The SAGA complex in the rice pathogen Fusarium fujikuroi: structure and functional characterization

Post-translational modification of histones is a crucial mode of transcriptional regulation in eukaryotes. A well-described acetylation modifier of certain lysine residues is the Spt-Ada-Gcn5 acetyltransferase (SAGA) complex assembled around the histone acetyltransferase Gcn5 in Saccharomyces cerevisiae. We identified and characterized the SAGA complex in the rice pathogen Fusarium fujikuroi, well-known for producing a large variety of secondary metabolites (SMs). By using a co-immunoprecipitation approach, almost all of the S. cerevisiae SAGA complex components have been identified, except for the ubiquitinating DUBm module and the chromodomain containing Chd1. Deletion of GCN5 led to impaired growth, loss of conidiation and alteration of SM biosynthesis. Furthermore, we show that Gcn5 is essential for the acetylation of several histone 3 lysines in F. fujikuroi, that is, H3K4, H3K9, H3K18 and H3K27. A genomewide microarray analysis revealed differential expression of about 30% of the genome with an enrichment of genes involved in primary and secondary metabolism, transport and histone modification. HPLCbased analysis of known SMs revealed significant alterations in the Delta gcn5 mutant. While most SM genes were activated by Gcn5 activity, the biosynthesis of the pigment bikaverin was strongly increased upon GCN5 deletion underlining the diverse roles of the SAGA complex in F. fujikuroi.