Get ready for infection: Transcriptional profiling reveals virulence-specific traits inside of infection cushions of Fusarium graminearum

Abstract

International audienceThe fungal pathogen Fusarium graminearum forms specialized infection cushions (ICs) essential for penetration of wheat floral-leaf cells. To understand the molecular basis of IC development, ICs and non-invasive runner hyphae (RH) were isolated by laser capture microdissection and subjected to RNAseq. Quantitative expression analysis show marked differences in gene expression patterns between RH and ICs:1. The majority of known and putative secondary metabolite gene clusters, including those responsible for trichothecene and butenolide production, are significantly up-regulated in ICs, 2. Carbohydrate-modifying enzymes (CAZymes) with proven capacities for cell-wall degradation are exclusively present in ICs. In total, 174 genes encoding for CAZymes are differentially expressed (42 in RH, 132 in ICs), 3. Genes encoding for enzymes involved in reactive-oxygen species metabolism reside in the upper ranks of differentially expressed genes (DEGs). Secreted ROS-related enzymes (SREs), presumably involved in plant-defense response, are relatively enriched in ICs, 4. We identified a large subset of transcripts encoding for putative effector proteins. By use of this novel transcriptional profiling of runner hyphae and infection cushions from a fungal plant pathogen obtained under in planta conditions, we gain new insights in the initial infection process of F. graminearum on wheat. Complementary to this approach, functional characterization of genes and histological analyses are ongoing. First results will be presented. We conclude that infection cushions serve as an armory of virulence factors