZATION OF A LOCUS FROM AZOSPIRILLUM-BRASILENSE SP7 THAT COMPLEMENTS THE TUMORIGENIC DEFECT OF AGROBACTERIUM-TUMEFACIENS CHVB MUTANT

The chromosomal virulence gene chvB of Agrobacterium tumefaciens is re quired for pathogenesis. A DNA fragment from the chvB locus can hybrid ize to DNA from Azospirillum hm brasilense Sp7. This DNA fragment coul d restore the tumorigenic activity of the chvB mutant strain A. tumefa ciens A1011 towards leaf disks of Nicotiana tabacum. An NH2-terminal o pen reading frame, 480 codons long, was most likely responsible for th e restoration of the tumorigenic activity. The A. brasilense sequence showed good homology with the NH2-terminal region of the ndvB gene of Rhizobium meliloti.