In plants, recognition of immunogenic molecular patterns, such as bacterial flagellin (flg22 epitope), leads to an enhanced state of immunity, designated pattern-triggered immunity (PTI). Following cognate ligand perception, pattern recognition receptors initiate sequential phosphorylation events to activate defense responses against invading pathogens. To gain further insight into PTI signaling, we conducted phosphoproteome analyses in Arabidopsis seedlings with immunogenic molecular patterns.