UDP-Galactopyranose Mutase Mediates Cell Wall Integrity, Polarity Growth, and Virulence in Fusarium graminearum.

CHY1 is a zinc finger protein unique to microorganisms that was found to regulate polarized tip growth in Fusarium graminearum, an important pathogen of wheat and barley. To further characterize its functions, in this study we identified CHY1-interacting proteins by affinity purification and selected UDP-galactofuranose (Gal) mutase (UGMA) for detailed characterization, because UGMA and UDP-Gal are unique to fungi and bacteria and absent in plants and animals. The interaction between CHY1 and UGMA was confirmed by yeast two-hybrid assays. Deletion of UGMA in F. graminearum resulted in significant defects in vegetative growth, reproduction, cell wall integrity, and pathogenicity. Infection with the Δ mutant was restricted to the inoculated floret, and no vomitoxin was detected in kernels inoculated with the Δ strain. Compared to the wild type, the Δ mutant produced wide, highly branched hyphae with thick walls, as visualized by transmission electron microscopy. UGMA tagged with green fluorescent protein (GFP) mainly localized to the cytoplasm, consistent with the synthesis of Gal in the cytoplasm. The Δ mutant was more sensitive, while the Δ mutant was more tolerant, to cell wall-degrading enzymes. The growth of the Δ mutant nearly ceased upon caspofungin treatment. More interestingly, nocodazole treatment of the Δ strain attenuated its highly branched morphology, while caspofungin inhibited the degree of the twisted Δ mycelia, indicating that CHY1 and UGMA probably have opposite effects on cell wall architecture. In conclusion, UGMA is an important pathogenic factor that is specific to fungi and bacteria and required for cell wall architecture, radial growth, and caspofungin tolerance, and it appears to be a promising target for antifungal agent development. The long-term use of chemical pesticides has had increasingly negative impacts on the ecological environment and human health. Low-toxicity, high-efficiency and environmentally friendly alternative pesticides are of great significance for maintaining the sustainable development of agriculture and human and environmental health. Using fungus- or microbe-specific genes as candidate targets provides a good foundation for the development of low-toxicity, environmentally friendly pesticides. In this study, we characterized a fungus- and bacterium-specific UDP-galactopyranose mutase gene, , that contributes to the synthesis of the cell wall component Gal and is required for vegetative growth, cell wall integrity, deoxynivalenol (DON) production, and pathogenicity in F. graminearum. The deletion mutant exhibited increased sensitivity to caspofungin. These results demonstrate the functional importance of UGMA in F. graminearum, and its absence from mammals and higher plants constitutes a considerable advantage as a low-toxicity target for the development of new anti-Fusarium agents.