Herbivore-associated Molecular Patterns Research Articles

Cytokinin levels and signaling respond to wounding and the perception of herbivore elicitors in Nicotiana attenuata.

Nearly half a century ago insect herbivores were found to induce the formation of green islands by manipulating cytokinin (CK) levels. However, the response of the CK pathway to attack by chewing insect herbivores remains unclear. Here, we characterize the CK pathway of Nicotiana attenuata (Torr. ex S. Wats.) and its response to wounding and perception of herbivore-associated molecular patterns (HAMPs). We identified 44 genes involved in CK biosynthesis, inactivation, degradation, and signaling. Leaf wounding rapidly induced transcriptional changes in multiple genes throughout the pathway, as well as in the levels of CKs, including isopentenyladenosine and cis-zeatin riboside; perception of HAMPs present in the oral secretions (OS) of the specialist herbivore Manduca sexta amplified these responses. The jasmonate pathway, which triggers many herbivore-induced processes, was not required for these HAMP-triggered changes, but rather suppressed the CK responses. Interestingly CK pathway changes were observed also in systemic leaves in response to wounding and OS application indicating a role of CKs in mediating long distance systemic processes in response to herbivory. Since wounding and grasshopper OS elicited similar accumulations of CKs in Arabidopsis thaliana L., we propose that CKs are integral components of wounding and HAMP-triggered responses in many plant species.

Insect herbivores selectively mute GLV production in plants

Through co-evolution insect herbivores have developed a myriad of strategies to manipulate host plant defense responses that include the synthesis of defensive compounds whose composition depends on the insect feeding mode. Among the plant-produced compounds are jasmonates (JAs), and Green Leafy Volatiles (GLVs), metabolites produced by the two parallel and competing branches of the oxylipin pathway. Here we provide evidence that chewing insects stimulate JA production but suppress the synthesis of GLVs through the transcriptional and post transcriptional reprogramming of critical genes in the corresponding pathway. We further establish that herbivore-derived elicitors known as Herbivore-Associated Molecular Patterns (HAMPs) are responsible for the reprogramming of these pathway genes. Through this strategy chewing herbivores coerce the plant signaling machinery that would otherwise leads to a reduction in the nutritional quality of the immediate and neighboring plants, and additionally shelters the herbivores from their natural enemies that are otherwise guided by the GLV cues to prey-infested plants.