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Poster

Session: Session 1 Presenting Authors at Posters (Odds)

P-423 - Microscopic analysis of the mechanisms of the initial attachment of rhizobia to the plant surface

Monday, July 14, 2025
13:30 - 15:15  
Location: Confex Hall 3
Symbiosis and Mutualism (mycorrhiza and N-fixing Rhizobia)
Rhizobia, a group of nitrogen-fixing bacteria, are known to form symbiotic nodules in leguminous plants. Thus, the initial physical attachment of bacteria to the plant roots is a critical step in this symbiotic interaction. A number of examples demonstrated that related bacteria attached to surfaces via single cellular pole using polar adhesins, such as unipolar polysaccharide (UPP). In this study, we focused on the initial attachment of Bradyrhizobium ottawaense SG09, a nitrogen-fixing rhizobium that has high N2O reducing activity, to the plant roots. Our microscopic analysis of fluorescent-tagged B. ottawaense SG09 revealed that the rhizobium attached to both the root surface and root hairs via a single cell pole. This unique attachment was observed not only in the natural host soybean, but also in the non-host plants, such as Arabidopsis, rice, corn, and wheat. We identified orthologous genes required for the production of UPP, namely uppC and uppE, in the genome of B. ottawaense SG09, and investigate the knock-out mutant strains of these genes in this process using A. thaliana. Our microscopic analysis revealed that both genes are, indeed, required for attachment to both the root surface and root hairs. Taken together, we established the in planta assay of rhizobial attachment using the model plant, which would open up a new avenue for further genetic dissection of the process.