Reprogramming of the apoplast metabolome of Lolium perenne upon infection with the mutualistic symbiont Epichloë festucae

is an endophytic fungus that forms a mutualistic symbiotic association with . Here we analysed how the metabolome of the ryegrass apoplast changed upon infection of this host with sexual and asexual isolates of . A metabolite fingerprinting approach was used to analyse the metabolite composition of apoplastic wash fluid from non-infected and infected . 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 mass spectrometry was used to identify a novel product of a secondary metabolite gene cluster. Metabolites likely to be present in the apoplast were identified using the MarVis Pathway in combination with the BioCyc and KEGG databases, and an in-house 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 -derived metabolites, we deleted a gene encoding a NRPS () that is highly expressed . Comparative mass spectrometric analysis of apoplastic wash fluid from wild-type- versus mutant- infected plants identified a novel Leu/Ile glycoside metabolite present in the former.