Molecular secrets of bacterial type III effector proteins

Most Gram-negative phytopathogenic bacteria are thought to inject effector proteins into the plant cell via a type III secretion system that is essent ial for pathogenicity. Plant targets and the mode of action of type III eff ector proteins, which include avirulence (Avr) proteins, are largely unknow n. However, recent findings have shed light on the molecular mechanisms of Avr action. Here, we focus on two classes of Avr proteins (the AvrBs3 and A vrRxv/YopJ families) that have been suggested to act as transcription facto rs and proteases, respectively.