Deletion Analysis of the 5' Untranslated Region of the Rhizobium meliloti nodF Gene. Grant Kalinowski. Department of Biological Sciences, Stanford University, Stanford, CA 94305-5020 U.S.A. Sharon R. Long(1,2). (1) Howard Hughes Medical Institute and (2) Department of Biological Sciences, Stanford University, Stanford, CA 94305-5020 U.S.A. MPMI 9:869-873. Accepted 27 August 1996. Copyright 1996 The American Phytopathological Society.

Efficient establishment of the symbiosis between rhizobia and their host plants requires precise regulation of bacterial nod genes. The nod gene transcripts in Rhizobium meliloti have approximately 200 nucleotides of untranslated sequence 5' of the start codon (5' UTR). We measured the significance of this region by constructing fusions between deletion derivatives of nodF and the reporter ß-glucuronidase (GUS). Flavonoid-inducible expression of the fusions in R. meliloti was evident when extra copies of the positive transcriptional activators NodDl, NodD3, or SyrM were present. The fusions responded normally over a range of inducer concentrations in Rhizobium leguminosarum bv. trifolii. GUS assays in planta showed no significant difference between the deletion constructs and a wild-type fusion. We conclude that the 5' UTRs of the nod gene transcripts are unlikely to have a significant regulatory role.