Xcc strains 8004 (wild type; Daniels et al., 1984), 8523 (rpfFTn5lac; Tang et al., 1991), and 8557 (rpfCpUIRM504; Slater et al., 2000) were grown in peptone, yeast, and malt extract medium (Cadmus et al., 1976). Escherichia coli DH5α were grown at 37°C in Luria-Bertani medium (Sambrook et al., 1989). Pst DC3000 and mutant derivatives were cultured at 28°C in Luria-Bertani medium supplemented with appropriate antibiotics. All strains were grown overnight with the appropriate antibiotics. Bacteria were collected by centrifugation and resuspended in 10:10 buffer. The final bacterial concentration for stomatal bioassays was 10⁸ cfu/mL for all strains. In coincubation experiments, 10⁸ cfu/mL of each strain were added to the incubation buffer.