In addition, a 22-amino acid sequence (flg22) of the conserved N-terminal part of flagellin is known to activate plant defence mechanisms.[6] Flagellin perception in Arabidopsis thaliana functions via the receptor-like-kinase FLS2 (flagellin-sensitive-2)). Upon flg22 detection, FLS2 quickly binds to BAK1 (BRI1-associated kinase 1) to initiate signalling by reciprocal transphosporylation of their kinase domains.[7] Mitogen-activated-protein-kinases (MAPK) acts as downstream signalling compounds, leading ultimately to PAMP-triggered immunity in which more than 900 genes are up-/down-regulated upon flg22 treatment.