Expression of Rhizobium galegae common nod clones in various backgrounds.

The cosmid clone pRg30, carrying common nodulation genes of Rhizobium galegae HAMBI 1174, and pRg33, a subclone of pRg30 that contains a 5.7-kb ClaI insert carrying nodDABC were conjugated into various Rhizobium nod- mutant strains and into a Ti plasmid-cured Agrobacterium tumefaciens. Complementation and expression of the nodABC genes of R. galegae were studied by following microscopically the infection process and the nodulation on different test plants. The nodABC genes of R. galegae complemented the nod- strains of other Rhizobium species. The presence of extra copies of common nod genes in the homologous R. galegae nodABC- strain induced an increased nodulation on Galega orientalis. However, the inserts of R. galegae in pRg30 and pRg33 do not carry sufficient genetic information for normal nodulation of test plants in an Agrobacterium background, because the Agrobacterium transconjugants induced root hair deformation on Galega plants, but no infection threads were detected and nodulelike structures developed only at low frequency. The Agrobacterium carrying the nodDABC of R. galegae did not cause the root hairs of Medigo sativa to deform.