Plant elicitor peptides in induced defense against insects

•Plant Elicitor Peptides (Peps) are amplifiers of plant pathogen defense responses.•A maize Pep is a potent inducer of direct and indirect anti-herbivore defense.•Peps are conserved mediators of anti-herbivore responses in diverse plant species.•Peps are unrelated to systemin but many are functionally orthologous.

Over 20 years ago the peptide systemin was discovered to be an integral regulator of anti-herbivore defense responses in Solanaceous plants. However, other peptides of similar function have remained elusive. Plant Elicitor Peptides (Peps) were initially discovered in Arabidopsis as mediators of basal immune responses protective against invading pathogens. Recently a Pep from maize, ZmPep3, was demonstrated to be a potent regulator of anti-herbivore defenses. ZmPep3 was as active as the Lepidopteran elicitor N-linolenoyl-l-glutamine (Gln-18:3) in stimulating volatile emission and accumulation of defense transcripts and metabolites, resulting in both attraction of the parasitoid Cotesia marginiventris and suppressed growth of Spodoptera exigua larvae. Orthologues of Peps in Solanaceous and Fabaceous plants also trigger emission of herbivore-associated volatiles, indicating that Peps have a conserved role as regulators of plant defense against herbivores in diverse species. This conservation of a peptide signal and cognate receptor for activation of plant defense responses reveals a widespread regulatory motif and provides opportunities for manipulation of plant resistance.

Graphical abstractOverview of ZmPep3 regulation of anti-herbivore defense. During herbivory by Spodoptera larvae, perception of HAMPs such as N-linolenoyl-l-glutamine (Gln:18:3) triggers transcriptional (and possibly proteolytic) activation of ZmPep3. ZmPep3 acts as an amplifier of signaling initiated by Gln-18:3, with both molecules stimulating a burst of jasmonic acid (JA) and ethylene (ET). In turn, this promotes transcriptional and metabolic reprogramming resulting in both emission of volatiles attractive to Cotesia marginiventris parasitoids and accumulation of proteins and benzoxazinoids that directly suppress larval growth.Download full-size image