Target of rapamycin controls hyphal growth and pathogenicity through FoTIP4 in Fusarium oxysporum

Zinc finger transcription factor ZFP1 is associated with growth, conidiation, osmoregulation, and virulence in the Polygonatum kingianum pathogen Fusarium oxysporum

Rhizome rot is a destructive soil-borne disease of Polygonatum kingianum and adversely affects the yield and sustenance of the plant. Understanding how the causal fungus Fusarium oxysporum infects P. kingianum may suggest effective control measures against rhizome rot. In germinating conidia of infectious F. oxysporum, expression of the zinc finger transcription factor gene Zfp1, consisting of two C2H2 motifs, was up-regulated. To characterize the critical role of ZFP1, we generated independent deletion mutants (zfp1) and complemented one mutant with a transgenic copy of ZFP1 (zfp1 tZFP1). Mycelial growth and conidial production of zfp1 were slower than those of wild type (ZFP1) and zfp1 tZFP1. Additionally, a reduced inhibition of growth suggested zfp1 was less sensitive to conditions promoting cell wall and osmotic stresses than ZFP1 and zfp1 tZFP1. Furthermore pathogenicity tests suggested a critical role for growth of zfp1 in infected leaves and rhizomes of P. kingianum. Thus ZFP1 is important for mycelial growth, conidiation, osmoregulation, and pathogenicity in P. kingianum.

A New Insight into 6-Pentyl-2H-pyran-2-one against Peronophythora litchii via TOR Pathway

The litchi downy blight disease of litchi caused by Peronophythora litchii accounts for severe losses in the field and during storage. While ample quantitative studies have shown that 6-pentyl-2H-pyran-2-one (6PP) possesses antifungal activities against multiple plant pathogenic fungi, the regulatory mechanisms of 6PP-mediated inhibition of fungal pathogenesis and growth are still unknown. Here, we investigated the potential molecular targets of 6PP in the phytopathogenic oomycetes P. litchii through integrated deployment of RNA-sequencing, functional genetics, and biochemical techniques to investigate the regulatory effects of 6PP against P. litchii. Previously we demonstrated that 6PP exerted significant oomyticidal activities. Also, comparative transcriptomic evaluation of P. litchii strains treated with 6PP Revealed significant up-regulations in the expression profile of TOR pathway-related genes, including PlCytochrome C and the transcription factors PlYY1. We also noticed that 6PP treatment down-regulated putative negative regulatory genes of the TOR pathway, including PlSpm1 and PlrhoH12 in P. litchii. Protein-ligand binding analyses revealed stable affinities between PlYY1, PlCytochrome C, PlSpm1, PlrhoH12 proteins, and the 6PP ligand. Phenotypic characterization of PlYY1 targeted gene deletion strains generated in this study using CRISPR/Cas9 and homologous recombination strategies significantly reduced the vegetative growth, sporangium, encystment, zoospore release, and pathogenicity of P. litchii. These findings suggest that 6PP-mediated activation of PlYY1 expression positively regulates TOR-related responses and significantly influences vegetative growth and the virulence of P. litchii. The current investigations revealed novel targets for 6PP and underscored the potential of deploying 6PP in developing management strategies for controlling the litchi downy blight pathogen.

Constitutive activation of TORC1 signalling attenuates virulence in the cross-kingdom fungal pathogen Fusarium oxysporum

The filamentous fungus Fusarium oxysporum causes vascular wilt disease in a wide range of plant species and opportunistic infections in humans. Previous work suggested that invasive growth in this pathogen is controlled by environmental cues such as pH and nutrient status. Here we investigated the role of Target Of Rapamycin Complex 1 (TORC1), a global regulator of eukaryotic cell growth and development. Inactivation of the negative regulator Tuberous Sclerosis Complex 2 (Tsc2), but not constitutive activation of the positive regulator Gtr1, in F. oxysporum resulted in inappropriate activation of TORC1 signalling under nutrient-limiting conditions. The tsc2Δ mutants showed reduced colony growth on minimal medium with different nitrogen sources and increased sensitivity to cell wall or high temperature stress. Furthermore, these mutants were impaired in invasive hyphal growth across cellophane membranes and exhibited a marked decrease in virulence, both on tomato plants and on the invertebrate animal host Galleria mellonella. Importantly, invasive hyphal growth in tsc2Δ strains was rescued by rapamycin-mediated inhibition of TORC1. Collectively, these results reveal a key role of TORC1 signalling in the development and pathogenicity of F. oxysporum and suggest new potential targets for controlling fungal infections.

Cross-Talk and Multiple Control of Target of Rapamycin (TOR) in Sclerotinia sclerotiorum

Sclerotinia sclerotiorum is a necrotrophic phytopathogenic fungus that cross-talks with its hosts for control of cell-death pathways for colonization. Target of rapamycin (TOR) is a central regulator that controls cell growth, intracellular metabolism, and stress responses in a variety of eukaryotes, but little is known about TOR signaling in S. sclerotiorum. In this study, we identified a conserved TOR signaling pathway and characterized SsTOR as a critical component of this pathway. Hyphal growth of S. sclerotiorum was retarded by silencing SsTOR, moreover, sclerotia and compound appressoria formation were severely disrupted. Notably, pathogenicity assays of strains shows that the virulence of the SsTOR-silenced strains were dramatically decreased. SsTOR was determined to participate in cell wall integrity (CWI) by regulating the phosphorylation level of SsSmk3, a core MAP kinase in the CWI pathway. Importantly, the inactivation of SsTOR induced autophagy in S. sclerotiorum potentially through SsAtg1 and SsAtg13. Taken together, our results suggest that SsTOR is a global regulator controlling cell growth, stress responses, cell wall integrity, autophagy, and virulence of S. sclerotiorum. IMPORTANCE TOR is a conserved protein kinase that regulates cell growth and metabolism in response to growth factors and nutrient abundance. Here, we used gene silencing to characterize SsTOR, which is a critical component of TOR signaling pathway. SsTOR-silenced strains have limited mycelium growth, and the virulence of the SsTOR-silenced strains was decreased. Phosphorylation analysis indicated that SsTOR influenced CWI by regulating the phosphorylation level of SsSmk3. Autophagy is essential to preserve cellular homeostasis in response to cellular and environmental stresses. Inactivation of SsTOR induced autophagy in S. sclerotiorum potentially through SsAtg1 and SsAtg13. These findings further indicated that SsTOR is a global regulator of the growth, development, and pathogenicity of S. sclerotiorum in multiple ways.

Molecular Mechanism of Overcoming Host Resistance by the Target of Rapamycin Gene in Leptographium qinlingensis

Leptographium qinlingensis is a fungal symbiont of the Chinese white pine beetle (Dendroctonus armandi) and a pathogen of the Chinese white pine (Pinus armandii) that must overcome the terpenoid oleoresin defenses of host trees to invade and colonize. L. qinlingensis responds to monoterpene flow with abundant mechanisms that include the decomposing and use of these compounds as a nitrogen source. Target of Rapamycin (TOR) is an evolutionarily conserved protein kinase that plays a central role in both plants and animals through integration of nutrients, energies, hormones, growth factors and environmental inputs to control proliferation, growth and metabolism in diverse multicellular organisms. In this study, in order to explore the relationship between TOR gene and carbon sources, nitrogen sources, host nutrients and host volatiles (monoterpenoids) in L. qinlingensis, we set up eight carbon source treatments, ten nitrogen source treatments, two host nutrients and six monoterpenoids (5%, 10% and 20%) treatments, and prepared different media conditions. By measuring the biomass and growth rate of mycelium, the results revealed that, on the whole, the response of L. qinlingensis to nitrogen sources was better than carbon sources, and the fungus grew well in maltose (carbon source), (NH₄)₂C₂O₄ (inorganic nitrogen source), asparagine (organic nitrogen source) and P. armandii (host nutrient) versus other treatments. Then, by analyzing the relationship between TOR expression and different nutrients, the data showed that: (i) TOR expression exhibited negative regulation in response to carbon sources and host nutrition. (ii) The treatments of nitrogen sources and terpenoids had positively regulatory effects on TOR gene; moreover, the fungus was most sensitive to β-pinene and 3-carene. In conclusion, our findings reveal that TOR in L. qinlingensis plays a key role in the utilization of host volatiles as nutrient intake, overcoming the physical and chemical host resistances and successful colonization.

Salicylic acid fights against Fusarium wilt by inhibiting target of rapamycin signaling pathway in Fusarium oxysporum

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Isolating and sequencing the genome of F. oxysporum from potato tubers with dry rot symptoms.

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SA efficiently arrests hyphal growth, sporular production and pathogenicity of F. oxysporum.

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SA inhibits the activity of FoTORC1 via activating FoSNF1 in F. oxysporum.

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Transgenic potato plants with interference of FoTOR1 and FoSAH1 genes prevent the occurrence of Fusarium wilt.

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Providing insights SA into controlling various fungal diseases by targeting the SNF1-TORC1 pathway of pathogens.

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