title: Reactive oxygen species play a role in regulating a fungus-perennial ryegrass mutualistic interaction.
abstract: Although much is known about the signals and mechanisms that lead to pathogenic interactions between plants and fungi, comparatively little is known about fungus-plant mutualistic symbioses. We describe a novel role for reactive oxygen species (ROS) in regulating the mutualistic interaction between a clavicipitaceous fungal endophyte, Epichloë festucae, and its grass host, Lolium perenne. In wild-type associations, E. festucae grows systemically in intercellular spaces of leaves as infrequently branched hyphae parallel to the leaf axis. A screen to identify symbiotic genes isolated a fungal mutant that altered the interaction from mutualistic to antagonistic. This mutant has a single-copy plasmid insertion in the coding region of a NADPH oxidase gene, noxA. Plants infected with the noxA mutant lose apical dominance, become severely stunted, show precocious senescence, and eventually die. The fungal biomass in these associations is increased dramatically, with hyphae showing increased vacuolation. Deletion of a second NADPH oxidase gene, noxB, had no effect on the E. festucae-perennial ryegrass symbiosis. ROS accumulation was detected cytochemically in the endophyte extracellular matrix and at the interface between the extracellular matrix and host cell walls of meristematic tissue in wild-type but not in noxA mutant associations. These results demonstrate that fungal ROS production is critical in maintaining a mutualistic fungus-plant interaction.
authors.affiliation: Centre for Functional Genomics, Institute of Molecular BioSciences, Massey University, Private Bag 11 222, Palmerston North, New Zealand.
authors.forename: Aiko
authors.initials: A
authors.lastname: Tanaka
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Christensen
authors.forename: Daigo
authors.initials: D
authors.lastname: Takemoto
authors.forename: Pyoyun
authors.initials: P
authors.lastname: Park
authors.forename: Barry
authors.initials: B
authors.lastname: Scott
mesh_terms: D000595:Amino Acid Sequence; D001203:Ascomycota / Q000235:genetics / Q000472:pathogenicity / Q000502:physiology*; D017124:Conserved Sequence; D004271:DNA, Fungal / Q000235:genetics; D008129:Lolium / Q000382:microbiology / Q000502:physiology*; D008969:Molecular Sequence Data; D019255:NADPH Oxidases / Q000235:genetics; D010935:Plant Diseases / Q000382:microbiology; D017382:Reactive Oxygen Species / Q000378:metabolism*; D015183:Restriction Mapping; D020133:Reverse Transcriptase Polymerase Chain Reaction; D016415:Sequence Alignment; D017384:Sequence Deletion; D017386:Sequence Homology, Amino Acid; D013559:Symbiosis; D014170:Transformation, Genetic
chemical_list: D004271:DNA, Fungal; D017382:Reactive Oxygen Species; D019255:NADPH Oxidases