Recent insights into the molecular mechanism of jasmonate signaling during insect-plant interaction

Abstract

Amongst all the phytohormones, jasmonates are most important signaling molecule associated with plant defense against herbivores as they activate the expression of both direct and indirect defenses. Jasmonates are produced at insect-infested local sites and either jasmonate itself or some Jasmonic Acid (JA)-elicited compound travels to systemic leaves and elicits defense response. Upon herbivory, receptors/sensors of the host plant recognize Herbivory Associated Molecular Patterns (HAMPs) and early signaling events start with the involvement of Mitogen Activated Protein Kinases (MAPKs). JA biosynthesis is initiated in the chloroplast with the hydrolysis of chloroplast membrane lipids by phospholipases releasing free α-linolenic acid (α-LA), which gets converted to 12-oxo-phytodienoic acid (OPDA). OPDA is subsequently transported to peroxisomes where JA is produced by β-oxidation and it conjugates with isoleucine by JA amino acid synthetase (JAR) enzymes. Once high levels of JA-Isoleucine (Ile) are achieved, JA-induced response is instigated by SCF complex (a complex consisting of Skp1, Cullin-1 and F-box protein). JA-Ile forms a complex to form JA-Ile-COI1 (Coronatine insensitive Protein1) that recognizes a target protein Jasmonate ZIM domain (JAZ1), which is ubiquitinated and subsequently subjected to proteasomal degradation releasing the repression of MYC2, thereby activating expression of JA responsive genes. Further, both Novel Interactor of JAZ (NINJA) and Topless (TPL) proteins function as negative regulators of jasmonate responses. Although there has been remarkable progress in recent years, many open questions remain to be answered regarding jasmonate signaling during herbivory.