Abstract:

Being natural plant antimicrobials, saponins have potential for use as biopesticides. Nevertheless, their activity in plant-pathogen interaction is poorly understood. We performed a comparative study of saponins' antifungal activities on important crop pathogens based on their effective dose (EC₅₀) values. Among those saponins tested, aescin showed itself to be the strongest antifungal agent. The antifungal effect of aescin could be reversed by ergosterol, thus suggesting that aescin interferes with fungal sterols. We tested the effect of aescin on plant-pathogen interaction in two different pathosystems: Brassica napus versus (fungus) Leptosphaeria maculans and Arabidopsis thaliana versus (bacterium) Pseudomonas syringae pv tomato DC3000 (Pst DC3000). We analyzed resistance assays, defense gene transcription, phytohormonal production, and reactive oxygen species production. Aescin activated B. napus defense through induction of the salicylic acid pathway and oxidative burst. This defense response led finally to highly efficient plant protection against L. maculans that was comparable to the effect of fungicides. Aescin also inhibited colonization of A. thaliana by Pst DC3000, the effect being based on active elicitation of salicylic acid (SA)-dependent immune mechanisms and without any direct antibacterial effect detected. Therefore, this study brings the first report on the ability of saponins to trigger plant immune responses. Taken together, aescin in addition to its antifungal properties activates plant immunity in two different plant species and provides SA-dependent resistance against both fungal and bacterial pathogens.

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Dual Mode of the Saponin Aescin in Plant Protection: Antifungal Agent and Plant Defense Elicitor

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^{Laboratory of Pathological Plant Physiology, Institute of Experimental Botany of The Czech Academy of Sciences, Prague, Czechia}

^{Laboratory of Plant Biochemistry, Department of Biochemistry and Microbiology, University of Chemistry and Technology Prague, Prague, Czechia}

^{Department Genetics, Faculty of Biology, Biocenter, Ludwig-Maximilian-University of Munich (LMU), Martinsried, Germany}

^{Laboratory of Hormonal Regulations in Plants, Institute of Experimental Botany of The Czech Academy of Sciences, Prague, Czechia}

^{Department of Plant Pathology, Agrotest Fyto, Ltd, Kroměrˇíž, Czechia}

^{Department of Botany, Faculty of Science, Palacký University in Olomouc, Olomouc, Czechia}

Edited by: Ivan Baccelli, Istituto per la Protezione sostenibile delle Piante, Sede Secondaria Firenze, Italy

Reviewed by: Eugenio Llorens, Tel Aviv University, Israel; Hidenori Matsui, Okayama University, Japan

*Correspondence: Lucie Trdá, moc.liamg@adrt.eicul; zc.sac.beu@ladrt

This article was submitted to Plant Microbe Interactions, a section of the journal Frontiers in Plant Science

Edited by: Ivan Baccelli, Istituto per la Protezione sostenibile delle Piante, Sede Secondaria Firenze, Italy

Reviewed by: Eugenio Llorens, Tel Aviv University, Israel; Hidenori Matsui, Okayama University, Japan

Received 2019 Aug 16; Accepted 2019 Oct 17.

This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

Abstract

Being natural plant antimicrobials, saponins have potential for use as biopesticides. Nevertheless, their activity in plant–pathogen interaction is poorly understood. We performed a comparative study of saponins' antifungal activities on important crop pathogens based on their effective dose (EC₅₀) values. Among those saponins tested, aescin showed itself to be the strongest antifungal agent. The antifungal effect of aescin could be reversed by ergosterol, thus suggesting that aescin interferes with fungal sterols. We tested the effect of aescin on plant–pathogen interaction in two different pathosystems: Brassica napus versus (fungus) Leptosphaeria maculans and Arabidopsis thaliana versus (bacterium) Pseudomonas syringae pv tomato DC3000 (Pst DC3000). We analyzed resistance assays, defense gene transcription, phytohormonal production, and reactive oxygen species production. Aescin activated B. napus defense through induction of the salicylic acid pathway and oxidative burst. This defense response led finally to highly efficient plant protection against L. maculans that was comparable to the effect of fungicides. Aescin also inhibited colonization of A. thaliana by Pst DC3000, the effect being based on active elicitation of salicylic acid (SA)-dependent immune mechanisms and without any direct antibacterial effect detected. Therefore, this study brings the first report on the ability of saponins to trigger plant immune responses. Taken together, aescin in addition to its antifungal properties activates plant immunity in two different plant species and provides SA-dependent resistance against both fungal and bacterial pathogens.

Keywords: Brassica napus, Leptosphaeria maculans, salicylic acid, fungicide, Pseudomonas syringae, Arabidopsis thaliana, EC₅₀

Abstract

Acknowledgments

The authors would like to thank T. Rouxel for L. maculans JN2 isolate, Andrea Kung Wai and English Editorial Services for editing, and Iva Trdá for her technical assistance that enabled us to complete the manuscript.

Acknowledgments

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