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.

A Bifunctional Synthetic Peptide With Antimicrobial and Plant Elicitation Properties That Protect Tomato Plants From Bacterial and Fungal Infections

“…For the ethylene treatment, plants were enclosed in a sealed chamber and exposed to ethylene obtained by reacting ethephon (1 mM) (Nufarm España, Spain) with a disodium hydrogen phosphate buffer (2.5 mM) (Zhang and Wen, 2010 ). The concentrations of the peptides BP100 and BP178 were chosen on the basis of the concentrations that were found effective against infections by plant pathogens observed in planta assays that were previously reported (Badosa et al, 2017 ; Caravaca-Fuentes et al, 2021 ). In the case of SA, JA, and ethylene, the concentrations were selected because they were used in other reports on topical application of defense elicitors in plants (Reignault and Walters, 2007 ; Rivas-San and Plasencia, 2011 ; Zhang et al, 2011 ).…”

“…Peptides BP178 (KKLFKKILKYLAGPAGIGKFLHSAKKDEL-OH), flg15 (RINSAKDDAAGLQIA-OH), and BP100 (KKLFKKILKYL-NH 2 ) were synthesized using the solid phase procedure as previously described (Badosa et al, 2007(Badosa et al, , 2013Caravaca-Fuentes et al, 2021) (Supplementary Figure 1). An Fmoc-Rink-MBHA resin (0.55 mmol/g) was used for the synthesis of BP100, and a PAC-ChemMatrix resin (0.66 mmol/g) for the synthesis of flg15 and BP178.…”

“…Interestingly, analogs of flagellin (flg22 or flg15) and several natural or synthetic peptides were reported to trigger innate immunity in plants (Meindl et al, 2000 ; Brotman et al, 2009 ; Wei et al, 2017 ; Czékus et al, 2021 ). In this context, flg15 induced ROS production and the expression of several genes involved in salicylic acid, jasmonic acid, and ethylene-signaling pathways in tomato plants (Robatzek et al, 2007 ; Caravaca-Fuentes et al, 2021 ).…”

“…In particular, we designed and synthesized a library of linear undecapeptides (CECMEL11) (Ferré et al, 2006 ; Badosa et al, 2007 ), from which we identified sequences with an excellent biological activity profile that have been used successfully to control diseases caused by fungal and bacterial plant pathogens of economic importance (Badosa et al, 2007 , 2009 ; Baró et al, 2020 ). Several peptide conjugates from members of the CECMEL11 library, like BP358 (containing flg15 and BP16), showed antimicrobial and plant defense elicitation activities in the Erwinia amylovora /pear pathosystem (Caravaca-Fuentes et al, 2021 ).…”

Table_1.DOCX

“…The PAC-MBHA resin was employed to prepare C-terminal carboxylic acid peptides whereas the Fmoc-Rink-ChemMatrix and the Fmoc-Rink-MBHA resins served for C-terminal peptide amides. Peptide elongation was carried out through sequential steps of Fmoc removal and coupling of the corresponding amino acid as previously described (Caravaca-Fuentes et al, 2021;Oliveras et al, 2021). Once the peptide sequence was completed, each resulting peptidyl resin was treated with trifluoroacetic acid (TFA)/H 2 O/triisopropylsilane (TIS) (95:2.5:2.5).…”