CHARACTERIZATION AND MUTATIONAL ANALYSIS OF NODHPQ GENES OF RHIZOBIUMSP., STRAIN N33

We have shown, by sequencing the nodulation gene region of Rhizobium s p. strain N33 previously isolated from the Canadian high arctic, that the nodHPQ genes are located in a 4.8-kb region downstream of nodBCIJ. The open reading frames of nodHPQ are 747, 906, and 1941 nucleotides long, respectively. The strain N33 genome contains one copy of nodH an d two copies of nodPQ that are homologous to those genes in Rhizobium meliloti. Tn5 insertions in the nodHPQ genes of strain N33 did not aff ect the formation of nodules on the two homologous hosts, Astragalus c icer and Onobrychis viciifolia. Since strain N33 contains the nodBCIJH PQ genes and the recently sequenced nodAFEG genes, we looked for simil ar host range with R. meliloti. Strain N33 and R. meliloti strains A2 and RCR2011 were shown to induce the formation of root nodules on plan ts of O. viciifolia. However, strain N33, compared with R. meliloti st rains, was able to elicit a few, white, empty, root nodules on Medicag o sativa. R. meliloti strains, compared with strain N33, were shown to induce only few nodules containing bacteria on A, cicer, Induction of nod genes transcription in strain N33 was shown to be induced by a va riety of flavonoid compounds that are different from those inducing no d genes from R. meliloti.