ALT First communication events between host and pathogen: pathogen effectors (RxLR) are recognized by host R proteins leading to signal transduction activation, immune responses, and reactive oxygen species (ROS) release. ROS modulation is tightly controlled by the host peroxidases and purple acid phosphatase (PAP). Also, Plasmopara viticola is able to perceive host molecules activating signaling transduction pathways. Host cell wall alterations are promoted by the pathogen (serine proteases trypsin) and damage associated patterns (DAMPs) are generated and perceived by host FERONIA and β-xylosidase 5, leading also to an immune response activation. Secretion of oomycete cell wall (CW) degradation enzymes (e.g., 1,3-β-glucanases and GDSL esterase/lipase [GELP]) to the extracellular space is also promoted by the host as an attempt to arrest pathogen growth. Host proteins are represented in red; and pathogen proteins are represented in gray.