Endophyte production of reactive oxygen species is critical for maintaining the mutualistic symbiotic interaction between Epichloe festucae and Pooid grasses

Abstract

Perennial ryegrass, tall fescue and meadow fescue infected with a noxA mutant defective in the ability to produce reactive oxygen species (ROS), had a stunted phenotype and showed premature senescence. Microscopic observations of leaf tissue from perennial ryegrass and tall fescue showed a lack of regulated growth of mutant hyphae in these tissues with increasedv branching, growth and vascular colonisation. However, the fungal phenotype of noxA-infected meadow fescue was very similar to the wild-type phenotype suggesting that an increase in fungal biomass and vascular bundle colonisation is not necessarily a requirement for host stunting. An alternative hypothesis to explain the stunting phenotype is a breakdown in normal signaling between endophyte and host that is ROS dependent. Keywords: Epichloë festucae, Lolium perenne, NoxA, NADPH oxidase, reactive oxygen species (ROS)