Conserved Nodulation Genes in Rhizobium meliloti and Rhizobium trifolii

Abstract

Plasmids which contained wild-type or mutated Rhizobium meliloti nodulation ( nod ) genes were introduced into Nod − R. 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 .