Understanding the Host-Pathogen-Interface to Create Novel Resistance against Haustorium-Forming Pathogens

Many fungal and oomycete pathogens invade plants with a specialized infection structure named the haustorium for deriving nutrients from the host cell and cause serious diseases; in response plants have evolved elaborate defense mechanisms to fight against infection. Mechanisms of host-pathogen recognition and defense signaling have been extensively studied, however very little is known about the molecular warfare at the host-pathogen interface—the extra-haustorial membrane (EHM). We recently found that the Arabidopsis broad-spectrum resistance protein RPW8 and its family members are specifically targeted to the EHM encasing the haustorium of powdery mildew whereby RPW8 activates a defense strategy that concomitantly enhances the encasement of the haustorial complex and onsite accumulation of H₂O₂ to constrain the haustorium. Through a large scale mutational analysis, we have identified important residues in RPW8 that control its defense activity and two short motifs critical for its EHM-targeting. We are also using RPW8 as a probe to investigate the origin and biogenesis of the enigmatic EHM,  and as a delivery vehicle to target antimicrobial cargo proteins to the host-pathogen interface for engineering novel resistance against haustorium-forming pathogens. Recent research progress along these lines will be discussed.