Functions in innate immunity. Functions as pattern recognition receptor (PRR), sensing bacterial peptidoglycan (PGN) and fungal chitin at the cell surface. Involved in resistance against the bacterial pathogen Xanthomonas oryzae pv. oryzae (Xoo) and the fungal pathogen Magnaporthe oryzae. Binds PGN and fungal chitin in vitro (PubMed:22872757). Involved in microbe-associated molecular patterns (MAMPs) perception and participates in the activation of defense genes against the bacterial pathogen Xanthomonas oryzae pv. oryzicola (Xoc) or the fungal pathogen Magnaporthe oryzae (PubMed:23299421). Interacts with LYP6 (PubMed:23299421). Interacts with CEBIP (PubMed:23299421, PubMed:24964058). Interacts with CERK1 (PubMed:24964058, PubMed:25335639). Expressed in roots and leaves. Induced by infection with the bacterial pathogen Xanthomonas oryzae pv. oryzae. Plants silencing LYP4 exhibit significant compromised defense responses and enhanced susceptibility toward the bacterial pathogen Xanthomonas oryzae and the fungal pathogen Magnaporthe oryzae.