The interactions between bacteria and their host plants are highly complex. Bacteria, whether beneficial or pathogenic, can be recognized by plants and elicit a defense response. Bacteria, in turn, must employ mechanisms to dampen the defense response. For many Gram-negative, plant-associated bacteria, collections of proteins called type III effectors are deployed directly into host cells via a type III secretion system, to interfere with plant defenses. My research uses molecular, genetic, genomic, and computational methods to study both symbiont and plant host. We are characterizing type III effectors of mutualists and pathogens. We also study the virulence- and defense-signaling network of plant pathogens and hosts, respectively.