Involved in plant defense against Phytophtora parasitica (PubMed:28082413). Contributes positively to Nicotiana resistance against P.parasitica (PubMed:28082413). Binds the P.parasitica xyloglucanase XEG1 and inhibits its cell wall degrading enzyme activity and its contribution as P.parasitica virulence factor (PubMed:28082413). XEG1 acts as an important virulence factor during P.parasitica infection but also acts as a pathogen-associated molecular pattern (PAMP) in Nictotiana species, where it can trigger defense responses including cell death (PubMed:28082413). (Microbial infection) Possesses stronger binding affinity with XLP1, a truncated paralog of P.parasitica XEG1 which has no enzyme activity. Is impaired in its inhibitor activity towards the P.parasitica xyloglucanase XEG1 when hijacked by XLP1 binding. Interacts with the Phytophtora parasitica xyloglucanase XEG1 and xyloglucanase-like XLP1 (PubMed:28082413). Possesses stronger binding affinity with XLP1, a truncated paralog of P.parasitica XEG1 which has no enzyme activity (PubMed:28082413). Belongs to the peptidase A1 family.