Molecular and functional characterization of a Rho GDP dissociation inhibitor in the filamentous fungus Tuber borchii

The bianchetto truffle (Tuber borchii) a lead-resistant ectomycorrhizal fungus increases Quercus cerris phytoremediation potential

Tuber borchii is a European edible truffle which forms ectomycorrhizas with several soft- and hardwood plants. In this article, the effects of high level of Pb on the in vitro growth of five T. borchii strains and the molecular mechanisms involved in Pb tolerance were studied. Moreover, the effects of the Pb treatment on T. borchii ectomycorrhizas and on the growth, element uptake and distribution in different organs of Quercus cerris seedlings were investigated. The results showed an extraordinary tolerance of T. borchii mycelium to Pb: all the tested strains were able to grow at Pb concentration over 4000 mg L^-1 . The mechanisms of tolerance seem related to Pb sequestration in the vacuole and its immobilization as crystal of Pb oxalate outside the hyphae rather than detoxification processes, considering the low expression of glutaredoxin and thioredoxin genes. T. borchii-Q. cerris mycorrhizas tolerate a soil concentration of Pb from 1869 to 4030 mg kg^-1 although, at these Pb concentrations, T. borchii showed a reduced ability to colonize roots. T. borchii mycorrhization increased the uptake of Pb by Q. cerris. Mycorrhization and Pb treatment also significantly influenced the uptake and translocation in the plant of other elements.

Bacteria-produced ferric exopolysaccharide nanoparticles as iron delivery system for truffles (Tuber borchii)

Iron exopolysaccharide nanoparticles were biogenerated during ferric citrate fermentation by Klebsiella oxytoca DSM 29614. Before investigating their effects on Tuber borchii ("bianchetto" truffle) mycelium growth and morphology, they were tested on human K562 cell line and Lentinula edodes pure culture and shown to be non-toxic. Using these nanoparticles as iron supplement, the truffles showed extremely efficient iron uptake of over 300 times that of a commercial product. This avoided morphological changes in T. borchii due to lack of iron during growth and, with optimum nanoparticle dosage, increased growth without cell wall disruption or alteration of protoplasmatic hyphal content, the nuclei, mitochondria, and rough endoplasmic reticula being preserved. No significant modifications in gene expression were observed. These advantages derive from the completely different mechanism of iron delivery to mycelia compared to commercial iron supplements. The present data, in fact, show the nanoparticles attached to the cell wall, then penetrating it non-destructively without damage to cell membrane, mitochondria, chromatin, or ribosome. Low dosage significantly improved mycelium growth, without affecting hyphal morphology. Increases in hyphal diameter and septal distance indicated a healthier state of the mycelia compared to those grown in the absence of iron or with a commercial iron supplement. These positive effects were confirmed by measuring fungal biomass as mycelium dry weight, total protein, and ergosterol content. This "green" method for biogenerating iron exopolysaccharide nanoparticles offers many advantages, including significant economic savings, without toxic effects on the ectomycorrhizal fungus, opening the possibility of using them as iron supplements in truffle plantations.

Centrosomal localization of RhoGDIβ and its relevance to mitotic processes in cancer cells

Rho GDP-dissociation inhibitors (RhoGDIs) are regulators of Rho family GTPases. RhoGDIβ has been implicated in cancer progression, but its precise role remains unclear. We determined the subcellular localization of RhoGDIβ and examined the effects of its overexpression and RNAi knockdown in cancer cells. Immunofluorescence staining showed that RhoGDIβ localized to centrosomes in human cancer cells. In HeLa cells, exogenous GFP-tagged RhoGDIβ localized to centrosomes and its overexpression caused prolonged mitosis and aberrant cytokinesis in which the cell shape was distorted. RNAi knockdown of RhoGDIβ led to increased incidence of monopolar spindle mitosis resulting in polyploid cells. These results suggest that RhoGDIβ has mitotic functions, including regulation of cytokinesis and bipolar spindle formation. The dysregulated expression of RhoGDIβ may contribute to cancer progression by disrupting these processes.

Effect of 300 mT static and 50 Hz 0.1 mT extremely low frequency magnetic fields on Tuber borchii mycelium

The present work aimed to investigate whether exposure to static magnetic field (SMF) and extremely low frequency magnetic field (ELF-MF) can induce biomolecular changes on Tuber borchii hyphal growth. Tuber borchii mycelium was exposed for 1 h for 3 consecutive days to a SMF of 300 mT or an ELF-MF of 0.1 mT 50 Hz. Gene expression and biochemical analyses were performed. In mycelia exposed to ELF-MF, some genes involved in hyphal growth, investigated using quantitative real-time polymerase chain reaction, were upregulated, and the activity of many glycolytic enzymes was increased. On the contrary, no differences were observed in gene expression after exposure to SMF treatment, and only the activities of glucose 6-phosphate dehydrogenase and hexokinase increased. The data herein presented suggest that the electromagnetic field can act as an environmental factor in promoting hyphal growth and can be used for applicative purposes, such as the set up of new in vitro cultivation techniques.

Ras and Rho small G proteins: insights from the Schizophyllum commune genome sequence and comparisons to other fungi

Unlike in animal cells and yeasts, the Ras and Rho small G proteins and their regulators have not received extensive research attention in the case of the filamentous fungi. In an effort to begin to rectify this deficiency, the genome sequence of the basidiomycete mushroom Schizophyllum commune was searched for all known components of the Ras and Rho signalling pathways. The results of this study should provide an impetus for further detailed investigations into their role in polarized hyphal growth, sexual reproduction and fruiting body development. These processes have long been the targets for genetic and cell biological research in this fungus.

Farnesol-induced apoptosis in Candida albicans

Farnesol, a precursor in the isoprenoid/sterol pathway, was recently identified as a quorum-sensing molecule produced by the fungal pathogen Candida albicans. Farnesol is involved in the inhibition of germination and biofilm formation by C. albicans and can be cytotoxic at certain concentrations. In addition, we have shown that farnesol can trigger apoptosis in mammalian cells via the classical apoptotic pathways. In order to elucidate the mechanism behind farnesol cytotoxicity in C. albicans, the response to farnesol was investigated, using proteomic analysis. Global protein expression profiles demonstrated significant changes in protein expression resulting from farnesol exposure. Among the downregulated proteins were those involved in metabolism, glycolysis, protein synthesis, and mitochondrial electron transport and the respiratory chain, whereas proteins involved in folding, protection against environmental and oxidative stress, actin cytoskeleton reorganization, and apoptosis were upregulated. Cellular changes that accompany apoptosis (regulated cell death) were further analyzed using fluorescent microscopy and gene expression analysis. The results indicated reactive oxygen species accumulation, mitochondrial degradation, and positive terminal deoxynucleotidyltransferase-mediated dUTP-biotin nick end labeling (TUNEL) in the farnesol-exposed cells concurrent with increased expression of antioxidant-encoding and drug response genes. More importantly, the results demonstrated farnesol-induced upregulation of the caspase gene MCA1 and the intracellular presence of activated caspases. In conclusion, this study demonstrated that farnesol promotes apoptosis in C. albicans through caspase activation, implying an important physiological role for farnesol in the fungal cell life cycle with important implications for adaptation and survival.