Two pear phytocytokines PbePep4 and PdrPep6 interfamilially elicit broad-spectrum immunity against various pathogens in crops

Abstract Plant elicitor peptides (Peps) are a class of endogenous phytocytokine that enhances plant innate immunity against diverse pathogens. They are widely distributed in the plant kingdom, yet their interfamily compatibility of Peps perception remains controversial. In this study, two pear (Pyrus L.) Peps, PbePep4 (Pyrus betulifolia) and PdrPep6 (Pyrus ussuriensis x communis Zhongai), were identified and their function in eliciting interfamily immunity was dissected. We found that PbePep4 and PdrPep6 improved resistance of pear leaves to fire blight caused by Erwinia amylovora. Exogenous treatment with PbePep4 and PdrPep6 activated various immune responses in pear leaves, including burst of reactive oxygen species, deposition of callose, phosphorylation of Mitogen-Activated Protein Kinase, and up-regulation of defense genes. Intriguingly, these two pear peptides were able to interfamilially trigger immune responses of plants from Brassicaceae and Cucurbiaceae families. Application with PbePep4 and PdrPep6 enhanced the resistance of Brassicaceae species Arabidopsis thaliana and Brassica napus to Sclerotinia sclerotiorum, and that of Cucurbiaceae species Citrullus lanatus to Botrytis cinerea. We demonstrated that the key of these peptides to induce immunity in cross-family species is associated with the conservation of the conformed motif at the C-terminal of Pep peptides and their six active binding sites in PEPRs in cross-family species from the Rosaceae, Brassicaceae, and Cucurbiaceae. Taken together, our findings not only solved the debate whether plant Peps can only stimulate immunity within the family, but also clarified the exploitation potential of pear Peps as broad-spectrum immune inducers to control disease in crops of at least three families.