Impaired ribosome biogenesis disrupts the integration between morphogenesis and nuclear duplication during the germination of Aspergillus fumigatus

2-Nonanol produced by Bacillus velezensis EM-1: a new biocontrol agent against tobacco brown spot

Tobacco brown spot disease, caused by Alternaria alternata, poses a significant threat to crop production. Traditional control methods, particularly chemical fungicides, have raised concerns about environmental impact and resistance. Although our previous research has shown that volatile compounds produced by Bacillus velezensis EM-1 can effectively suppress A. alternata, the specific antifungal compounds and their mechanisms remain unclear. In this study, exposure to the volatiles from strain EM-1 significantly inhibited the mycelial growth and spore germination of A. alternata, with 2-nonanol identified as the most potent antifungal compound. Fumigation experiments revealed that 2-nonanol exhibited strong dose-dependent toxicity, with an EC50 of 0.1055 μL/cm3 and a minimum inhibitory concentration of 0.2166 μL/cm3. In vivo experiments on tobacco leaves confirmed that 2-nonanol effectively reduced tobacco brown spot disease incidence and slowed lesion expansion. Transcriptome analysis indicated that 2-nonanol downregulated the expression of genes encoding D-glucose synthesis in carbon metabolism, which limited energy acquisition by A. alternata. Moreover, the expression of antioxidant enzymes, including superoxide dismutase (SOD) and catalase (CAT), was markedly suppressed by 2-nonanol, thereby exacerbating cellular damage induced by oxidative stress. These findings suggest that 2-nonanol holds potential as a biocontrol agent for managing tobacco brown spot disease, underscoring the promising role of volatile organic compounds (VOCs) in the development of environmentally friendly biocontrol products.

A Nucleolar Protein, MoRRP8 Is Required for Development and Pathogenicity in the Rice Blast Fungus

The nucleolus is the largest, membrane-less organelle within the nucleus of eukaryotic cell that plays a critical role in rRNA transcription and assembly of ribosomes. Recently, the nucleolus has been shown to be implicated in an array of processes including the formation of signal recognition particles and response to cellular stress. Such diverse functions of nucleolus are mediated by nucleolar proteins. In this study, we characterized a gene coding a putative protein containing a nucleolar localization sequence (NoLS) in the rice blast fungus, Magnaporthe oryzae. Phylogenetic and domain analysis suggested that the protein is orthologous to Rrp8 in Saccharomyces cerevisiae. MoRRP8-GFP (translational fusion of MoRRP8 with green fluorescence protein) co-localizes with a nucleolar marker protein, MoNOP1 fused to red fluorescence protein (RFP), indicating that MoRRP8 is a nucleolar protein. Deletion of the MoRRP8 gene caused a reduction in vegetative growth and impinged largely on asexual sporulation. Although the asexual spores of ΔMorrp8 were morphologically indistinguishable from those of wild-type, they showed delay in germination and reduction in appressorium formation. Our pathogenicity assay revealed that the MoRRP8 is required for full virulence and growth within host plants. Taken together, these results suggest that nucleolar processes mediated by MoRRP8 is pivotal for fungal development and pathogenesis.

Effect of Water Activity on Conidia Germination in Aspergillus flavus

In this study, we explored the mechanism underlying Aspergillus flavus conidia germination inhibited by decreased water activity. The impact of low water activity was analyzed at 4 h, 8 h and 12 h. Additionally, we demonstrated that low water activity affected cell shape and decreased cell sizes. Transcriptomics found numerous differentially expressed genes (DEGs) during the first 12 h of germination, with 654 DEGs observed among 4 h, 8 h and 12 h. In particular, more DEGs were detected at 8 h of germinating. Therefore, proteomics was performed at 8 h, and 209 differentially expressed proteins (DEPs) were speculated, with 94 up-regulated and 115 down-regulated. Combined analysis of KEGG of transcriptomics and proteomics demonstrated that the dominant pathways were nutrient metabolism and translation. We also found several DEGs and DEPs in the Mitogen Activated Protein Kinase (MAPK) pathway. Therefore, we concluded that low water activity inhibited conidia germination, causing unregular morphology. In addition, low water activity influenced expression of creA, TreB in carbohydrate metabolism, Clr4, RmtA in amino acid metabolism and RPL37, RPL3 in translation in Aspergillus flavus.

The pathogenicity ofAspergillus fumigatus, drug resistance, and nanoparticle delivery

The genus Aspergillus includes fungal species that cause major health issues of significant economic importance. These microorganisms are also the culprit for production of carcinogenic aflatoxins in grain storages, contaminating crops, and economically straining the production process. Aspergillus fumigatus is a very important pathogenic species, being responsible for high human morbidity and mortality on a global basis. The prevalence of these infections in immunosuppressed individuals is on the rise, and physicians struggle with the diagnosis of these deadly pathogens. Several virulence determinants facilitate fungal invasion and evasion of the host immune response. Metabolic functions are also important for virulence and drug resistance, since they allow fungi to obtain nutrients for their own survival and growth. Following a positive diagnostic identification, mortality rates remain high due, in part, to emerging resistance to frequently used antifungal drugs. In this review, we discuss the role of the main virulence, drug target, and drug resistance determinants. We conclude with the review of new technologies being developed to treat aspergillosis. In particular, microsphere and nanoparticle delivery systems are discussed in the context of improving drug bioavailability. Aspergillus will likely continue to cause problematic infections in immunocompromised patients, so it is imperative to improve treatment options.

Polysome profiling reveals broad translatome remodeling during endoplasmic reticulum (ER) stress in the pathogenic fungus Aspergillus fumigatus

BACKGROUND

The unfolded protein response (UPR) is a network of intracellular signaling pathways that supports the ability of the secretory pathway to maintain a balance between the load of proteins entering the endoplasmic reticulum (ER) and the protein folding capacity of the ER lumen. Current evidence indicates that several pathogenic fungi rely heavily on this pathway for virulence, but there is limited understanding of the mechanisms involved. The best known functional output of the UPR is transcriptional upregulation of mRNAs involved in ER homeostasis. However, this does not take into account mechanisms of translational regulation that involve differential loading of ribosomes onto mRNAs. In this study, a global analysis of transcript-specific translational regulation was performed in the pathogenic mold Aspergillus fumigatus to determine the nature and scope of the translational response to ER stress.

RESULTS

ER stress was induced by treating the fungus with dithiothreitol, tunicamycin, or a thermal up-shift. The mRNAs were then fractionated on the basis of ribosome occupancy into an under-translated pool (U) and a well-translated pool (W). The mRNAs were used to interrogate microarrays and the ratio of the hybridization signal (W/U) was used as an indicator of the relative translational efficiency of a mRNA under each condition. The largest category of translationally upregulated mRNAs during ER stress encoded proteins involved in translation. Components of the ergosterol and GPI anchor biosynthetic pathways also showed increased polysome association, suggesting an important role for translational regulation in membrane and cell wall homeostasis. ER stress induced limited remodeling of the secretory pathway translatome. However, a select group of transcription factors was translationally upregulated, providing a link to subsequent modification of the transcriptome. Finally, we provide evidence that one component of the ER stress translatome is a novel mRNA isoform from the yvc1 gene that is induced by ER stress in a UPR-dependent manner.

CONCLUSIONS

Together, these findings define a core set of mRNAs subject to translational control during the adaptive response to acute ER stress in A. fumigatus and reveal a remarkable breadth of functions that are needed to resolve ER stress in this organism.

Uncovering cellular circuitry controlling temperature-dependent fungal morphogenesis

Temperature change is a ubiquitous environmental signal, which exerts powerful control over the development and virulence of microbial pathogens. For Candida albicans, the leading fungal pathogen of humans, temperature influences mating, phenotypic switching, resistance to antifungal drugs and the morphogenetic transition from yeast to filamentous growth. C. albicans morphogenesis is profoundly influenced by temperature, and most filament-inducing cues depend on a concurrent increase in temperature to 37°C before morphogenesis can occur, although the molecular mechanisms underpinning this temperature-dependent developmental transition remain largely unknown. We established that the thermally responsive molecular chaperone Hsp90 orchestrates temperature-dependent morphogenesis, via previously uncharacterized cellular circuitry, comprised of the cyclin-dependent kinase Pho85, the cyclin Pcl1 and the transcriptional regulator Hms1. Here we elaborate on Hsp90's pleiotropic effects on temperature-dependent morphogenetic circuitry, and highlight how changes in protein form and function in response to stress complements the diverse repertoire of mechanisms of microbial temperature sensing.

Regulatory circuitry governing fungal development, drug resistance, and disease

Pathogenic fungi have become a leading cause of human mortality due to the increasing frequency of fungal infections in immunocompromised populations and the limited armamentarium of clinically useful antifungal drugs. Candida albicans, Cryptococcus neoformans, and Aspergillus fumigatus are the leading causes of opportunistic fungal infections. In these diverse pathogenic fungi, complex signal transduction cascades are critical for sensing environmental changes and mediating appropriate cellular responses. For C. albicans, several environmental cues regulate a morphogenetic switch from yeast to filamentous growth, a reversible transition important for virulence. Many of the signaling cascades regulating morphogenesis are also required for cells to adapt and survive the cellular stresses imposed by antifungal drugs. Many of these signaling networks are conserved in C. neoformans and A. fumigatus, which undergo distinct morphogenetic programs during specific phases of their life cycles. Furthermore, the key mechanisms of fungal drug resistance, including alterations of the drug target, overexpression of drug efflux transporters, and alteration of cellular stress responses, are conserved between these species. This review focuses on the circuitry regulating fungal morphogenesis and drug resistance and the impact of these pathways on virulence. Although the three human-pathogenic fungi highlighted in this review are those most frequently encountered in the clinic, they represent a minute fraction of fungal diversity. Exploration of the conservation and divergence of core signal transduction pathways across C. albicans, C. neoformans, and A. fumigatus provides a foundation for the study of a broader diversity of pathogenic fungi and a platform for the development of new therapeutic strategies for fungal disease.

Aspergillus fumigatus: virulence genes in a street-smart mold

Infections with the filamentous fungus Aspergillus fumigatus are among the most devastating of the systemic mycoses. Unlike most primary pathogens, which possess virulence traits that developed in association with a host organism, evidence suggests that the virulence of A. fumigatus entails a collection of 'street-smart' attributes that have evolved to resist the adverse selection pressures encountered in decaying vegetation. These features enhance the overall competitiveness of the organism in its environmental niche but are also thought to promote growth and survival in a human host. Although many of the genes that are responsible for these characteristics do not fit into the classical definition of a virulence factor, they are nonetheless important to the pathogenesis of aspergillosis and may therefore provide novel opportunities for antifungal development.