The role of SreA-mediated iron regulation in maintaining Epichloë festucae-Lolium perenne symbioses

In ascomycetes and basidiomycetes, iron-responsive GATA-type transcriptional repressors are involved in regulating iron homeostasis. Functional characterisation of one such protein, SreA from Epichloë festucae, a fungal endosymbiont of cool-season grasses, indicates that regulation of iron homeostasis processes is critical for symbiotic maintenance. The deletion of sreA (ΔsreA) led to the gradual loss of the endophyte from perennial ryegrass. SreA negatively regulates siderophore biosynthesis and high affinity iron uptake systems by E. festucae as in other fungi. The endophyte tightly controls iron acquisition from the host apoplast via SreA, as ΔsreA mutants induce premature chlorosis. E. festucae appears to have a tightly regulated iron management system for balancing growth and survival that prevents over-competition with the host for iron in the intercellular niche, thus promoting mutualistic associations. Mutations that interfere with Epichloë iron management negatively impact iron-dependent fungal growth and destabilise mutualistic plant - fungal associations.