Small GTPase FoSec4-Mediated Protein Secretion Is Important for Polarized Growth, Reproduction and Pathogenicity in the Banana Fusarium Wilt Fungus Fusarium odoratissimum

Roles of the Sec2p Gene in the Growth and Pathogenicity Regulation of Aspergillus fumigatus

Aspergillus fumigatus (A. fumigatus) is a filamentous fungus that causes invasive aspergillosis in immunocompromised individuals. Regulating fungal growth is crucial for preventing disease development. This study found that deleting the guanine nucleotide exchange factor Sec2p gene led to slower A. fumigatus growth and reduced the fungal burden and mortality of infected mice. However, the mechanism by which this gene affects A. fumigatus growth and pathogenicity remains unclear. Transmission electron microscopy revealed that the vacuoles of the gene knockout strain ΔSec2p accumulated more autophagosomes, indicating inhibition of autophagosome degradation. When phenylmethylsulfonyl fluoride was applied to inhibit autophagosome degradation, the ΔSec2p strain produced fewer autophagosomes; the ΔSec2p autophagy pathway was inhibited, affecting A. fumigatus' nutrient homeostasis and growth. Unlike the wild type, the ΔSec2p strain showed strong resistance to cell wall stress. When exposed to caspofungin, Sec2p negatively regulated the expression of cell wall integrity (CWI) pathway genes and participated in the cell wall stress response of A. fumigatus. Furthermore, this gene positively regulated the autophagy pathway and enhanced CWI pathway gene expression to respond to rapamycin-induced autophagy. In summary, Sec2p positively regulated the autophagy pathway; it negatively regulated the CWI pathway during cell wall stress, coordinating the growth and pathogenicity of A. fumigatus.

Rho4 interacts with BbGDI and is essential for the biocontrol potential of Beauveria bassiana by maintaining intracellular redox homeostasis

Rho4 is a member of the Rho-family small GTPases. In this study, we revealed the function of Rho4 and explored its mechanism involved in intracellular redox homeostasis in Beauveria bassiana, one of the most widely utilized filamentous entomopathogenic fungi. The disruption of Rho4 in B. bassiana resulted in significant phenotypic changes, such as fungal virulence, growth rate on different media, thermotolerance, germination, and conidiation. Integrated analysis of proteomic and transcriptomic data unveiled differential expression patterns of various redox-related genes and proteins in Δrho4, including the down-regulation of GST shown in proteomic and transcriptomic data, and the down-regulated gene expression levels of NOX, SOD, CAT, and GR in the transcriptome. Based on the bi-omics analysis, we focused on the impact of Rho4 in maintaining intracellular redox homeostasis. A decreased ROS content observed in Δrho4 might be attributed to the reduced NOX activity, which subsequently affects the GSH-producing/consuming metabolisms, with the attenuated activities of GR and GST. The imbalanced redox homeostasis also resulted in the reduced enzyme activities of SOD and CAT. Exogenous oxides could partially complement the ROS level and rescue the growth defect in Δrho4 to a certain extent. Besides, BbGDI was initially identified as an interacting protein of Rho4 in entomopathogenic fungi. Our results provide a comprehensive understanding of the function and regulating mechanism of Rho4 in B. bassiana.

Two distinct SNARE complexes mediate vesicle fusion with the plasma membrane to ensure effective development and pathogenesis of Fusarium oxysporum f. sp. cubense

SNAREs (soluble N-ethylmaleimide-sensitive factor attachment protein receptors) facilitate docking and fusion of vesicles with their target membranes, playing a crucial role in vesicle trafficking and exocytosis. However, the spatial assembly and roles of plasma membrane (PM)-associated SNAREs in phytopathogen development and pathogenicity are not clearly understood. In this study, we analysed the roles and molecular mechanisms of PM-associated SNARE complexes in the banana Fusarium wilt fungus Fusarium oxysporum f. sp. cubense tropical race 4 (FocTR4). Our findings demonstrate that FocSso1 is important for the fungal growth, conidiation, host penetration and colonization. Mechanistically, FocSso1 regulates protein secretion by mediating vesicle docking and fusion with the PM and hyphal apex. Interestingly, a FocSso1-FocSec9-FocSnc1 complex was observed to assemble not only at the fungal PM but also on the growing hyphal apex, facilitating exocytosis. FocSso2, a paralogue of FocSso1, was also found to form a ternary SNARE complex with FocSec9 and FocSnc1, but it mainly localizes to the PM in old hyphae. The functional analysis of this protein demonstrated that it is dispensable for the fungal growth but necessary for host penetration and colonization. The other subunits, FocSec9 and FocSnc1, are involved in the fungal development and facilitate host penetration. Furthermore, FocSso1 and FocSnc1 are functionally interdependent, as loss of FocSso1 leads to mis-sorting and degradation of FocSnc1 in the vacuole and vice versa. Overall, this study provides insight into the formation of two spatially and functionally distinct PM SNARE complexes and their involvement in vesicle exocytosis to regulate development and pathogenicity of FocTR4.

Special Issue "Genomics of Fungal Plant Pathogens"

Plant diseases can be classified according to pathogenic organisms, and 70-80% of them are fungal diseases [...].