title: NoxA activation by the small GTPase RacA is required to maintain a mutualistic symbiotic association between Epichloë festucae and perennial ryegrass.
abstract: Small GTPases of the Rac group play a key regulatory role in NADPH oxidase catalysed production of reactive oxygen species (ROS) in mammals and plants, but very little evidence is available for a corresponding role in fungi. We recently showed that ROS produced by a specific fungal NADPH oxidase isoform, NoxA, are crucial in regulating hyphal morphogenesis and growth in the mutualistic symbiotic interaction between Epichloë festucae and perennial ryegrass. We demonstrate here that E. festucae RacA is required for NoxA activation and regulated production of ROS to maintain a symbiotic interaction. Deletion of racA resulted in decreased ROS production, reduction of radial growth and hyper-branching of the hyphae in culture. In contrast, in planta the racA mutant showed extensive colonization of the host plant, resulting in stunting and precocious senescence of the host plants. Strains expressing a dominant active (DA) allele of RacA had increased ROS production, increased aerial hyphae and reduced radial growth. These results demonstrate that RacA plays a crucial role in regulating ROS production by NoxA, in order to control hyphal morphogenesis and growth of the endophyte in planta.
authors.affiliation: Centre for Functional Genomics, Institute of Molecular BioSciences, Massey University, Private Bag 11 222, Palmerston North 4442, New Zealand.
authors.forename: Aiko
authors.initials: A
authors.lastname: Tanaka
authors.forename: Daigo
authors.initials: D
authors.lastname: Takemoto
authors.forename: Gang-Su
authors.initials: GS
authors.lastname: Hyon
authors.forename: Pyoyun
authors.initials: P
authors.lastname: Park
authors.forename: Barry
authors.initials: B
authors.lastname: Scott
mesh_terms: D001203:Ascomycota / Q000235:genetics / Q000472:pathogenicity / Q000502:physiology*; D005656:Fungal Proteins; D015966:Gene Expression Regulation, Fungal; D025301:Hyphae / Q000254:growth & development; D008129:Lolium / Q000382:microbiology / Q000502:physiology*; D008969:Molecular Sequence Data; D020559:Monomeric GTP-Binding Proteins / Q000378:metabolism*; D019255:NADPH Oxidases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D010935:Plant Diseases / Q000382:microbiology; D017382:Reactive Oxygen Species / Q000378:metabolism*; D013559:Symbiosis; D020744:rac GTP-Binding Proteins / Q000378:metabolism
chemical_list: D005656:Fungal Proteins; D017382:Reactive Oxygen Species; D019255:NADPH Oxidases; D020559:Monomeric GTP-Binding Proteins; D020744:rac GTP-Binding Proteins