Histone H 3 K 9 and H 3 K 27 methylation regulates fungal alkaloid biosynthesis in a fungal endophyte–plant symbiosis

Summary E pichloё festucae is a filamentous fungus that forms a mutually beneficial symbiotic association with L olium perenne. This endophyte synthesizes bioprotective lolitrems ( ltm ) and ergot alkaloids ( eas ) in planta but the mechanisms regulating expression of the corresponding subtelomeric gene clusters are not known. We show here that the status of histone H 3 lysine 9 and lysine 27 trimethylation ( H 3 K 9me3/ H 3 K 27me3) at these alkaloid gene loci are critical determinants of transcriptional activity. Using ChIP ‐ qPCR we found that levels of H 3 K 9me3 and H 3 K 27me3 were reduced at these loci in plant infected tissue compared to axenic culture. Deletion of E . festucae genes encoding the H 3 K 9‐ ( ClrD ) or H 3 K 27‐ ( EzhB ) methyltransferases led to derepression of ltm and eas gene expression under non‐symbiotic culture conditions and a further enhancement of expression in the double deletion mutant. These changes in gene expression were matched by corresponding reductions in H 3 K 9me3 and H 3 K 27me3 marks. Both methyltransferases are also important for the symbiotic interaction between E . festucae and L . perenne . Our results show that the state of H 3 K 9 and H 3 K 27 trimethylation of E . festucae chromatin is an important regulatory layer controlling symbiosis‐specific expression of alkaloid bioprotective metabolites and the ability of this symbiont to form a mutualistic interaction with its host.