From the Cover: Arabidopsis synchronizes jasmonate-mediated defense with insect circadian behavior

In the battle between plant host and herbivore, plants appear to be disadvantaged due to their relative immobility because once herbivorous insects attack, plants cannot escape by relocating. However, it is well-documented that plants can detect attack by insect herbivores and, in response, activate defense responses (1). These defense responses include accumulation of proteins and compounds that are toxic to and/or act to deter feeding of herbivores, thereby reducing herbivore performance and increasing plant resistance. Jasmonate hormones are critical for plant herbivore defense (1–3) and for the regulation of both herbivore and wound-responsive gene expression (4). Remarkably, many genes regulated in expression by wounding also have strong circadian regulation. Over 40% of genes whose expression is induced by wounding have peak circadian expression at subjective dusk, and over 80% of genes down-regulated by wounding have peak expression at subjective dawn (5). However, it remained to be determined whether this circadian regulation of wound-inducible genes enables plants to anticipate herbivore attack through a cyclical activation of defense response. Here we demonstrate that Arabidopsis plants that are entrained such that their subjective day is in-phase with Trichoplusia ni subjective day have increased resistance to herbivory. In contrast, when the plant subjective day is the insect subjective night, plant resistance is largely lost and T. ni performance is greatly increased. T. ni is shown to display circadian-controlled feeding behavior, peaking during late day. Circadian clock and active jasmonate functions are required for this phase-dependent enhanced resistance. Finally, we show that both jasmonate and salicylate hormone levels are circadian-regulated and thus reveal an underlying mechanism for clock-mediated plant defense.