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Defects in flagellin glycosylation affect the virulence of Pseudomonas syringae pv. tabaci 6605

¹ Okayama University;
² National Food Research Institute;
³ Forestry and Forest Products Research Institute

Flagellar motility and its glycosylation are indispensable for the virulence of Pseudomonas syringae pv. tabaci 6605. Six serine residues of flagellin protein at positions 143, 164, 176, 183, 193, and 201 are glycosylated, and the glycan structure at 201 was determined to consist of a trisaccharide of two L-rhamnosyl residues and a modified 4-amino-4,6-dideoxyglucosyl (viosamine) residue. To investigate the glycan structures attached to the other serine residues and to identify the important glycans for virulence, Ser/Ala-substituted mutants were generated. Six mutant strains that each retained a single glycosylated serine residue were generated by replacing five of the six serine residues with alanine residues. Matrix-assisted laser desorption/ionization time of flight (MALDI-TOF) mass analysis of flagellin proteins revealed that the major composition of each glycan was a trisaccharide basically similar to that at position 201, but with heterogeneity in glycoform distribution. Swarming motility and amounts of acyl homoserine lactones (AHLs) as quorum-sensing signal molecules were significantly reduced, especially in the S143-5S/A and S201-5S/A mutants, whereas tolerance to antibiotics was increased in these two mutants. All the mutants showed lower ability to cause disease on host tobacco plants. These results supported our previous finding that the glycosylation of the sites located on the most external surface, such as S176 and S183, are required for virulence in P. syringae pv. tabaci 6605. Furthermore, it is speculated that flagellum-dependent motility might be correlated with quorum sensing and antibiotic resistance.

⁴ E-mail: yuki{at}cc.okayama-u.ac.jp