Jasmonate

Jasmonates are a group of plant signaling molecules derived from the fatty acid linolenic acid. In plants, they function as hormones that regulate defense responses, growth, development, and reproduction. The most well-known jasmonate is jasmonic acid (JA) and its bioactive conjugate JA-Ile, with methyl jasmonate (MeJA) acting as a volatile signaling form.

Biosynthesis of jasmonates occurs mainly through the octadecanoid pathway in chloroplasts and peroxisomes. Linolenic acid is converted by lipoxygenase (LOX) to hydroperoxides, which are processed by allene oxide synthase (AOS) and allene oxide cyclase (AOC) to produce 12-oxo-phytodienoic acid (OPDA). OPDA is transported to peroxisomes and reduced by 12-oxophytodienoate reductase (OPR3) to OPC-8:0, which undergoes β-oxidation to form jasmonic acid. JA can be conjugated with isoleucine by JAR1 to form JA-Ile, the main active hormone. MeJA is formed by methylation of JA and can function as a volatile signal.

Signaling begins with JA-Ile binding to the COI1-JAZ co-receptor complex, an SCF-type E3 ubiquitin ligase. This interaction targets JAZ repressor proteins for ubiquitination and degradation, releasing transcription factors such as MYC2 and related factors to activate JA-responsive genes. The jasmonate response often interacts with other hormonal pathways, notably antagonistically with salicylic acid signaling.

Roles of jasmonates are broad, including defense against herbivores and necrotrophic pathogens, induction of anti-herbivory metabolites and volatiles, wound responses, and regulation of reproductive development, seed germination, and trichome formation. MeJA also mediates interplant communication through airborne signals, linking neighboring plants to JA-regulated defenses.