Mutations in FgPrp6 suppressive to the Fgprp4 mutant in Fusarium graminearum

Abstract

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/FgPRP6Δ199–221-GFP or Fgprp6/FgPRP6Δ250–262-GFP showed that 28 and 35% introns had splicing defects, respectively, which may be responsible for their defects in plant infection.