A network of transcription factors in complex with a regulating cell cycle cyclin orchestrates fungal oxidative stress responses.

BACKGROUND: Response to oxidative stress is universal in almost all organisms and the mitochondrial membrane protein, BbOhmm, negatively affects oxidative stress responses and virulence in the insect fungal pathogen, Beauveria bassiana. Nothing further, however, is known concerning how BbOhmm and this phenomenon is regulated. RESULTS: Three oxidative stress response regulating Zn2Cys6 transcription factors (BbOsrR1, 2, and 3) were identified and verified via chromatin immunoprecipitation (ChIP)-qPCR analysis as binding to the BbOhmm promoter region, with BbOsrR2 showing the strongest binding. Targeted gene knockout of BbOsrR1 or BbOsrR3 led to decreased BbOhmm expression and consequently increased tolerances to free radical generating compounds (H2O2 and menadione), whereas the ΔBbOsrR2 strain showed increased BbOhmm expression with concomitant decreased tolerances to these compounds. RNA and ChIP sequencing analysis revealed that BbOsrR1 directly regulated a wide range of antioxidation and transcription-associated genes, negatively affecting the expression of the BbClp1 cyclin and BbOsrR2. BbClp1 was shown to localize to the cell nucleus and negatively mediate oxidative stress responses. BbOsrR2 and BbOsrR3 were shown to feed into the Fus3-MAPK pathway in addition to regulating antioxidation and detoxification genes. Binding motifs for the three transcription factors were found to partially overlap in the promoter region of BbOhmm and other target genes. Whereas BbOsrR1 appeared to function independently, co-immunoprecipitation revealed complex formation between BbClp1, BbOsrR2, and BbOsrR3, with BbClp1 partially regulating BbOsrR2 phosphorylation. CONCLUSIONS: These findings reveal a regulatory network mediated by BbOsrR1 and the formation of a BbClp1-BbOsrR2-BbOsrR3 complex that orchestrates fungal oxidative stress responses.

Novel drimane-type sesquiterpenoids and nucleosides from the Helicoma septoconstrictum suppress the growth of ovarian cancer cells.

Four new drimane-type sesquiterpenoids and two new nucleoside derivatives (1-6), were isolated from the fungus Helicoma septoconstrictum. Their structures were determined based on the combination of the analysis of their HR-ESI-MS, NMR, ECD calculations data and acid hydrolysis. All the isolated compounds were detected for their bio-activities against MDA-MB-231, A549/DDP, A2780 and HepG2 cell lines. Helicoside C (4) exhibited superior cytotoxicity against the A2780 cell line with IC50 7.5 ± 1.5 µM. The analysis of reactive oxygen species (ROS) revealed that Helicoside C induced an increase in intracellular ROS. Furthermore, the flow cytometry and mitochondrial membrane potential (MMP) analyses unveiled that Helicoside C mediated mitochondrial-dependent apoptosis in A2780 cells. The western blotting test showed that Helicoside C could suppress the STAT3's phosphorylation. These findings offered crucial support for development of H. septoconstrictum and highlighted the potential application of drimane-type sesquiterpenoids in pharmaceuticals.

AaLaeA targets AaFla1 to mediate the production of antitumor compound in Alternaria alstroemeria.

Endophytic fungi are an important source of novel antitumor substances. Previously, we isolated an endophytic fungus, Alternaria alstroemeria, from the medicinal plant Artemisia artemisia, whose crude extracts strongly inhibited A549 tumor cells. We obtained a transformant, namely AaLaeAOE26 , which completely loses its antitumor activity due to overexpression of the global regulator AaLaeA. Re-sequencing analysis of the genome revealed that the insertion site was in the noncoding region and did not destroy any other genes. Metabolomics analysis revealed that the level of secondary antitumor metabolic substances was significantly lower in AaLaeAOE26 compared with the wild strain, in particular flavonoids were more downregulated according to the metabolomics analysis. A further comparative transcriptome analysis revealed that a gene encoding FAD-binding domain protein (Fla1) was significantly downregulated. On the other hand, overexpression of AaFla1 led to significant enhancement of antitumor activity against A549 with a sevenfold higher inhibition ratio than the wild strain. At the same time, we also found a significant increase in the accumulation of antitumor metabolites including quercetin, gitogenin, rhodioloside, liensinine, ginsenoside Rg2 and cinobufagin. Our data suggest that the global regulator AaLaeA negatively affects the production of antitumor compounds via controlling the transcription of AaFla1 in endophytic A. alstroemeria.

Application potential of biofertilizer-assisted Pennisetum giganteum in safe utilization of mercury-contaminated paddy fields.

High mercury (Hg) bioaccumulation in crops such as rice in Hg-contaminated areas presents a potential health hazard to humans and wildlife. To develop a safe alternative technique, bacillus-inoculated biofertilizer, citric acid, earthworms, and selenium-modified activated clay were compared for their ability to regulate Hg bioaccumulation in Pennisetum giganteum (P. giganteum). This biofertilizer significantly increased Bacillus sp. abundance in the soil by 157.12%, resulting in the removal of 27.52% of water-soluble Hg fractions through volatilization and adsorption mechanisms. The variation in bioavailable Hg in the soil significantly reduced the total Hg concentration in P. giganteum young leaves, old leaves, stems, and roots of P. giganteum by 74.14%, 48.08%, 93.72%, and 50.91%, respectively (p < 0.05), which is lower than the Chinese feed safety standard (100 ng g-1). The biofertilizer inhibitory potential was highly consistent with that of the selenium-modified activated clay. Biofertilizers significantly reduced the methylmercury concentration in various P. giganteum tissues (p < 0.05), whereas selenium-modified activated clay failed to achieve a comparable effect. This biofertilizer-assisted planting pattern can achieve an economic income quadruple that of the rice planting pattern in the Hg-contaminated paddy fields. Because of its significant environmental and financial applications, the biofertilizer-assisted planting pattern is expected to replace Hg-contaminated paddy fields.

Nanoemulsion of the Essential Oil from Blumea balsamifera (L.) DC. and Its Effect on Trauma Repair.

The essential oil, extracted from the Hmong medicine Blumea balsamifera (L.) DC. (BBO), is a purely natural wound repair agent. Its application has, however, been restricted due to its low solubility and high volatility properties. In this study, we have developed a nanoemulsion formulation to improve the characteristics of BBO. The particle size of the nanoemulsion was normally distributed, and 71% of its range was concentrated between 10-100 nm, with an average particle size of 62.8 nm and an encapsulation rate of 98%. After 7 days of application, the wound healing rate of the BBO nanoemulsion (BBO-NE) group was 1.5 times higher than that of the normal BBO group. Along with histological observations, nanoemulsion formulation has been demonstrated to significantly improve the efficacy of BBO for wound repair. In addition, inflammation-related TLR4, CD14 and IRAK-1 gene transcript levels were significantly reduced after the administration of BBO-NE compared to the BBO group, with downregulation of 47.8%, 35.7% and 57.8%, respectively, while the secretion of pro-inflammatory factors IL-6 and TNF-α was also significantly reduced by 83.8% and 32.7%, respectively, in the nanoformulation administration (BBO-NE) group compared to the BBO group. In contrast, the anti-inflammatory factor IL-10 was significantly increased by 4.2-fold. It was further found that the drug penetration per unit area increased significantly 6.30% to 19.5% at different time points after the application of the BBO-NE compared to the BBO. In conclusion, nano-formulation enhanced the drug penetration of the BBO, reduced inflammatory factors, increased the level of anti-inflammatory factors, and promoted collagen deposition, thereby accelerating wound repair.

Sterol Regulatory Element-Binding Protein, BbSre1, Controls Oxidative Stress Response, Peroxisome Division, and Lipid Homeostasis in an Insect Fungal Pathogen.

Sterol regulatory element-binding protein, Sre1, regulates sterol biosynthesis, lipid metabolism, hypoxia adaptation, and virulence in some fungi, even though its roles are varied in fungal species. However, few studies report its other functions in fungi. Here, we report novel roles of Sre1 homolog, BbSre1, in the insect fungal pathogen, Beauveria bassiana, that regulates oxidative stress response, peroxisome division, and redox homeostasis. The gene disruption stain showed increased sensitivity to oxidative stress, which was in line with oxidative stress-induced-BbSre1 nuclear import and control of antioxidant and detoxification-involved genes. The gene mutation also inhibited peroxisome division, affected redox homeostasis, and impaired lipid/fatty acid metabolism and sterol biosynthesis, which was verified by downregulation of their associated genes. These data broaden our understanding of role of Sre1, which regulates peroxisome division, antioxidant, and detoxification-involved genes for control of redox homeostasis and oxidative stress response that links to lipid/fatty acid metabolism and sterol biosynthesis.

Endophytic fungus Biscogniauxia petrensis produces antibacterial substances.

Widespread drug resistance and limited antibiotics challenge the treatment of pathogenic bacteria, which leads to a focus on searching for new antimicrobial lead compounds. We found the endophytic fungus Biscogniauxia petrensis MFLUCC14-0151 from the medicinal plant Dendrobium harveyanum had antibacterial activity for the first time. This work aimed to reveal the capacity of Biscogniauxia petrensis MFLUCC14-0151 against foodborne pathogenic bacteria and identify its bioactive substances. Bioassay-guided isolation led to the discovery of six infrequent active monomers, including (10R)-Xylariterpenoid B (1), Xylariterpenoid C (2), Tricycloalternarene 1b (3), Tricycloalternarene 3b (4), Funicin (5) and Vinetorin (6) from MFLUCC14-0151 for the first time. The results of antibacterial tests showed that (10R)-Xylariterpenoid B and Xylariterpenoid C exhibited inhibitory activities against Streptococcus agalactiae with MIC values ranging from 99.21 to 100.00 µM, and against Streptococcus aureus with MIC values ranging from 49.60 to 50.00 µM. Tricycloalternarene 1b and Tricycloalternarene 3b showed inhibitory effects on Streptococcus agalactiae with MIC values ranging from 36.13 to 75.76 µM. Unexpectedly, Funicin and Vinetorin exhibited remarkable antagonistic activities against Streptococcus agalactiae with MIC values of 10.35 and 10.21 µM, respectively, and against Streptococcus aureus with MIC values of 5.17 and 20.42 µM, respectively. In conclusion, we suggest that the isolated compounds Funicin and Vinetorin may be promising lead compounds for natural antibacterial agents.

A Novel Effector FlSp1 Inhibits the Colonization of Endophytic Fusarium lateritium and Increases the Resistance to Ralstonia solanacearum in Tobacco.

Effectors are crucial for the interaction between endophytes and their host plants. However, limited attention has been paid to endophyte effectors, with only a few reports published. This work focuses on an effector of Fusarium lateritium, namely FlSp1 (Fusarium-lateritium-Secreted-Protein), a typical unknown secreted protein. The transcription of FlSp1 was up-regulated after 48 h following fungal inoculation in the host plant, i.e., tobacco. The inactivation of FlSp1 with the inhibition rate decreasing by 18% (p < 0.01) resulted in a remarkable increase in the tolerance of F. lateritium to oxidative stress. The transient expression of FlSp1 stimulated the accumulation of reactive oxygen species (ROS) without causing plant necrosis. In comparison with the wild type of F. lateritium (WT), the FlSp1 mutant of the F. lateritium plant (ΔFlSp1) reduced the ROS accumulation and weakened the plant immune response, which resulted in significantly higher colonization in the host plants. Meanwhile, the resistance of the ΔFlSp1 plant to the pathogenic Ralstonia solanacearum, which causes bacterial wilt, was increased. These results suggest that the novel secreted protein FlSp1 might act as an immune-triggering effector to limit fungal proliferation by stimulating the plant immune system through ROS accumulation and thus balance the interaction between the endophytic fungi and their host plants.

New Spirostane from a Fungus Neohelicomyces hyalosporus and Its Bioactivity.

A new spirostane, namely neohelicomyine B (1), together with six known steroids (2-7) were isolated from the fermentation of fungus Neohelicomyces hyalosporus. The structures of these compounds were elucidated by extensive analyses of spectroscopic methods including 1D and 2D NMR and HR-ESI-MS. The absolute configuration of 1 was confirmed by single-crystal X-ray diffraction. The bioactivities of compounds 1-7 were evaluated using cellular assays. Compound 1 displayed moderate cytotoxicity against HepG2 cells (hepatoma cells) with IC50 value of 8.4±2.1 µM. Compound 7 also exhibited cytotoxic activity against HepG2 cells with the IC50 value of 3.0±0.2 µM.

New Guaiane-Type Sesquiterpenoids Biscogniauxiaols A-G with Anti-Fungal and Anti-Inflammatory Activities from the Endophytic Fungus Biscogniauxia Petrensis.

Seven undescribed guaiane-type sesquiterpenoids named biscogniauxiaols A-G (1-7) were isolated from the endophytic fungus Biscogniauxia petrensis on Dendrobium orchids. Their structures were determined by extensive spectroscopic analyses, electronic circular dichroism (EC) and specific rotation (SR) calculations. Compound 1 represented a new family of guaiane-type sesquiterpenoids featuring an unprecedented [5/6/6/7] tetracyclic system. A plausible biosynthetic pathway for compounds 1-7 was proposed. The anti-fungal, anti-inflammatory and multidrug resistance reversal activities of the isolates were evaluated. Compounds 1, 2 and 7 exhibited potent inhibitory activities against Candida albicans with MIC values ranging from 1.60 to 6.30 µM, and suppressed nitric oxide (NO) production with IC50 ranging from 4.60 to 20.00 µM. Additionally, all compounds (100 µg/mL) enhanced the cytotoxicity of cisplatin in cisplatin-resistant non-small cell lung cancer cells (A549/DDP). This study opened up a new source for obtaining bioactive guaiane-type sesquiterpenoids and compounds 1, 2, and 7 were promising for further optimization as multifunctional inhibitors for anti-fungal (C. albicans) and anti-inflammatory purposes.

A Saprophytic Fungus Tubeufia rubra Produces Novel Rubracin D and E Reversing Multidrug Resistance in Cancer Cells.

Two new (1, 2 viz Rubracin D and E) and sixteen known Glyceroglycolipids (3-18) in the saprophytic fungus Tubeufia rubra (PF02-2) from decaying wood in freshwater habitat were isolated and identified. Their chemical structures were elucidated via means of the extensive spectroscopic analyses of NMR, HR-ESI-MS and UV spectra, as well as comparison with literature data. The new compounds were assayed for the reversal activity of multidrug resistance (MDR) on MCF-7/ADM, K562/ADM and A549/ADM cell lines, and both compounds 1 and 2 reversed MDR in the three resistant cancer cell lines with concentration dependence. In the assay on K562/ADM, both new compounds had been proved to have remarkable MDR reversal effects, which were higher than those of the positive control viz Verapamil (Vrp). Meanwhile, in the assay on A549/ADM, compound 1 displayed significant MDR reversal effects, which were also higher than those of Vrp at certain concentrations. Furthermore, the Western blot assay proved that both new compounds reversed the MDR in the resistant cancer cell line viz MCF-7/ADM by inhibiting the overexpression of P-glycoprotein. This is the first report that the Glyceroglycolipids isolated firstly from the fungal genus Tubeufia reversed MDR in resistant cancer cells.

A new alkaloid derivative from the saprophytic fungus Neohelicomyces hyalosporus PF11-1.

A new alkaloid, neohelicomyine A (1), along with two known alkaloids (2-3), were isolated from the fermentation of Neohelicomyces hyalosporus PF11-1. The structures of these compounds were elucidated by extensive analyses of spectroscopic methods including 1 D and 2 D NMR, HRESIMS and ECD. The bioactivities of all compounds were evaluated using cellular assays, and compounds 2 and 3 displayed moderate cytotoxicities against human cancer (A549, TCA, RD) cells with IC50 values of 26-87 µg/mL.

Global regulatory factor AaLaeA upregulates the production of antitumor substances in the endophytic fungus Alternaria alstroemeria.

The global regulatory factor LaeA has been shown to be involved in the biosynthesis of secondary metabolites in various fungi. In a previous work, we isolated an endophytic fungus from Artemisia annua, and its extract had a significant inhibitory effect on the A549 cancer cell line. Phylogenetic analysis further identified the strain as Alternaria alstroemeria. Overexpression of AalaeA gene resulted in significantly increased antitumor activity of this strain's extract. The 3-(4, 5- dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide assay results showed that the inhibition rate of the AalaeAOE29 mutant extract on A549 cancer cells was significantly higher than that of the WT extract, as the IC50 decreased from 195.0 to 107.4 µg/ml, and the total apoptosis rate was enhanced. Overexpression of the AalaeA gene significantly increased the contents of myricetin, geraniol, ergosterol, and 18 other antitumor compounds as determined by metabolomic analysis. Transcriptomic analysis revealed significant changes in 95 genes in the mutant strain, including polyketide synthases, nonribosomal peptide synthases, cytochrome P450s, glycosyltransferases, acetyl-CoA acetyltransferases, and others. These results suggested that AaLaeA mediated the antitumor activity of the metabolites in A. alstroemeria by regulating multiple metabolic pathways.

Global regulatory factor VeA upregulates the production of antitumor substances in endophytic Fusarium solani.

A number of studies have demonstrated that endophytic fungi have the potential to produce antitumor active substances with novel structures and significant activities. In our previous studies, we isolated a Fusarium strain from the stem of the medicinal plant Nothapodytes pittosporoides (Oliv.). In this study, we identified this strain as Fusarium solani and found that its crude extract has significant antitumor activity against human alveolar adenocarcinoma cells (A549). We overexpressed the global regulatory factor VeA in F. solani (VeAOE), resulting in a significant increase in antitumor activity. The MTT assay results showed that the inhibition rate of the VeAOE mutant extract on A549 cancer cells was significantly higher than that of the WT extract, as the IC50 decreased from 369.22 to 285.89 µg/mL, and the apoptosis ratio was significantly increased by approximately 4.86-fold. In VeAOE, accumulation of alkaloids, terpenoids, carboxylic acid derivatives, phenols and flavonoid metabolites with potential antitumor activity was significantly increased compared with WT based on metabolomic analysis. Additionally, transcriptome analysis found that the expression patterns of 48 genes related to antitumor activity were significantly changed in VeAOE, mainly involving glycosyl hydrolases, the Zn(2)-Cys(6) class, cytochrome P450 monooxygenase, 3-isopropylmalate dehydratase, and polyketide synthases. These results suggested that VeA mediated the antitumor activity of the metabolites in F. solani HB1-J1 by regulating multiple metabolic pathways.

Overexpression of the global regulator FnVeA upregulates antitumor substances in endophytic Fusarium nematophilum.

The special niche of endophytic fungi promotes their potential to produce antitumor compounds with novel structure and significant bioactivity for screening of new antitumor drugs. In our previous studies, we isolated a Fusarium strain from the roots of the medicinal plant Nothapodytes pittosporoides and identified it as Fusarium nematophilum. We found that the crude extract of F. nematophilum had significant antitumor activity on A549 cancer cells, and overexpressing the global regulatory factor FnVeA (the VeA gene of the fungus F. nematophilum) resulted in a significant increase in the antitumor activity, which was approximately fivefold higher than wild strain for relative inhibition rate. In FnVeAOE, the accumulation of indole, alkene, alkaloid, steroid, and flavonoid metabolites with potential antitumor activity was significantly upregulated compared with wild type via metabolomic analysis. Moreover, the transcriptome analysis showed that 134 differential genes were considered to be closely related to the biosynthesis of antitumor substances, of which 59 differential genes were considered as candidate key genes, and related to tryptophan dimethylallyltransferase, cytochrome P450 monooxygenase, polyketide synthases, and transcription factors. Taken together, we suggest that FnVeA may regulate the biosynthesis of antitumor substances by mediating the expression of genes related to secondary metabolic pathways in F. nematophilum.

Participation of a MADS-box transcription factor, Mb1, in regulation of the biocontrol potential in an insect fungal pathogen.

The cell wall is crucial for fungal growth, proliferation and interaction with the environment and host. Understanding the regulatory mechanism of cell wall integrity may help with improvement of fungal biocontrol agents. Here, a putative target of the cell wall integrity pathway-involved Slt2 MAP kinase, Mb1, an orthologue of MADS-box transcription factor Rlm1, was characterized in an economically important insect fungal pathogen, Beauveria bassiana. Mb1 disruption mutant (ΔMb1) displayed reduced growth and increased conidial production on minimal medium but not on rich-nutrient media, which is different from ΔSlt2 to a great extent. Loss of Mb1 resulted in a significant increase in sensitivity to cell wall-perturbing agents (Congo red and calcofluor white), with alteration in cell composition that was inconsistent with ΔSlt2 strain, including increased chitin content and reduced chitin-binding ß-1, 3/1,6-glucan levels in the absence of any stress. Transcription levels of 15 chitin synthesis and metabolism-associated and 17 Pkc1-Slt2 CWI (cell wall integrity) pathway, glucan synthesis, and cell wall remodeling enzyme synthesis-involved genes were significantly increased and repressed in ΔMb1 strain, respectively, some of which were verified to be the targets of Mb1. Insect bioassays revealed decreased virulence for the ΔMb1 strain in both topical and intrahemocoel injection assays. Our results demonstrated that Mb1 control fungal biocontrol potential-associated traits, including growth, conidiation and cell wall integrity, in B. bassiana. The difference of Mb1 and Slt2 in contribution to cell wall integrity is discussed.

The fungal mitochondrial membrane protein, BbOhmm, antagonistically controls hypoxia tolerance.

Adaptation to low-oxygen (LO) environment in host tissues is crucial for microbial pathogens, particularly fungi, to successfully infect target hosts. However, the underlying mechanisms responsible for hypoxia tolerance in most pathogens are poorly understood. A mitochondrial protein, BbOhmm, is demonstrated to limit oxidative stress resistance and virulence in the insect fungal pathogen, Beauveria bassiana. Here, we found that BbOhmm negatively affected hypoxic adaptation in the insect haemocoel while regulating respiration-related events, heme synthesis and mitochondrial iron homeostasis. A homologue of the mammalian sterol regulatory element-binding proteins (SREBPs), BbSre1, was shown to be involved in BbOhmm-mediated LO adaptation. Inactivation of BbSre1 resulted in a significant increase in sensitivity to hypoxic and oxidative stress. Similar to ΔBbOhmm, ΔBbSre1 or the ΔBbOhmmΔBbSre1 double mutant accumulated high levels of heme and mitochondrial iron, regulating the similar pathways during hypoxic stress. BbSre1 transcriptional activity and nuclear import were repressed in ΔBbOhmm cells and affected by intracellular reactive oxygen species (ROS) and oxygen levels. These findings have led to a new model in which BbOhmm affects ROS homeostasis in combination with available oxygen to control the transcriptional activity of BbSre1, which in turn mediates LO adaptation by regulating mitochondrial iron homeostasis, heme synthesis and respiration-implicated genes.

MADS-box transcription factor Mcm1 controls cell cycle, fungal development, cell integrity and virulence in the filamentous insect pathogenic fungus Beauveria bassiana.

MADS-box transcription factor Mcm1 plays crucial roles in regulating mating processes and pathogenesis in some fungi. However, its roles are varied in fungal species, and its function remains unclear in entomopathogenic fungi. Here, Mcm1 orthologue, Bbmcm1, was characterized in a filamentous entomopathogenic fungus, Beauveria bassiana. Disruption of Bbmcm1 resulted in a distinct reduction in growth with abnormal conidiogenesis, and a significant decrease in conidial viability with abnormal germination. ΔBbmcm1 displayed impaired cell integrity, with distorted cell wall structure and altered cell wall component. Abnormal cell cycle was detected in ΔBbmcm1 with longer G2 /M phase but shorter G1 /G0 and S phases in unicellular blastospores, and sparser septa in multicellular hyphae, which might be responsible for defects in development and differentiation due to the regulation of cell cycle-involved genes, as well as the corresponding cellular events-associated genes. Dramatically decreased virulence was examined in ΔBbmcm1, with impaired ability to escape haemocyte encapsulation, which was consistent with markedly reduced cuticle-degrading enzyme production by repressing their coding genes, and downregulated fungal effector protein-coding genes, suggesting a novel role of Mcm1 in interaction with host insect. These data indicate that Mcm1 is a crucial regulator of development, cell integrity, cell cycle and virulence in insect fungal pathogens.

An aldo-keto reductase, Bbakr1, is involved in stress response and detoxification of heavy metal chromium but not required for virulence in the insect fungal pathogen, Beauveria bassiana.

The aldo-keto reductases (AKRs) belong to the NADP-dependent oxidoreductase superfamily, which play important roles in various physiological functions in prokaryotic and eukaryotic organisms. However, many AKR superfamily members remain uncharacterized. Here, a downstream target gene of the HOG1 MAPK pathways coding for an aldo-keto reductase, named Bbakr1, was characterized in the insect fungal pathogen, Beauveria bassiana. Bbakr1 expression increased in response to osmotic and salt stressors, and oxidative and heavy metal (chromium) stress. Deletion of Bbakr1 caused a reduction in conidiation, as well as delayed conidial germination. ΔBbakr1 displayed increased sensitivity to osmotic/high-salt stress with decreased compatible solute accumulation. In addition, the mutant was more sensitive to high concentrations of the heavy metal, chromium, and to oxidative stress than the wild type cells, with impaired ability to detoxify active aldehyde that might accumulate due to lipid peroxidation. However, over-expressing Bbakr1 in either the wild type strain or a ΔBbhog1 background did not cause any obvious changes in phenotypes as compared to their controls. Little effect on virulence was seen for either the ΔBbakr1 or overexpression strains in insect bioassays via cuticle infection or intrahemocoel injection assays, suggesting that Bbakr1 is not required for virulence.

Comparative transcriptome and gene co-expression network analysis reveal genes and signaling pathways adaptively responsive to varied adverse stresses in the insect fungal pathogen, Beauveria bassiana.

Sensing, responding, and adapting to the surrounding environment are crucial for all living organisms to survive, proliferate, and differentiate in their biological niches. Beauveria bassiana is an economically important insect-pathogenic fungus which is widely used as a biocontrol agent to control a variety of insect pests. The fungal pathogen unavoidably encounters a variety of adverse environmental stresses and defense response from the host insects during application of the fungal agents. However, few are known about the transcription response of the fungus to respond or adapt varied adverse stresses. Here, we comparatively analyzed the transcriptome of B. bassiana in globe genome under the varied stationary-phase stresses including osmotic agent (0.8 M NaCl), high temperature (32 °C), cell wall-perturbing agent (Congo red), and oxidative agents (H2O2 or menadione). Total of 12,412 reads were obtained, and mapped to the 6767 genes of the B. bassiana. All of these stresses caused transcription responses involved in basal metabolism, cell wall construction, stress response or cell rescue/detoxification, signaling transduction and gene transcription regulation, and likely other cellular processes. An array of genes displayed similar transcription patterns in response to at least two of the five stresses, suggesting a shared transcription response to varied adverse stresses. Gene co-expression network analysis revealed that mTOR signaling pathway, but not HOG1 MAP kinase pathway, played a central role in regulation the varied adverse stress responses, which was verified by RNAi-mediated knockdown of TOR1. Our findings provided an insight of transcription response and gene co-expression network of B. bassiana in adaptation to varied environments.