A Bifunctional Peptide Conjugate That Controls Infections of Erwinia amylovora in Pear Plants

Abstract

In this paper, peptide conjugates were designed and synthesized by incorporating the antimicrobial undecapeptide BP16 at the C- or N-terminus of the plant defense elicitor peptide flg15, leading to BP358 and BP359, respectively. The evaluation of their in vitro activity against six plant pathogenic bacteria revealed that BP358 displayed MIC values between 1.6 and 12.5 μM, being more active than flg15, BP16, BP359, and an equimolar mixture of BP16 and flg15. Moreover, BP358 was neither hemolytic nor toxic to tobacco leaves. BP358 triggered the overexpression of 6 out of the 11 plant defense-related genes tested. Interestingly, BP358 inhibited Erwinia amylovora infections in pear plants, showing slightly higher efficacy than the mixture of BP16 and flg15, and both treatments were as effective as the antibiotic kasugamycin. Thus, the bifunctional peptide conjugate BP358 is a promising agent to control fire blight and possibly other plant bacterial diseases.

Keywords: antimicrobial peptides; fire blight; peptide conjugate; plant-defense elicitors.

Figure 1

Kinetics of survival of E. amylovora in the presence of peptides. Bacterial suspensions were untreated (NTC) or treated with BP16 (50 µM), flg15 (100 µM), BP358 (6.2 µM), or a mixture of flg15 and BP16 at equal molar quantities (25 μM) (Mixture). Viable cells were determined at different time intervals.

Figure 2

Effect of the peptides on the incidence of E. amylovora infections in pear plants. Black bars correspond to assay one and grey bars to assay two. A non-treated control (NTC) and a reference treatment with kasugamycin (KSM) were included. The treatment with a mixture of BP16 and flg15 is labeled as BP16 + flg15. The confidence intervals for the means are indicated on top of the bars. Different letters (capital letters for assay one and lowercase letters for assay two) show significant differences between the treatments according to Duncan’s test (p < 0.05, ANOVA, LSD).