The best-characterized PAMP(pathogen-associated molecular pattern) known to activate innate immunity in plants is flagellin from Pseudomonas bacteria. A conserved N-terminal peptide of flagellin, flg22, is a potent elicitor of defense responses in tomato and Arabidopsis. In Arabidopsis, flg22 is perceived by FLS2, a receptor-like kinase that activates downstream events through a MAP kinase cascade. Pretreatment of Arabidopsis with flg22 peptide not only globally induces defense gene expression, but also protects plants from subsequent infection of the virulent DC3000.
Li X, Lin H, Zhang W, Zou Y, Zhang J, Tang X, Zhou JM. Flagellin induces innate immunity in nonhost interactions that is suppressed by Pseudomonas syringae effectors. Proc Natl Acad Sci U S A. 2005 Sep 6;102(36):12990-5. doi: 10.1073/pnas.0502425102. Epub 2005 Aug 25. PMID: 16123135; PMCID: PMC1200263.