Abstract
Histone acetylation, balanced by histone acetyltransferase (HAT) and histone deacetylase (HDAC) complexes, affects dynamic transitions of chromatin structure to regulate transcriptional accessibility. However, little is known about the interplay between HAT and HDAC complexes in Fusarium graminearum, a causal agent of Fusarium Head Blight (FHB) that uniquely contains chromosomal regions enriched for house-keeping or infection-related genes. In this study, we identified the ortholog of the human inhibitor of growth (ING1) gene in F. graminearum (FNG1) and found that it specifically interacts with the FgEsa1 HAT of the NuA4 complex. Deletion of FNG1 led to severe growth defects and blocked conidiation, sexual reproduction, DON production, and plant infection. The fng1 mutant was normal in H3 acetylation but significantly reduced in H4 acetylation. A total of 34 spontaneous suppressors of fng1 with faster growth rate were isolated. Most of them were still defective in sexual reproduction and plant infection. Thirty two of them had mutations in orthologs of yeast RPD3, SIN3, and SDS3, three key components of the yeast Rpd3L HDAC complex. Four mutations in these three genes were verified to suppress the defects of fng1 mutant in growth and H4 acetylation. The rest two suppressor strains had a frameshift or nonsense mutation in a glutamine-rich hypothetical protein that may be a novel component of the FgRpd3 HDAC complex in filamentous fungi. FgRpd3, like Fng1, localized in euchromatin. Deletion of FgRPD3 resulted in severe growth defects and elevated H4 acetylation. In contract, the Fgsds3 deletion mutant had only a minor reduction in growth rate but FgSIN3 appeared to be an essential gene. RNA-seq analysis revealed that 48.1% and 54.2% of the genes with altered expression levels in the fng1 mutant were recovered to normal expression levels in two suppressor strains with mutations in FgRPD3 and FgSDS3, respectively. Taken together, our data showed that Fng1 is important for H4 acetylation as a component of the NuA4 complex and functionally related to the FgRpd3 HDAC complex for transcriptional regulation of genes important for growth, conidiation, sexual reproduction, and plant infection in F. graminearum.
Highlights
The acetylation of conserved lysine (K) residues in the N-terminal tails of core histone proteins is known to affect dynamic chromatin structure and function [1, 2]
FgRPD3, FgSIN3, and FgSDS3, are key components of the Rpd3 histone deacetylase (HDAC) complex, the other one encodes a glutamine-rich protein appeared to be a novel component of the Rpd3 HDAC complex in filamentous ascomycetes
Most of spontaneous suppressors were still defective in sexual reproduction and plant infection, indicating a stage-specific relationship between Fng1 and the Rpd3 HDAC complex
Summary
The acetylation of conserved lysine (K) residues in the N-terminal tails of core histone proteins is known to affect dynamic chromatin structure and function [1, 2]. Most HAT enzymes exist in multi-protein complexes, allowing the enzymes to carry out specific functions in the cell. In the budding yeast Saccharomyces cerevisiae, histone acetyltransferases Sas and Esa are the catalytic subunits of the NuA3 (Nucleosome Acetyltransferase of histone H3) and NuA4 (Nucleosome Acetyltransferase of histone H4) HAT complexes, respectively [5,6,7]. A general activator of gene transcription, is required for both the HAT activity and integrity of the NuA3 complex consisting of Yng, Eaf, and two other proteins [6]. In comparison with the NuA3 complex, the NuA4 complex is more complex and consists of Esa HAT and 12 other proteins. In S. cerevisiae, ESA1 is the only essential HAT gene and the esa1ts mutant is blocked in the cell cycle at restrictive temperatures [10].
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