Identification and Characterization of the nolYZ Genes of Bradyrhizobium japonicum. Thomas C. Dockendorff. (1) Center for Legume Research (2) Department of Microbiology M-409 Walters Life Science Building, The University of Tennessee, Knoxville 37996-0845 U.S.A. Arun J. Sharma, (1) and Gary Stacey(1,2). (1) Center for Legume Research (2) Department of Microbiology M-409 Walters Life Science Building, The University of Tennessee, Knoxville 37996-0845 U.S.A. MPMI 7:173-180. Accepted 2 November 1993. Copyright 1994 The American Phytopathological Society.

Characterization of an isoflavone-inducible locus closely linked to the common nod genes of Bradyrhizobium japonicum USDA110 led to the discovery of two open readinig frames, designated nolY and nolZ. These open reading frames are preceded by a sequence with strong similarity to a consensus NodD-binding site (nod box). Studies utilizing a nolZ'-'lacZ fusion indicated that inducible expression is dependent upon both NodDq and NodW, transcriptional regulators that are required for the expression of the common nodulation genes(e.g., nodYABC) of B. japonicum. A deletion mutation within nolY produced only slight defects in nodulation of soybeans, siratro, and cowpeas, but stronger defects were observed in nodulation of mung beans. An insertion mutation with nolZ showed no nodulation defects in the host plants tested. Competition assays for nodule occupancy in soybeans did not show any decrease it eh competitiveness of a nolY mutant, nor did a nolY mutant show any detectable alteration in the production of lipooligosaccharide nodulation signals.