Metabolism of the plant hormone jasmonate: a sentinel for tissue damage and master regulator of stress response

Despite being the major dietary source for countless insects, plants have not only survived but thrived on earth and represent arguably the largest terrestrial biomass. This is because plants, instead of falling passive victims to the insects, have come to possess numerous defense strategies including production of insect poisons, deterrents, and other anti-nutritive compounds. A significant part of these built-in defenses are inducible and tactfully coordinated with plant growth in a manner that maximizes return on investment. The lipid-derived signal jasmonate (JA) orchestrates many of these inducible defense responses. JA has a similar evolutionary origin as eicosanoids which play critical roles in mammalian wound and inflammatory responses indicating cross-kingdom adoption of lipid-derived signals for use against tissue injuries. The molecular perception and signaling mechanism of JA indicates that the intracellular concentration of a derivative, jasmonoyl-l-isoleucine (JA-Ile), is the major determinant factor for the dynamic regulation of the JA signaling system. Interdisciplinary methods including recombinant enzyme assays, mass spectrometry based hormone profiling, genetics, genomics, and the model plant Arabidopsis thaliana have assisted in elucidating metabolic pathways controlling JA-Ile homeostasis. Along with the relatively well established biosynthetic enzymes, more recently discovered catabolic pathways as well as areas that need new discoveries are discussed herein. Knowledge obtained from the JA-dependent stress adaptive responses are expected to have agricultural and industrial impact in the future toward the development of environmentally friendly ways of managing pests and tapping into a largely unexplored treasure trove of plant-derived specialized metabolites for human use.