The NDR kinase-MOB complex FgCot1-Mob2 regulates polarity and lipid metabolism in Fusarium graminearum.

Members of the NDR (nuclear Dbf2-related) protein-kinase family are essential for cell differentiation and polarized morphogenesis. However, their functions in plant pathogenic fungi are not well understood. Here, we characterized the NDR kinase FgCot1 and its activator FgMob2 in Fusarium graminearum, a major pathogen causing Fusarium head blight (FHB) in wheat. FgCot1 and FgMob2 formed a NDR kinase-MOB protein complex. Localization assays using FgCot1-GFP or FgMob2-RFP constructs showed diverse subcellular localizations, including cytoplasm, septum, nucleus and hyphal tip. ΔFgcot1 and ΔFgmob2 exhibited serious defects in hyphal growth, polarity, fungal development and cell wall integrity as well as reduced virulence in planta. In contrast, lipid droplet accumulation was significantly increased in these two mutants. Phosphorylation of FgCot1 at two highly conserved residues (S462 and T630) as well as five new sites synergistically contributed its role in various cellular processes. In addition, non-synonymous mutations in two MAPK (mitogen-activated protein kinase) proteins, FgSte11 and FgGpmk1, partially rescued the growth defect of ΔFgmob2, indicating a functional link between the FgCot1-Mob2 complex and the FgGpmk1 signalling pathway in regulating filamentous fungal growth. These results indicated that the FgCot1-Mob2 complex is critical for polarity, fungal development, cell wall organization, lipid metabolism and virulence in F. graminearum.

System-wide characterization of subtilases reveals that subtilisin-like protease FgPrb1 of Fusarium graminearum regulates fungal development and virulence.

Subtilases represent the second largest subfamily of serine proteases, and are important for various biological processes. However, the biological function of subtilases has not been systematically characterized in plant pathogens. In present study, 32 subtilases were identified in the genome of wheat scab fungus Fusarium graminearum, a devastating cereal plant pathogen. Deletion mutants of each subtilase were obtained and functionally characterized. Among them, the deletion of FgPrb1 resulted in greatly reduced virulence of F. graminearum. The regulatory mechanisms of FgPrb1 in virulence were investigated in details. Our results showed that the loss of FgPrb1 led to defects in deoxynivalenol (DON) production, responses to environmental stimuli, and lipid metabolism. Additionally, we found that FgPrb1 was involved in autophagy regulation. Taken together, the systematic functional characterization of subtilases showed that the FgPrb1 of F. graminearum is critical for plant infection by regulating multiple different cellular processes.

The endocytic cargo adaptor complex is required for cell-wall integrity via interacting with the sensor FgWsc2B in Fusarium graminearum.

AP2 is a heterotetrameric clathrin adaptor complex that owns important roles in vesicle generation and cargo recognition. Cell-wall integrity (CWI) pathway is essential for fungal development, virulence, and adaptation to environment stresses. To date, the relationship between AP2 and CWI is largely unknown in phytopathogenic fungi. In this study, we identified the adaptor complex FgAP2 in Fusarium graminearum. The biological function analysis showed that FgAP2 complex contains FgAP2α, FgAP2ß, FgAP2σ, and FgAP2µ, and the subunit FgAP2µ, which is required for hyphal growth, conidiation, CWI, and virulence. Yeast two-hybrid showed that FgAP2µ interacts with the CWI sensor FgWsc2B. Consistently, western blotting analysis revealed that FgWsc2B positively regulates phosphorylation of FgMgv1, the MAP kinase of CWI. Moreover, the FgWsc2B deletion mutant exhibited defects in hyphal growth, virulence, and response to CWI damaging agents. Taken together, our data indicated that FgAP2µ is involved in CWI and virulence via interacting with FgWsc2B in F. graminearum.