Biosynthesis of an extracellular siderophore is essential for maintenance of mutualistic endophyte-grass symbioses

Abstract

We have identified a novel siderophore from the mutualistic grass symbiont Epichloë festucae. Targeted gene replacement of a non-ribosomal peptide synthetase (termed sidF) from E. festucae eliminated biosynthesis of this extracellular siderophore. Structural characterisation, based on extensive mass spectrometry showed similarities to fusarinine-type siderophores. Plants inoculated with strains carrying a targeted deletion in sidF have a dramatic phenotype. Siderophore loss changed a mutualistic symbiont into an antagonistic fungus, causing de-regulation and proliferation of fungal hyphae, plant stunting and sometimes even tiller death. We hypothesise that loss of the biosynthesis of the siderophore disrupts iron homeostasis within the whole symbiotum, which is a critical factor for maintenance of mutualistic endophyte-grass symbioses. Keywords: siderophore, iron homeostasis, NRPS