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Abstract
Beneficial Pseudomonas spp. produce an array of antimicrobial secondary metabolites such as cyclic lipopeptides (CLPs). We investigated the capacity of CLP-producing Pseudomonas strains and their crude CLP extracts to control rice blast caused by Magnaporthe oryzae, both in a direct manner and via induced systemic resistance (ISR). In planta biocontrol assays showed that lokisin-, white line inducing principle (WLIP)-, entolysin- and N3-producing strains successfully induced resistance to M. oryzae VT5M1. Furthermore, crude extracts of lokisin, WLIP and entolysin gave similar ISR results when tested in planta. In contrast, a xantholysin-producing strain and crude extracts of N3, xantholysin and orfamide did not induce resistance against the rice blast disease. The role of WLIP in triggering ISR was further confirmed by using WLIP-deficient mutants. The severity of rice blast disease was significantly reduced when M. oryzae spores were pre-treated with crude extracts of N3, lokisin, WLIP, entolysin or orfamide prior to inoculation. In vitro microscopic assays further revealed the capacity of crude N3, lokisin, WLIP, entolysin, xantholysin and orfamide to significantly inhibit appressoria formation by M. oryzae. In addition, the lokisin and WLIP biosynthetic gene clusters in the producing strains are described. In short, our study demonstrates the biological activity of structurally diverse CLPs in the control of the rice blast disease caused by M. oryzae. Furthermore, we provide insight into the non-ribosomal peptide synthetase genes encoding the WLIP and lokisin biosynthetic machineries.
Highlights
Fluorescent Pseudomonas spp. belonging to the phylum Proteobacteria are prominent among rhizosphere and soil microbes (Philippot et al, 2013)
We showed that purified lokisin, entolysin, xantholysin, and white line inducing principle (WLIP) could interact with the mycelium of P. myriotylum resulting in hyphal leakage and/or branching (Oni et al, 2019a)
Results showed that N3, WLIP, lokisin- and entolysin-producing strains, COW3, COW10, COR10 and COR5, respectively, successfully induced resistance to M. oryzae in rice
Summary
Fluorescent Pseudomonas spp. belonging to the phylum Proteobacteria are prominent among rhizosphere and soil microbes (Philippot et al, 2013). Pseudomonas species are metabolically versatile and produce an array of secondary metabolites including various antibiotics and cyclic lipopeptides (CLPs) (Gross and Loper, 2009). Pseudomonas CLPs are currently classified into at least 14 different groups based on the length of the oligopeptide (Gross and Loper, 2009; Olorunleke et al, 2015b; Geudens and Martins, 2018). Under in vitro and in vivo conditions, Pseudomonas CLPs have been shown to possess biocontrol potential against several plant pathogens including Pythium myriotylum (Oni et al, 2019a,b), Pythium aphanidermatum (Michelsen et al, 2015), Phytophthora infestans, Phytophthora capsici and Pythium ultimum (Van Der Voort et al, 2015), Rhizoctonia solani (D’aes et al, 2014; Michelsen et al, 2015; Olorunleke et al, 2015a), Cochliobolus miyabeanus, and Magnaporthe oryzae (Ma et al, 2017)
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