Xanthomonas campestris pv campestris (Xcc) is a bacterial intravascular phytopathogen that is the causal agent of the black rot of crucifers. It has a broad host range that includes a majority of members of the Brassicaceae family. Whereas Xcc is widely considered to use hydathodes and wounds as preferential ways of entry into the leaf, it can also penetrate this organ through stomata (Buell, 2002). In Arabidopsis, Xcc 8004 can enter the leaf through both hydathodes and stomata, and the preferred route of entry depends both on the particular Arabidopsis ecotype and on environmental conditions (Hugouvieux et al., 1998). Because at least under some conditions and in certain ecotypes Xcc can enter Arabidopsis leaves through stomata, it is likely that Xcc possesses some mechanism to overcome stomatal defense.