Submitted to: Molecular Plant-Microbe Interactions
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/30/2008
Publication Date: 12/1/2008
Citation: Lysoe, E., Pasquali, M., Klemsdahl, S., Kistler, H.C. 2008. The transcription factor FgStuAp influences spore development, pathogenicity, and secondary metabolism in Fusarium graminearum. Molecular Plant-Microbe Interactions. 90:S3.26-S3.27.
Interpretive Summary: Fusarium graminearum is an important plant-pathogenic fungus and the major cause of cereal head blight. Here, we report the functional analysis of FgStuA, the gene for a transcription factor with homology to key developmental regulators in fungi. The deletion mutant was greatly reduced in pathogenicity on wheat heads and in production of secondary metabolites. Spore production was significantly impaired in FgStuA, which did not develop perithecia and sexual ascospores, and lacked conidiophores and phialides, leading to delayed production of aberrant macroconidia. FgStuAp appears to act as a global regulator that may affect many diverse aspects of the life cycle of F. graminearum. Transcriptome analysis shows that thousands of genes are differentially expressed in the mutant during asexual sporulation and infection of wheat heads and under conditions that induce secondary metabolites, including many that could account for the mutant phenotypes observed. The primary regulatory targets of FgStuAp are likely genes involved in cell-cycle control, and the predicted FgStuAp sequence has an APSES domain, with homology to helixloop-helix proteins involved in cell-cycle regulation. The Aspergillus StuAp response element (A/TCGCGT/ANA/C) was found highly enriched in the promoter sequences of cellcycle genes, which was upregulated in the FgStuA deletion mutant.
Technical Abstract: Members of the APSES family of fungal proteins regulate morphogenesis and virulence in ascomycetes. We deleted the FgStuA gene in Fusarium graminearum and demonstrate its involvement in several different processes. FgStuA is closely related to FoStuA in F. oxysporum and StuA in Aspergillus. Unlike FoStuA mutants in F. oxysporum, the FgStuA mutants were greatly reduced in pathogenicity both on wheat and apple slices. Reduced pathogenicity may be due to decreased levels of trichothecene production (<1% the levels of wildtype). Mutants were also diminished in growth and the aerial mycelium becomes more "wettable" than the wildtype. Several putative hydrophobin genes were shown to be highly down-regulated in the mutant, which may explain the loss of hydrophobicity. FgStuA mutants also were greatly reduced in asexual sporulation and produced no perithecia. Microarray analysis during conditions when the wildtype produced asexual spores and the mutant produced no spores, showed that genes encoding several groups of cell-wall related proteins such as chitinases, glycanases and GPIs, mostly were down-regulated in the mutant. The FgStuA mutant has a white phenotype compared to the red wild-type, and 17 continuous genes, including the known aurofusarin genes, were virtually completely turned off in the mutant. Also eight continuous genes, including genes encoding a putative PKS-NPS hybrid, where found to be down-regulated in the mutant during "spore-production". In general it seems like the StuA protein in F. graminearum functions as an activator of genes, as in F. oxysporum and budding yeast, and not as a repressor as it has been suggested for A. nidulans.