Effector proteins of phytopathogenic bacteria: bifunctional signals in virulence and host recognition.

Phytopathogenic bacteria deliver effectors of disease into plant hosts via a Type III secretion system. These Type III effectors have genetically determined roles in virulence. They also are among the components recognized by the putative receptors of the plant innate immune system. Recent breakthroughs include localization of some of these Type III effectors to specific host cell compartments, and the first dissection of pathogenicity islands that carry them.