FgRIC8 is involved in regulating vegetative growth, conidiation, deoxynivalenol production and virulence in Fusarium graminearum

• FgRIC8 is required for growth, conidiation and DON production.
• FgRIC8 is important for virulence.
• FgRic8 may act as a regulator of G-alpha subunits.
• FgRic8 may function upstream of cAMP signaling.

Proteins of the resistance to inhibitors of cholinesterase 8 (Ric8) group act as guanine nucleotide exchange factors (GEFs) and play important roles in regulating G-protein signaling in animals. In filamentous fungi, putative Ric8 orthologs have so far been identified in Magnaporthe oryzae, Neurospora crassa, Aspergillus nidulans and Aspergillus fumigatus. Here, we report the functional investigation of a potential RIC8 ortholog (FgRIC8) in the wheat head blight pathogen Fusarium graminearum. Targeted gene deletion mutants of FgRIC8 exhibited a significant reduction in vegetative growth, conidiation, pigment production as well as deoxynivalenol (DON) biosynthesis. Pathogenicity assays using a point-inoculated spikelet approach showed that the mutants were severely impaired in virulence on flowering wheat heads. Quantitative RT-PCR analysis revealed that genes encoding F. graminearum Gα (FgGpa1 and FgGpa3), Gβ (FgGpb1) and Gγ (FgGpg1) subunits were significantly down-regulated in Fgric8 mutants. Moreover, we showed that FgRic8 physically interacts with both FgGpa1 and FgGpa3, but not FgGpa2, in yeast two-hybrid assays. The intracellular cAMP levels in Fgric8 mutants were significantly decreased compared to the isogenic wild-type strain. Taken together, our results indicate that FgRic8 plays critical roles in fungal development, secondary metabolism and virulence in F. graminearum and may act as a regulator of G protein alpha subunits.