cAMP Signaling Regulates Synchronised Growth of SymbioticEpichloëFungi with the Host GrassLolium perenne.
The seed-transmitted fungal symbiont,Epichloë festucae, colonizes grasses by infecting host tissues as they form on the shoot apical meristem (SAM) of the seedling. How this fungus accommodates the complexities of plant development to successfully colonize the leaves and inflorescences is unclear. Since adenosine 3', 5'-cyclic monophosphate (cAMP)-dependent signaling is often essential for host colonization by fungal pathogens, we disrupted the cAMP cascade by insertional mutagenesis of theE. festucaeadenylate cyclase gene (acyA). Consistent with deletions of this gene in other fungi,acyAmutants had a slow radial growth rate in culture, and hyphae were convoluted and hyper-branched suggesting that fungal apical dominance had been disrupted. Nitro blue tetrazolium (NBT) staining of hyphae showed that cAMP disruption mutants were impaired in their ability to synthesize superoxide, indicating that cAMP signaling regulates accumulation of reactive oxygen species (ROS). Despite significant defects in hyphal growth and ROS production,E. festucaeΔacyAmutants were infectious and capable of forming symbiotic associations with grasses. Plants infected withE. festucaeΔacyAwere marginally less robust than the wild-type (WT), however hyphae were hyper-branched, and leaf tissues heavily colonized, indicating that the tight regulation of hyphal growth normally observed in maturing leaves requires functional cAMP signaling.
Forage Science, AgResearch Ltd., Grasslands Research Centre Palmerston North, New Zealand.
Christine R
CR
Voisey
Formally of Forage Improvement, AgResearch Ltd., Grasslands Research Centre Palmerston North, New Zealand.
Michael T
MT
Christensen
Forage Science, AgResearch Ltd., Grasslands Research Centre Palmerston North, New Zealand.
Linda J
LJ
Johnson
Forage Science, AgResearch Ltd., Grasslands Research Centre Palmerston North, New Zealand.
Natasha T
NT
Forester
Forage Science, AgResearch Ltd., Grasslands Research Centre Palmerston North, New Zealand.
Milan
M
Gagic
Forage Science, AgResearch Ltd., Grasslands Research Centre Palmerston North, New Zealand.
Gregory T
GT
Bryan
Forage Science, AgResearch Ltd., Grasslands Research Centre Palmerston North, New Zealand.
Wayne R
WR
Simpson
Biotelliga Ltd., Institute for Innovation in Biotechnology Auckland, New Zealand.
Damien J
DJ
Fleetwood
Forage Science, AgResearch Ltd., Grasslands Research Centre Palmerston North, New Zealand.
Stuart D
SD
Card
Bioinformatics and Statistics Team, AgResearch Ltd., Grasslands Research Centre Palmerston North, New Zealand.
John P
JP
Koolaard
Bioinformatics and Statistics Team, AgResearch Ltd., Lincoln Research Centre Christchurch, New Zealand.
Paul H
PH
Maclean
Forage Science, AgResearch Ltd., Grasslands Research Centre Palmerston North, New Zealand.
Richard D
RD
Johnson
Epichloë festucae; Lolium perenne; cAMP signaling; hyphal branching; reactive oxygen species; symbiosis