Conserved Nodulation Genes in Rhizobium meliloti and Rhizobium trifolii.

Plasmids which contained wild-type or mutated Rhizobium meliloti nodulation (nod) genes were introduced into NodR. trifolii mutants ANU453 and ANU851 and tested for their ability to nodulate clover. Cloned wild-type and mutated R. meliloti nod gene segments restored ANU851 to Nod, with the exception of nodD mutants. Similarly, wild-type and mutant R. meliloti nod genes complemented ANU453 to Nod, except for nodCII mutants. Thus, ANU851 identifies the equivalent of the R. meliloti nodD genes, and ANU453 specifies the equivalent of the R. meliloti nodCII genes. In addition, cloned wild-type R. trifolii nod genes were introduced into seven R. meliloti Nod mutants. All seven mutants were restored to Nod on alfalfa. Our results indicate that these genes represent common nodulation functions and argue for an allelic relationship between nod genes in R. meliloti and R. trifolii.