The pre-mRNA processing factor Prp6 is an essential component of the U4/U6.U5 tri-small nuclear ribonucleoprotein (snRNP).  In a previous study, mutations were identified in the PRP6 ortholog in four suppressors of Fgprp4 that was deleted of the only kinase FgPrp4 among the spliceosome components in the plant pathogenic fungus Fusarium graminearum.  In this study, we identified additional suppressor mutations in FgPrp6 and determined the suppressive effects of selected mutations.  In total, 12 mutations of FgPRP6 were identified in 20 suppressors of Fgprp4 by sequencing analysis.  Whereas three mutation sites are in the linker region of FgPrp6, seven are in the first two HAT repeats.  RNA-seq analysis showed that suppressor mutations on different sites caused different splicing efficiency recovery.  The suppressive effects of E308K and R230H were verified.  Similar to human and fission yeast, the FgPrp6 was phosphorylated by the FgPrp4 kinase.  Interestingly, the conserved Prp4-phosphorylation sites T261, T219&T221, and predicted phosphorylation sites T199&T200 on FgPrp6 were dispensable for the function of FgPrp6 in hyphal growth and sexual reproduction but important in plant infection.  They are required for the infectious growth of F. graminearum in wheat lemma.  RNA-seq analysis of the wheat lemma infected with Fgprp6/FgPRP6^Δ199–221-GFP or Fgprp6/FgPRP6^Δ250–262-GFP showed that 28 and 35% introns had splicing defects, respectively, which may be responsible for their defects in plant infection.    

The Rpd3 histone deacetylase complex is a multiple-subunit complex that mediates the regulation of chromatin accessibility and gene expression. Sin3, the largest subunit of Rpd3 complex, is conserved in a broad range of eukaryotes. Despite being a molecular scaffold for complex assembly, the functional sites and mechanism of action of Sin3 remain unexplored. In this study, we functionally characterized a glutamate residue (E810) in FgSin3, the ortholog of yeast Sin3 in Fusarium graminearum (known as wheat scab fungus). Our findings indicate that E810 was important for the functions of FgSin3 in regulating vegetative growth, sexual reproduction, wheat infection, and DON biosynthesis. Furthermore, the E810K missense mutation restored the reduced H4 acetylation caused by the deletion of FNG1, the ortholog of the human inhibitor of growth (ING1) gene in F. graminearum. Correspondingly, the defects of the fng1 mutant were also partially rescued by the E810K mutation in FgSin3. Sequence alignment and evolutionary analysis revealed that E810 residue is well-conserved in fungi, animals, and plants. Based on Alphafold2 structure modeling, E810 localized on the FgRpd3-FgSin3 interface for the formation of a hydrogen bond with FgRpd3. Mutation of E810 disrupts the hydrogen bond and likely affects the FgRpd3-FgSin3 interaction. Taken together, E810 of FgSin3 is functionally associated with Fng1 in the regulation of H4 acetylation and related biological processes, probably by affecting the assembly of the Rpd3 complex.