Mediation of Induced Plant Defenses by the Symbionts of Insect Herbivores

The role of herbivore-associated microbes in modifying plant defenses has received very little attention.  We recently reported that certain insect herbivores such as the Colorado potato beetle secrete symbiotic bacteria during feeding that manipulate plant defenses. The bacteria elicit salicylic acid (SA)-regulated defenses, and because SA signaling often negatively effects jasmonate signaling, plants are unable to fully activate their jasmonate-mediated resistance against the herbivore. From the plants’ perspective, they recognize herbivores not as such, but as microbial threats.

We have found in other herbivorous insects such as caterpillars, that gut symbiotic bacteria may indirectly suppress the production of elicitors in their saliva.  In this case, the bacteria are not secreted during feeding, but instead have an indirect effect on the suppression of induced defenses.  Our results with these insect herbivores add a new dimension of how gut microbes may facilitate the hijacking of plant defense signaling pathways.