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Reductive assimilation pathway involves ferric reductase and ferrous iron transporter, which is integral for fungal iron acquisition. A family of ferric reductase-like proteins has been functionally characterized in the filamentous entomopathogenic fungus Beauveria bassiana. In this investigation, two ferrous iron transporter-like proteins (Ftr) were functionally annotated in B. bassiana. BbFtr1 and BbFtr2 displayed high similarity in structure and were associated with the plasma and nuclear membrane. Their losses had no negatively influence on fungal growth on various nutrients and development under the iron-replete condition. Single mutants of BbFTR1 and BbFTR2 displayed the iron-availability dependent developmental defects, and double mutant exhibited the significantly impaired developmental potential under the iron-limited conditions. In insect bioassay, the double mutant also showed the weaker virulence than either of two single disruption mutants. These results suggested that two ferrous iron transporter-like proteins function independently in fungal physiologies under the iron-deficient condition. Intriguingly, a bZIP transcription factor BbHapX was required for expression of BbFTR1 and BbFTR2 under iron-depleted conditions. This study enhances our understanding of the iron uptake system in the filamentous entomopathogenic fungi., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Inc. All rights reserved.)

Sterol carrier protein 2 (SCP2) represents a family of proteins binding a variety of lipids and plays essential roles in cellular physiology. However, its physiological roles are largely unknown in filamentous fungi. In this study, we functionally characterized an orthologous Scp2 gene in the filamentous insect pathogenic fungus Beauveria bassiana (BbScp2). BbScp2 was verified to be a peroxisomal protein and displayed different affinities to various lipids, with strong affinity to palmitic acid (PA) and ergosterol (ES). No significant binding activity was detected between protein and oleic acid (OA) or linoleic acid (LA). Ablation of BbScp2 did not cause significant effects on fungal growth on various carbon sources, but resulted in a modest reduction in conidial (49%) and blastospore yield (45%). In addition, exogenous lipids could recover the defectives in conidiation of ΔBbScp2 mutant strain. BbScp2 was required for the cytomembrane functionality in germlings, and its loss resulted in a more significant decrease in virulence indicated by cuticle infection assay than intrahemocoel injection assay. Our findings indicate that Scp2 links the lipid trafficking to the asexual differentiation and virulence of B. bassiana., (Copyright © 2021 Elsevier Inc. All rights reserved.)

Beauveria bassiana is a well-known entomopathogenic fungus that parasitizes on a variety of insect species. Glucan in the cell wall of B. bassiana plays a crucial role in its structure and growth and is also involved in the activation of the host insect's immune system. Glucan biosynthesis is primarily regulated by glucan synthase, however, it is unclear if the glucan synthase catalytic subunit gene (GluS) affects the growth and virulence of B. bassiana. In this study, we constructed the mutant of the B. bassiana glucan synthase catalytic subunit (ΔGluS) by homologous recombination and observed that glucan synthase knockout affects both spore germination and cell area. Further enzyme-based assays along with gene expression analysis of glucan synthase revealed a significant downregulation in the mutant strains compared to the wild type of B. bassiana. Moreover, the virulence of ΔGluS strains against gypsy moth (Lymantria dispar) showed no significant difference compared to the wild-type strains when injected, while the spraying gypsy moths with the conidia of ΔGluS was significantly more lethal than spraying the conidia of the wild type. Altogether, our study constructed a new, highly efficient B. bassiana mutant that can be used for pest control and provides a readily transferable method for other insect-entomopathogenic interaction studies., (Copyright © 2021 Elsevier Inc. All rights reserved.)

Functions of most Hsp70-coding genes remain unknown in filamentous fungi. Here, we show important roles of six Hsp70 homologs (Hsp70a-f) in Beauveria bassiana, a filamentous fungal insect pathogen that serves as a main source of wide-spectrum fungal insecticides. In phylogeny, Hsp70b-e, Hsp70g and Hsp70h are distinct from eight other partners that share the same clade with 14 Hsp70 proteins in model yeast. Among the 14 Hsp70-coding genes in B. bassiana, eight (hsp70g/hsp70h/ssa/ssb/ssc/kar/sse/ssz) were individually undeletable perhaps due to an essentiality of each for the fungal viability. Moderate defects in growth and conidiation occurred in the absence of hsp70e or hsp70f (lsh1). The disruption of hsp70f resulted in a reduction of 43% in conidial heat (45 °C) tolerance and of 97% in virulence, and the two reductions decreased to 19-27% and 18-45% in the disruption mutants of hsp70a to hsp70d respectively. Conidial UVB resistance decreased more in the absence of hsp70e (33%) than of hsp70f (25%), hsp70c (19%) or hsp70d (15%). All of these disruption mutants were differentially compromised in both cell wall integrity and antioxidant activity and also in cellular tolerance to Na + , Zn 2+ , Mn 2+ , Cu 2+ and/or Fe 2+ . Delayed acidification of submerged cultures and reduced secretion of organic acids occurred only in the absence of hsp70b or hsp70f. Our findings indicate that hsp70a-f are important for both host infection and multiple stress tolerance of B. bassiana, and functionally similar to or beyond the lsh1, ssb and ssz homologs characterized previously in some plant-pathogenic fungi., (Copyright © 2020 Elsevier Inc. All rights reserved.)

Modern genome analysis and phylogenomic methods have increased the number of fungal species, as well as enhanced appreciation of the degree of diversity within the fungal kingdom. In this context, we describe a new Parengyodontium species, P. americanum, which is phylogenetically related to the opportunistic human fungal pathogen P. album. Five unusual fungal isolates were recovered from five unique and confirmed coccidioidomycosis patients, and these isolates were subsequently submitted to detailed molecular and morphological identification procedures to determine identity. Molecular and morphological diagnostic analyses showed that the isolates belong to the Cordycipitaceae. Subsequently, three representative genomes were sequenced and annotated, and a new species, P. americanum, was identified. Using various genomic analyses, gene family expansions related to novel compounds and potential for ability to grow in diverse habitats are predicted. A general description of the genomic composition of this newly described species and comparison of genome content with Beauveria bassiana, Isaria fumosorosea and Cordyceps militaris shows a shared core genome of 6371 genes, and 148 genes that appear to be specific for P. americanum. This work provides the framework for future investigations of this interesting fungal species., (Copyright © 2020 Elsevier Inc. All rights reserved.)

Mitofilin acts as an essential organizer that maintains the complex architecture of the mitochondrial inner membrane (IM). In the present study, a yeast ortholog of mitofilin was characterized in the filamentous entomopathogenic fungus Beauveria bassiana; hence, it was named BbMtf. Mitochondrial localization was observed for B. bassiana mitofilin, and loss of this protein altered both the overall morphology and crista junction of the mitochondrial IM. Disruption of BbMtf resulted in reduced ATP synthesis and germination on the oligotrophic surface compared to the control. The ΔBbMtf mutant did not display significant variation in mycelial growth and stress tolerance. However, the BbMtf gene was required for conidiation and blastospore formation, and its absence led to a significant reduction in conidiation (40%) and blastospore yield (70%) in the mutant strain compared to the control. In addition, the development of the ΔBbMtf mutant in the host hemocoel was also significantly impaired, with a reduction of approximately 80% in spore concentration. Finally, disruption of BbMtf significantly attenuated fungal pathogenicity against insect hosts. Mitofilin, therefore, maintains the function of the mitochondrial IM, which contributes to the development and virulence of B. bassiana as a biocontrol fungus., (Copyright © 2019 Elsevier Inc. All rights reserved.)

VeA is a key velvet protein that regulates sexual/asexual development and secondary metabolism in filamentous fungi, particularly Aspergilli, but has not been explored yet in asexual insect mycopathogens, such as Beauveria bassiana. Here, we report a localization of B. bassiana VeA in the cytoplasm of hyphal cells exposed to either light or dark cue and its migration to the nucleus only in darkness. Deletion of veA resulted in facilitated hyphal growth and decreased cell length on rich media, light growth defects on scant media, and increased sensitivities to oxidation, high osmolarity and prolonged heat shock during colony growth. Compared to wild-type, the deletion mutant was much more triggered in conidiation at optimal 25 °C in darkness than in a light/dark (L:D) cycle of 12:12, indicating the role of VeA acting as a negative regulator of conidiation in a light-dependent manner. The mutant conidia produced at L:D 12:12 showed defects in germination, thermotolerance and UVB resistance but no change in virulence, contrasting to attenuated virulence for the mutant conidia produced in darkness. Intriguingly, fungal outgrowth and conidiation were markedly suppressed on the surfaces of the mutant-mummified insect cadavers, suggesting a significant role of VeA in fungal survival, dispersal and prevalence in host habitats. Transcriptomic analysis revealed 1248 and 1183 differentially expressed genes in the deletion mutant versus wild-type grown at L:D 0:24 and 12:12 respectively, including those involved in central developmental pathway and secondary metabolism. Altogether, VeA is functionally involved in asexual cycle, stress tolerance and transcriptional regulation of B. bassiana., (Copyright © 2019 Elsevier Inc. All rights reserved.)

Pbs2, Mkk1 and Ste7 orthologs are three mitogen-activated protein kinase (MAPK) kinases (MAPKKs) acting as checkpoints of the Hog1, Slt2 and Fus3 MAPK cascades that constitute major parts of fungal signaling network. Here, we show that three other MAPKK-like proteins (Mkk4/5/6) exist in Beauveria bassiana and other entomopathogenic or non-entomopathogenic fungi but lack in yeasts and aspergilli, and elucidate how they function in the fungal insect pathogen. Based on phenotypic defects of single-, double- and triple-deletion mutants, Mkk4, Mkk5 and Mkk6 played collaborative or independent roles in sustaining radial growth on various media, conidiation capacity, conidial germination, conidial UV-B resistance, and/or virulence. In stress assays, three single-deletion Δmkk mutants showed increased tolerance to cell wall stress but null response to a 3-h heat shock at 40 °C during normal incubation. Only did Δmkk6 exhibit increased sensitivity to either menadione or H 2 O 2 oxidation. Intriguingly, Δmkk5 and Δmkk6 displayed a remarkable increase in cellular sensitivity to a high osmolarity of NaCl or KCl instead of non-salt sorbitol, suggesting a link of their increased sensitivity to the toxicity of a high Na + /K + concentration rather than to the plausible osmotic stress of either salt. However, all of the deletion mutants showed no resistance to fludioxonil, a phenylpyrrole-type fungicide. A discussion is provided on whether Mkk4, Mkk5 and Mkk6 could be likely associated with or without the MAPK cascades in B. bassiana., (Copyright © 2018 Elsevier Inc. All rights reserved.)

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., (Copyright © 2018 Elsevier Inc. All rights reserved.)

Cyclophilin B (CypB) was previously revealed as one of many putative secretory proteins in the transcriptome of Beauveria bassiana infection to a lepidopteran pest. Here we show a main localization of CypB in hyphal cell walls and septa and its essential role in the in vitro and in vivo asexual cycles of the fungal insect pathogen. Deletion of cypB reduced colony growth by 16-42% on two rich media and 30 scant media with different carbon or nitrogen sources. The deletion mutant suffered a delayed conidiation on a standard medium and a final 47% reduction in conidial yield, accompanied with drastic transcript depression of several key genes required for conidiation and conidial maturation. The mutant conidia required 10h longer to germinate 50% at optimal 25°C than wild-type conidia. Intriguingly, cultivation of the mutant conidia in a trehalose-peptone broth mimic to insect hemolymph resulted in 83% reduction in blastospore yield but only slight decrease in biomass level, indicating severe defects in transition of hyphae to blastospores. LT 50 for the deletion mutant against Galleria mellonella larvae through normal cuticle infection was prolonged to 7.4d from a wild-type estimate of 4.7d. During colony growth, additionally, the deletion mutant displayed hypersensitivity to Congo red, menadione, H 2 O 2 and heat shock but increased tolerance to cyclosporine A and rapamycin. All of changes were restored by targeted gene complementation. Altogether, CypB takes part in sustaining normal growth, aerial conidiation, conidial germination, dimorphic transition, stress tolerance and pathogenicity in B. bassiana., (Copyright © 2017 Elsevier Inc. All rights reserved.)

The insect fungal pathogen Beauveria bassiana produces a number of distinct cell types that include aerial conidia, blastospores and haemolymph-derived cells, termed hyphal bodies, to adapt varied environment niches and within the host insect. These cells display distinct biochemical properties and surface structures, and a highly ordered outermost brush-like structure uniquely present on hyphal bodies, but not on any in vitro cells. Here, we found that the outermost structure on the hyphal bodies mainly consisted of proteins associated to structural wall components in that most of it could be removed by dithiothreitol (DTT) or proteinase K. DTT-treatment also caused delayed germination, decreased tolerance to ultraviolet irradiation and virulence of conidia or blastospores, with decreased adherence and alternated carbohydrate epitopes, suggesting involvement in fungal development, stress responses and virulence. To characterize these cell surface molecules, proteins were released from the living cells using DTT, and identified and quantitated using label-free quantitative mass spectrometry. Thereafter, a series of bioinformatics programs were used to predict cell surface-associated proteins (CSAPs), and 96, 166 and 54 CSAPs were predicted from the identified protein pools of conidia, blastospores and hyphal bodies, respectively, which were involved in utilization of carbohydrate, nitrogen, and lipid, detoxification, pathogen-host interaction, and likely other cellular processes. Thirteen, sixty-nine and six CSAPs were exclusive in conidia, blastospores and hyphal bodies, respectively, which were verified by eGFP-tagged proteins at their N-terminus. Our data provide a crucial cue to understand mechanism of B. bassiana to adapt to varied environment and interaction with insect host., (Copyright © 2016 Elsevier Inc. All rights reserved.)

Vacuolar ATPase (V-ATPase) is a conserved multi-subunit protein complex that mediates intracellular acidification in fungi. Here we show functional diversity of V-ATPase subunit H (BbVmaH) in Beauveria bassiana, a filamentous fungal insect pathogen. Deletion of BbvmaH resulted in elevated vacuolar pH, increased Ca 2+ level in cytosol but not in vacuoles, accelerated culture acidification and reduced accumulation of extracellular ammonia. Aerial conidiation and submerged blastospore production were largely delayed and reduced in the deletion mutant, respectively, accompanied with a significant delay in conidial germination, alterations of conidia and blastospores in morphology, size and/or density, and severe growth defects in minimal media with different carbon and nitrogen sources. Despite null responses to osmotic, oxidative and cell wall perturbing stresses, the deletion mutant showed increased sensitivity to Ca 2+ , Zn 2+ and Cu 2+ during growth while its conidia were less tolerant to a wet-heat stress at 45°C and UV-B irradiation. Intracellular glycerol and mannitol contents also decreased significantly. Its virulence to Galleria mellonella larvae was significantly attenuated when conidia were topically applied for normal cuticle infection or injected into haemocoel for cuticle-bypassing infection. All phenotypic changes were restored by targeted gene complementation. Our results indicate that BbVmaH plays an important role in sustaining not only vacuolar acidification but also cytosolic calcium accumulation, ambient pH homeostasis, in vitro asexual cycle and virulence in B. bassiana., (Copyright © 2016 Elsevier Inc. All rights reserved.)

Miro homologues are small mitochondrial Rho GTPases belonging to the Ras superfamily across organisms and are generally unexplored in filamentous fungi. Here we identified a Miro orthologue (bMiro) in Beauveria bassiana, a filamentous fungal insect pathogen as a classic biological control agent of insect pests. This orthologue was proven to anchor on mitochondrial outer membrane in a manner depending completely upon a short C-terminal transmembrane domain. As a result of bmiro deletion, mitochondria in hyphal cells were largely aggregated, and their mass and mobility were reduced, accompanied with a remarkable decrease in ATP content but little change in mitochondrial morphology. The deletion mutant became 42%, 37%, 19% and 10% more tolerant to Ca(2+), Mn(2+), Zn(2+) and Mg(2+) than wild-type, respectively, during cultivation in a minimal medium under normal conditions. The deletion mutant also showed mild defects in conidial germination, vegetative growth, thermotolerance, UV-B resistance and virulence despite null response to oxidative and osmotic stresses. All these phenotypic changes were restored by targeted gene complementation. Our results indicate that bMiro can control mitochondrial distribution and movement required for the transport of ATP-form energy and metal ions and contributes significantly to the fungal potential against insect pests through the control., (Copyright © 2016 Elsevier Inc. All rights reserved.)

The entomopathogenic fungus, Beauveria bassiana, is of environmental and economic importance as an insect pathogen, currently used for the biological control of a number of pests. Cell wall integrity and conidiation are critical parameters for the ability of the fungus to infect insects and for production of the infectious propagules. The contribution of calcineurin and the Slt2 MAP kinase to cell wall integrity and development in B. bassiana was investigated. Gene knockouts of either the calcineurin CNA1 subunit or the Slt2 MAP kinase resulted in decreased tolerance to calcofluor white and high temperature. In contrast, the Δcna1 strain was more tolerant to Congo red but more sensitive to osmotic stress (NaCl, sorbitol) than the wild type, whereas the Δslt2 strain had the opposite phenotype. Changes in cell wall structure and composition were seen in the Δslt2 and Δcna1 strains during growth under cell wall stress as compared to the wild type. Both Δslt2 and Δcna1 strains showed significant alterations in growth, conidiation, and viability. Elevation of intracellular ROS levels, and decreased conidial hydrophobicity and adhesion to hydrophobic surfaces, were also seen for both mutants, as well as decreased virulence. Under cell wall stress conditions, inactivation of Slt2 significantly repressed CN-mediated phosphatase activity suggesting some level of cross talk between the two pathways. Comparative transcriptome profiling of the Δslt2 and Δcna1 strains revealed alterations in the expression of distinct gene sets, with overlap in transcripts involved in cell wall integrity, stress response, conidiation and virulence. These data illustrate convergent and divergent phenotypes and targets of the calcineurin and Slt2 pathways in B. bassiana., (Copyright © 2015 Elsevier Inc. All rights reserved.)

Two Ras ATPases (Ras1 and Ras2) are well known to regulate antagonistically or cooperatively various cellular events in many fungi. Here we show the significance of a novel Ras homolog (Ras3) for Beauveria bassiana. Ras3 possesses five domains and two GTP/GDP switches typical for Ras family and was proven to localize to plasma membrane despite the position change of a membrane-targeting cysteine in C-terminal CAAX motif. Deletion of ras3 altered temporal transcription pattern of ras1 instead of ras2. Compared with wild-type, Δras3 grew significantly faster in a rich medium but slower in some minimal media, and produced far fewer conidia with impaired quality, which was evident with slower germination, attenuated virulence, reduced thermotolerance and decreased UV-B resistance. Moreover, Δras3 was much more sensitive to the oxidative stress of menadione than of H2O2 and to the stress of high osmolarity than of cell wall perturbation during growth. The high sensitivity of Δras3 to menadione was concurrent with reductions in both gene transcripts and total activity of superoxide dismutases. Intriguingly, the high osmosensitivity was concurrent with not only reduced transcripts of a critical transcription factor (Msn2) and most signaling proteins in the high-osmolarity-glycerol pathway of Δras3 but nearly undetectable phosphorylation signal of Hog1 hallmarking the pathway. All the changes were restored by ras3 complementation. Taken together, Ras3 is involved in the Hog1 pathway required for osmoregulation and hence can positively regulate conidiation, germination, multi-stress tolerance and virulence linked to the biological control potential of the filamentous insect pathogen., (Copyright © 2015 Elsevier Inc. All rights reserved.)

Multiple Vcx1 (vacuolar calcium exchanger) paralogues exist in many filamentous fungi but are functionally unexplored unlike a single Vcx1 ortholog well characterized in yeasts. Here we show that five Vcx1 paralogues (Vcx1A-E) in Beauveria bassiana are conditionally functional for intracellular Ca(2+) homeostasis and contribute differentially to multistress tolerance and virulence in the filamentous entomopathogen. Each vcx1 deletion drastically upregulated transcriptional expressions of four other partners and six P-type Ca(2+)-ATPases, resulting in elevated or lowered intracellular Ca(2+) concentration in some deletion mutants treated with Ca(2+) stress or untreated at 25 and 30 °C. When calcineurin was inactivated by cyclosporine A, Ca(2+) tolerance decreased by 11-17% in five Δvcx1 mutants, but Mn(2+) sensitivity increased only in Δvcx1A and Δvcx1D, at optimal 25 °C. These two mutants were also more sensitive to Ca(2+) stress at 30 °C when calcineurin was active, and showed minor growth defect at 25 and 30 °C when calcineurin was inactive. Moreover, all the Δvcx1 mutants were more sensitive to dithiothreitol (stress-response trigger to endoplasmic reticulum) and Congo red (cell wall stressor); three of them were consistently less tolerant to the oxidants menadione and H2O2. The fungal virulence to Galleria mellonella larvae decreased by 15-40% in four Δvcx1 mutants excluding Δvcx1E, which was uniquely defective in conidial thermotolerance. All the changes were restored by each vcx1 complementation. Our findings indicate that the five Vcx1 paralogues in B. bassiana contribute differentially to calcineurin-dependent Ca(2+)/Mn(2+) tolerance, multistress responses and virulence, and recall attention to multifunctional Vcx1 paralogues in filamentous fungi., (Copyright © 2014 Elsevier Inc. All rights reserved.)

Members of α-1,2-mannosyltransferase (Ktr) family are required for protein O-mannosylation for the elongation of Ser/Thr mannose residues in yeasts but functionally unknown in most filamentous fungi. Here we characterized the functions of the Ktr orthologues Ktr1, Ktr4 and Kre2/Mnt1 in Beauveria bassiana, a filamentous enotmopathogen, and found that they were positive, but differential, mediators of many biological traits. Inactivation of Ktr4 and Kre2 resulted in 92% reduction of conidial yield on a standard medium and growth defects on substrates with altered carbon or nitrogen sources and availability, accompanied with reduced conidial size and complexity. This contrasts to the dispensability of Ktr1 for fungal growth and conidiation. More cell wall damage occurred in Δktr4 and Δkre2 than in Δktr1, including altered contents of the cell wall components mannoproteins, α-glucans and chitin, more carbohydrate epitopes changed on conidial surfaces, much lower conidial hydrophobicity, and thinner cell walls. Consequently, Δktr4 and Δkre2 became more sensitive to oxidation and cell wall perturbation than Δktr1 during colony growth or conidial germination despite less difference in their sensitivities to two osmotic agents. Conidial thermotolerance, UV-B resistance and virulence were all lowered greatly in Δktr4 and Δkre2 but only the thermotolerance decreased in Δktr1. All the phenotypical changes were well restored to wild-type levels by the complementation of each target gene. Our results indicate that Ktr4 and Kre2 contribute more to the biocontrol potential of B. bassiana than Ktr1 although all of them are significant contributors., (Copyright © 2014 Elsevier Inc. All rights reserved.)

Msn2/4 transcription factors in some fungi have null effects on virulence and cellular stress responses. Here we found that the transcriptional regulation of Msn2 orthologs is vital for the conidiation, virulence and multi-stress responses of Beauveria bassiana (Bb) and Metarhizium robertsii (Mr), which lack Msn4 orthologs. Compared to wild-type and complemented strains of each fungus with all similar phenotypes, ΔBbmsn2 and ΔMrmsn2 showed remarkable defects in conidial yield (∼40% decrease) and virulence (∼25% decrease). Both delta mutants lost 20-65% of their tolerances to hyperosmolarity, oxidation, carbendazim, cell wall perturbing and high temperature at 34 °C during colony growth. Their conidia were also significantly (18-41%) less tolerant to oxidation, hyperosmolarity, wet-heat stress at 45 °C and UV-B irradiation. Accompanied with the defective phenotypes, several conidiation- and virulence-associated genes were greatly repressed in ΔBbmsn2 and ΔMrmsn2. Moreover, differentially expressed genes in the transcriptomes of ΔBbmsn2 versus wild type were ∼3% more under oxidative stress, but ∼12% fewer under heat shock, than those in the ΔMrmsn2 counterparts. Many stress-responsive effector genes and cellular signaling factors were remarkably downregulated. Taken together, the two entomopathogens could have evolved somewhat distinct stress-responsive mechanisms finely tuned by Msn2, highlighting the biological significance of Msn2 orthologs for filamentous fungi., (Copyright © 2013 Elsevier Inc. All rights reserved.)

Entomopathogenic fungi, such as Beauveria bassiana, are key environmental pathogens of insects that have been exploited for biological control of insect pests. Mitogen-activated protein (MAP) kinases play crucial roles in regulating fungal development, growth, and pathogenicity, mediating responses to the environment. Bbslt2, encoding for an Slt2 family MAPK, was isolated and characterized from B. bassiana. Gene disruption of Bbslt2 affected growth, caused a significant reduction in conidial production and viability, and increased sensitivity to Congo Red and fungal cell wall degrading enzymes. ΔBbslt2 mutants were altered in cell wall structure and composition, which included temperature dependent chitin accumulation, reductions in conidial and hyphal hydrophobicity, and alterations in cell surface carbohydrate epitopes. The ΔBbslt2 strain also showed hypersensitivity to heat shock and altered trehalose accumulation, which could only be partially attributed to changes in the expression of trehalase (ntl1). Insect bioassays revealed decreased virulence in the ΔBbslt2 strain using both topical and intrahemoceol injection assays. These results indicate that Bbslt2 plays an important role in conidiation, viability, cell wall integrity and virulence in B. bassiana. Our findings are discussed within the context of the two previous MAP kinases characterized from B. bassiana., (Copyright © 2012 Elsevier Inc. All rights reserved.)

The entomopathogen Beauveria bassiana has an extremely diverse insect host range in addition to a saprophytic phase. The molecular basis for this plasticity was investigated by a comparative analysis of gene expression patterns through cDNA-AFLPs of a B. bassiana isolate grown on cuticular extracts of insects of diverse orders as well as synthetic medium. For some of the fragments, expression patterns were verified by Q-RT-PCR. Among the differentially expressed genes two proteases were identified, which are known to be directly involved in the process of pathogenesis in entomopathogenic fungi. However, the majority of the transcript derived fragments identified have a rather indirect function in fungal pathogenesis, as they are involved in the regulation of gene expression, signal transduction, cytoskeleton formation or secretion. In general, the gene expression profile of the fungal isolate on cuticular extracts of diverse insects was pretty similar. This sheds light on the putative generalist nature of B. bassiana with its ability to penetrate many different insect cuticles possibly due to a rather stereotype gene expression program.