The conserved U1 snRNP subunit FgLuc7 regulates sexual development and pre-mRNA processing in fusarium graminearum

The U1 small nuclear ribonucleoprotein (U1 snRNP) is an essential spliceosome component that mediates pre-mRNA splicing. Although the molecular function of Luc7 proteins is broadly conserved in eukaryotes, whether this core splicing factor acquires developmentally specialized functions in filamentous fungi remains unclear. Here, we investigated the U1 snRNP-associated protein FgLuc7 in Fusarium graminearum. Remarkably, deletion of FgLuc7 had little detectable effect on vegetative growth under standard conditions but caused a complete failure of ascus and ascospore development despite normal perithecium formation, revealing a pronounced requirement for FgLuc7 during sexual development. The ∆FgLuc7 mutant also exhibited increased sensitivity to cell wall- and membrane-associated stressors. Yeast two-hybrid (Y2H) and co-immunoprecipitation (Co-IP) assays revealed that FgLuc7 physically interacts with multiple U1 snRNP components, including FgU1-70 K, FgSmB/B, and FgSnu71, supporting conservation of its association with the U1 splicing machinery. RNA-seq analysis revealed that FgLuc7 deletion affects 2505 genes at the expression level and causes differential alternative splicing in 202 genes in the ΔFgLuc7 mutant, with intron retention (IR) accounting for 67% of all AS events. Notably, three genes essential for sexual reproduction (FgCak1, FgGil1, FgAreA) showed significantly reduced splicing efficiency in the absence of FgLuc7. Overall, our results demonstrate that a conserved U1 snRNP-associated factor FgLuc7 is a key regulator of pre-mRNA splicing and sexual reproduction in F. graminearum, providing a mechanistic basis for further dissecting stage-specific splicing networks controlling ascus and ascospore formation.