Analysis of the Cell Surface of Pseudomonas syringae pv. glycinea with Monoclonal Antibodies. Vincent P. M. Wingate. Plant Biology Laboratory, Salk Institute for Biological Studies, La Jolla, CA 92037 U.S.A. Paul M. Norman, and Christopher J. Lamb. Plant Biology Laboratory, Salk Institute for Biological Studies, La Jolla, CA 92037 U.S.A. MPMI 3:408-416. Accepted 25 July 1990. Copyright 1990 The American Phytopathological Society.

Murine hybridoma cell lines were generated against the cell surface of pathogenically defined races of Pseudomonas syringae pv. glycinea, including race 4 strain A29-2 containing the race 6 avirulence gene avrA (race 4 strain A29-2*). Generation of a high number of hybridoma cell lines (20 to 40%) secreting antibodies was critically dependent upon the immunization schedule. Radioimmunoassay and western blot analysis identified monoclonal antibodies (Mabs) to race 4-specific epitopes and race 4 strain-specific epitopes that were not present on race 1 strain R1, race 5 strain R5, and race 6 strain R6. Similarly, certain other MAbs identified epitopes found on race 1 strain R1, race 5 strain R5, and race 6 strain R6 that were not present on race 4 strains. In contrast, Mabs were not found that discriminated between the cell surfaces of race 1 strain R1, race 5 strain R5, and race 6 strain R6. With few exceptions, protease-sensitive epitopes were common to all P. syringae pathovars, whereas the majority of periodate-sensitive epitopes were only present in P. s. pv. glycinea races and were not found in other P. syringae pathovars. There was no correlation between MAbs recognizing race-specific bacterial cell surface epitopes and the pattern of infectivity of the bacterial races on the soybean cultivars, save that the surface of race 4, which is virulent on a wide range of soybean cultivars, was immunologically very distinct from the other races examined, which are virulent on more limited sets of cultivars. Likewise no MAbs were identified that gave a pattern of race reactivity exclusively correlated with expression of the avrA gene. These data indicate that the bacterial cell surface may not have a direct role in the expression of avirulence. However, differences in bacterial epitopes at the genus, species, pathovar, race, and strain levels were identified by this approach, indicating that MAb technology is a useful tool for dissecting the cell surface of genetically related bacteria.