Comparative Response of Pylaisiella selwynii to Agrobacterium and Rhizobium Species

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Abstract
Thirty-five strains of Agrobacterium and 5 strains of Rhizobium were tested for their ability to induce developmental changes in the moss P. selwynii. The avirulent A. radiobacter (7 strains) and nontumorigenic strains of A. tumefaciens (4 strains) had relatively little effect on moss development. Virulent strains of A. tumefaciens (17 strains), A. rubi (2 strains) and A. rhizogenes (5 strains) signficantly altered development of the moss. Bud formation was induced by most strains, and these developed into normal gametophores, abnormal gametophores or callus masses, depending on the strain of Agrobacterium. A. rhizogenes and 3 strains of A. tumefaciens induced formation of numerous rhizoid-like filaments and only occasional gametophores. All 5 spp. of Rhizobium tested induced bud formation and normal gametophore development. The most effective of these strains, R. leguminosarum C56, required contact between moss and bacterium, similar to that required by A. tumefaciens. This strain also competed with virulent A. tumefaciens for attachment sites on the moss filaments, suggesting Agrobacterium and Rhizobium adhere to the moss via similar bacterial wall components. The rhizoid-inducing substance produced by A. rhizogenes strain TR7 readily passed through filters separating bacterium and moss in a parabiotic chamber, indicating it is released into the medium by the bacterium. The correlation between higher plant infectivity and the ability to induce developmental changes in P. selwynii suggests this system may offer unique possibilities for the study of Agrobacterium and Rhizobium infectivity.

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