The Jasmonic Acid-Activated Signaling Cascade

The jasmonic acid (JA)-dependent defense program is repressed by JAZ-proteins which bind to the transcriptional activator MYC2. After pathogen attack or wounding, the JA derivative jasmonoyl-isoleucine (JA-Ile) accumulates and binds to the receptor protein COI1. Upon binding of JA-Ile to COI1, JAZ proteins become degraded through the 26S proteasome so that MYC2 is free to function (For review see Pauwels and Goossens, 2011). Consistent with this model, JAZ proteins are not degraded in coi1 and JA biosynthesis mutants leading to the permanent inactivation of the pathway. In the presence of the phytohormone ethylene, which is associated with pathogen attack rather than wounding, the cascade is modified (JA/ET cascade).