A plant-specific family of WRKY
transcription factors regulates plant responses to
pathogens and abiotic stresses. Here, we identify two insect-responsive WRKY genes in the native
tobacco Nicotiana attenuata: WRKY3, whose transcripts accumulate in response to
wounding, and WRKY6, whose
wound responses are significantly amplified when fatty acid-amino acid conjugates (FACs) in
larval oral
secretions are introduced into
wounds during feeding. WRKY3 is required for WRKY6 elicitation, yet neither is elicited by treatment with the
phytohormone wound signal
jasmonic acid. Silencing either WRKY3 or WRKY6, or both, by stable transformation makes plants highly vulnerable to herbivores under glasshouse conditions and in their native
habitat in the Great Basin Desert, Utah, as shown in three field seasons. This susceptibility is associated with
impaired jasmonate (JA) accumulation and impairment of the direct (
trypsin proteinase inhibitors) and indirect (volatiles) defenses that JA signaling mediates. The response to
wounding and herbivore-specific signals (FACs) demonstrates that these WRKYs help plants to differentiate mechanical
wounding from herbivore attack, mediating a plant's herbivore-specific defenses. Differences in responses to single and multiple elicitations indicate an important role of WRKY3 and WRKY6 in potentiating and/or sustaining active JA levels during continuous insect attack.
