Abstract
Summary Epichloë festucae is an endophytic fungus that forms a symbiotic association with Lolium perenne. Here we analysed how the metabolome of the ryegrass apoplast changed upon infection of this host with sexual and asexual isolates of E. festucae.A metabolite fingerprinting approach was used to analyse the metabolite composition of apoplastic wash fluid from uninfected and infected L. perenne. Metabolites enriched or depleted in one or both of these treatments were identified using a set of interactive tools. A genetic approach in combination with tandem MS was used to identify a novel product of a secondary metabolite gene cluster.Metabolites likely to be present in the apoplast were identified using marvis in combination with the BioCyc and KEGG databases, and an in‐house Epichloë metabolite database. We were able to identify the known endophyte‐specific metabolites, peramine and epichloëcyclins, as well as a large number of unknown markers.To determine whether these methods can be applied to the identification of novel Epichloë‐derived metabolites, we deleted a gene encoding a NRPS (lgsA) that is highly expressed in planta. Comparative MS analysis of apoplastic wash fluid from wild‐type‐ vs mutant‐infected plants identified a novel Leu/Ile glycoside metabolite present in the former.
Highlights
The fungal endophyte Epichlo€e festucae forms symbiotic associations with temperate grasses of the Festuca, Lolium and Koeleria genera (Leuchtmann et al, 1994)
Endophyte symbiosis alters the metabolite composition of the host apoplast In nature, the secondary metabolites (SMs) composition of E. festucae-infected host tissues varies considerably depending on the E. festucae strain used (Schardl et al, 2007, 2013; Young et al, 2009)
Principal component analysis of this dataset showed a clear separation on principal component 1 (PC1) for the apoplast metabolome of mock-treated and FI1-infected ryegrass, while PC2 separates all three treatments (Fig. S1)
Summary
The fungal endophyte Epichlo€e festucae forms symbiotic associations with temperate grasses of the Festuca, Lolium and Koeleria genera (Leuchtmann et al, 1994). Epichlo€e species growing in planta produce a wide variety of secondary metabolites (SMs) that protect the host against herbivores (Malinowski & Belesky, 2000; Clay & Schardl, 2002; Saikkonen et al, 2016). The most well characterized Epichlo€e SMs are the ergot alkaloids, lolines, indole-diterpenes, and pyrrolopyrazines such as peramine (Young et al, 2005; Schardl et al, 2013; Berry et al, 2015). Ergot alkaloids and indole-diterpenes are anti-mammalian mycotoxins (Florea et al, 2016; Philippe, 2016), while lolines and peramine protect against insect herbivores (Rowan & Gaynor, 1986; Wilkinson et al, 2000; Tanaka et al, 2005; Schardl et al, 2007; Pan et al, 2014)
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