The Extracellular Superoxide Dismutase Sod5 From Fusarium oxysporum Is Localized in Response to External Stimuli and Contributes to Fungal Pathogenicity

Exploring Paenibacillus terrae B6a as a sustainable biocontrol agent for Fusarium proliferatum

The reliance on chemical fungicides for crop protection has raised environmental and health concerns, prompting the need for sustainable and eco-friendly alternatives. Biological control, using antagonistic microorganisms like Paenibacillus terrae B6a, offers an eco-friendly approach to managing disease causing phytopathogens. The objective of the study was to assess the efficacy of P. terrae B6a as a biocontrol agent against Fusarium proliferatum PPRI 31301, focusing on its in vitro antagonistic activity, its impact on fungal morphology and enzymatic content, and its ability to mitigate pathogen-induced stress in maize plants. In vitro antagonistic activity of B6a against F. proliferatum was carried out using standard protocol. In planta assay was carried out by bio-priming of maize seeds with 1 × 106 CFU/mL of B6a and infected with F. proliferatum for 7 days. Biochemical, enzymatic and antioxidants activities of bio-primed maize roots under F. proliferatum infection was carried out using spectrophotometric methods. In vitro antagonistic assays using dual culture and intracellular crude metabolites inhibited 70.15 and 71.64%, respectively, of F. proliferatum. Furthermore, B6a altered the morphology and mycelia structure of F. proliferatum under High resolution scanning electron microscopy (HR-SEM). This was supported by an increase (p < 0.05) in the chitin contents (48.03%) and a decrease (p < 0.05) in the extracellular polysaccharide content (48.99%) and endo-β-1,4-glucanase activity (42.32%). The infection of maize seeds with F. proliferatum resulted in a significant decrease (p < 0.05) in root lengths (37%). Relative to the control and the infected seeds, bio-priming with B6a shows a significant increase (p < 0.05) in the root lengths (44.99%), with a significant decrease (p < 0.05) in reactive oxygen species (ROS)-induced oxidative damage. In conclusion, P. terrae B6a may be a good biocontrol candidate and may be formulated into a bio-fungicide to control F. proliferatum and other related phytopathogens in economically important crops.

Antioxidant Systems of Plant Pathogenic Fungi: Functions in Oxidative Stress Response and Their Regulatory Mechanisms

During the infection process, plant pathogenic fungi encounter plant-derived oxidative stress, and an appropriate response to this stress is crucial to their survival and establishment of the disease. Plant pathogenic fungi have evolved several mechanisms to eliminate oxidants from the external environment and maintain cellular redox homeostasis. When oxidative stress is perceived, various signaling transduction pathways are triggered and activate the downstream genes responsible for the oxidative stress response. Despite extensive research on antioxidant systems and their regulatory mechanisms in plant pathogenic fungi, the specific functions of individual antioxidants and their impacts on pathogenicity have not recently been systematically summarized. Therefore, our objective is to consolidate previous research on the antioxidant systems of plant pathogenic fungi. In this review, we explore the plant immune responses during fungal infection, with a focus on the generation and function of reactive oxygen species. Furthermore, we delve into the three antioxidant systems, summarizing their functions and regulatory mechanisms involved in oxidative stress response. This comprehensive review provides an integrated overview of the antioxidant mechanisms within plant pathogenic fungi, revealing how the oxidative stress response contributes to their pathogenicity.

Innexin hemichannel activation by Microplitis bicoloratus ecSOD monopolymer reduces ROS

The extracellular superoxide dismutases (ecSODs) secreted by Microplitis bicoloratus reduce the reactive oxygen species (ROS) stimulated by the Microplitis bicoloratus bracovirus. Here, we demonstrate that the bacterial transferase hexapeptide (hexapep) motif and bacterial-immunoglobulin-like (BIg-like) domain of ecSODs bind to the cell membrane and transiently open hemichannels, facilitating ROS reductions. RNAi-mediated ecSOD silencing in vivo elevated ROS in host hemocytes, impairing parasitoid larva development. In vitro, the ecSOD-monopolymer needed to be membrane bound to open hemichannels. Furthermore, the hexapep motif in the beta-sandwich of ecSOD49 and ecSOD58, and BIg-like domain in the signal peptides of ecSOD67 were required for cell membrane binding. Hexapep motif and BIg-like domain deletions induced ecSODs loss of adhesion and ROS reduction failure. The hexapep motif and BIg-like domain mediated ecSOD binding via upregulating innexins and stabilizing the opened hemichannels. Our findings reveal a mechanism through which ecSOD reduces ROS, which may aid in developing anti-redox therapy.

Sulfur metabolism-mediated fungal glutathione biosynthesis is essential for oxidative stress resistance and pathogenicity in the plant pathogenic fungus Fusarium graminearum

IMPORTANCE

Fusarium graminearum is a destructive fungal pathogen that causes Fusarium head blight (FHB) on a wide range of cereal crops. To control fungal diseases, it is essential to comprehend the pathogenic mechanisms that enable fungi to overcome host defenses during infection. Pathogens require an oxidative stress response to overcome host-derived oxidative stress. Here, we identify the underlying mechanisms of the Fgbzip007-mediated oxidative stress response in F. graminearum. ChIP-seq and subsequent genetic analyses revealed that the role of glutathione in pathogenesis is not dependent on antioxidant functions in F. graminearum. Altogether, this study establishes a comprehensive framework for the Fgbzip007 regulon on pathogenicity and oxidative stress responses, offering a new perspective on the role of glutathione in pathogenicity.

Elucidating the Obligate Nature and Biological Capacity of an Invasive Fungal Corn Pathogen

Tar spot is a devasting corn disease caused by the obligate fungal pathogen Phyllachora maydis. Since its initial identification in the United States in 2015, P. maydis has become an increasing threat to corn production. Despite this, P. maydis has remained largely understudied at the molecular level, due to difficulties surrounding its obligate lifestyle. Here, we generated a significantly improved P. maydis nuclear and mitochondrial genome, using a combination of long- and short-read technologies, and also provide the first transcriptomic analysis of primary tar spot lesions. Our results show that P. maydis is deficient in inorganic nitrogen utilization, is likely heterothallic, and encodes for significantly more protein-coding genes, including secreted enzymes and effectors, than previous determined. Furthermore, our expression analysis suggests that, following primary tar spot lesion formation, P. maydis might reroute carbon flux away from DNA replication and cell division pathways and towards pathways previously implicated in having significant roles in pathogenicity, such as autophagy and secretion. Together, our results identified several highly expressed unique secreted factors that likely contribute to host recognition and subsequent infection, greatly increasing our knowledge of the biological capacity of P. maydis, which have much broader implications for mitigating tar spot of corn. [Formula: see text] Copyright © 2023 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Conservation and Expansion of Transcriptional Factor Repertoire in the Fusarium oxysporum Species Complex

The Fusarium oxysporum species complex (FOSC) includes both plant and human pathogens that cause devastating plant vascular wilt diseases and threaten public health. Each F. oxysporum genome comprises core chromosomes (CCs) for housekeeping functions and accessory chromosomes (ACs) that contribute to host-specific adaptation. This study inspects global transcription factor profiles (TFomes) and their potential roles in coordinating CC and AC functions to accomplish host-specific interactions. Remarkably, we found a clear positive correlation between the sizes of TFomes and the proteomes of an organism. With the acquisition of ACs, the FOSC TFomes were larger than the other fungal genomes included in this study. Among a total of 48 classified TF families, 14 families involved in transcription/translation regulations and cell cycle controls were highly conserved. Among the 30 FOSC expanded families, Zn2-C6 and Znf_C2H2 were most significantly expanded to 671 and 167 genes per family including well-characterized homologs of Ftf1 (Zn2-C6) and PacC (Znf_C2H2) that are involved in host-specific interactions. Manual curation of characterized TFs increased the TFome repertoires by 3% including a disordered protein Ren1. RNA-Seq revealed a steady pattern of expression for conserved TF families and specific activation for AC TFs. Functional characterization of these TFs could enhance our understanding of transcriptional regulation involved in FOSC cross-kingdom interactions, disentangle species-specific adaptation, and identify targets to combat diverse diseases caused by this group of fungal pathogens.

Conservation and Expansion of Transcriptional Factor Repertoire in the Fusarium oxysporum Species Complex

The Fusarium oxysporum species complex (FOSC) includes both plant and human pathogens that cause devastating plant vascular wilt diseases and threaten public health. Each F. oxysporum genome comprises core chromosomes (CCs) for housekeeping functions and accessory chromosomes (ACs) that contribute to host-specific adaptation. This study inspected global transcription factor profiles (TFomes) and their potential roles in coordinating CCs and ACs functions to accomplish host-specific pathogenicity. Remarkably, we found a clear positive correlation between the sizes of TFome and proteome of an organism, and FOSC TFomes are larger due to the acquisition of ACs. Among a total of 48 classified TF families, 14 families involved in transcription/translation regulations and cell cycle controls are highly conserved. Among 30 FOSC expanded families, Zn2-C6 and Znf_C2H2 are most significantly expanded to 671 and 167 genes per family, including well-characterized homologs of Ftf1 (Zn2-C6) and PacC (Znf_C2H2) involved in host-specific interactions. Manual curation of characterized TFs increased the TFome repertoires by 3%, including a disordered protein Ren1. Expression profiles revealed a steady expression of conserved TF families and specific activation of AC TFs. Functional characterization of these TFs could enhance our understanding of transcriptional regulation involved in FOSC cross-kingdom interactions, disentangle species-specific adaptation, and identify targets to combat diverse diseases caused by this group of fungal pathogens.

Metabolomic and Transcriptome Analysis of the Inhibitory Effects of Bacillus subtilis Strain Z-14 against Fusarium oxysporum Causing Vascular Wilt Diseases in Cucumber

Controlling cucumber Fusarium wilt caused by Fusarium oxysporum f. sp. cucumerinum (FOC) with Bacillus strains is a hot research topic. However, the molecular mechanism of Bacillus underlying the biocontrol of cucumber wilt is rarely reported. In this study, B. subtilis strain Z-14 showed significant antagonistic activity against FOC, and the control effect reached 88.46% via pot experiment. Microscopic observations showed that strain Z-14 induced the expansion and breakage of FOC hyphae. The cell wall thickness was uneven, and the organelle structure was degraded. The combined analysis of metabolome and transcriptome showed that strain Z-14 inhibited the FOC infection by inhibiting the synthesis of cell wall and cell membrane, energy metabolism, and amino acid synthesis of FOC mycelium, inhibiting the clearance of reactive oxygen species (ROS) and the secretion of cell wall-degrading enzymes (CWDEs), thereby affecting mitogen-activated protein kinase (MAPK) signal transduction and inhibiting the transport function.

Characterization of ancestral Fe/Mn superoxide dismutases indicates their cambialistic origin

Superoxide dismutases (SODs) are critical metalloenzymes mitigating the damages of the modern oxygenated world. However, the emergence of one family of SODs, the Fe/Mn SOD, has been recurrently proposed to predate the great oxygenation event (GOE). This ancient family lacks metal binding selectivity, but displays strong catalytic selectivity. Therefore, some homologues would only be active when bound to Fe or Mn, although others, dubbed cambialistic, would function when loaded with either ion. This posed the longstanding question about the identity of the cognate metal ion of the first SODs to emerge. In this work, we utilize ancestral sequence reconstruction techniques to infer the earliest SODs. We show that the "ancestors" are active in vivo and in vitro. Further, we test their metal specificity and demonstrate that they are cambialistic in nature. Our findings shed light on how the predicted Last Common Universal Ancestor was capable of dealing with decomposition of the superoxide anion, and the early relationship between life, oxygen, and metal ion availability.

Biochemical Analysis of CaurSOD4, a Potential Therapeutic Target for the Emerging Fungal Pathogen Candida auris

Candida auris is an emerging multidrug-resistant fungal pathogen. With high mortality rates, there is an urgent need for new antifungals to combat C. auris. Possible antifungal targets include Cu-only superoxide dismutases (SODs), extracellular SODs that are unique to fungi and effectively combat the superoxide burst of host immunity. Cu-only SODs are essential for the virulence of diverse fungal pathogens; however, little is understood about these enzymes in C. auris. We show here that C. auris secretes an enzymatically active Cu-only SOD (CaurSOD4) when cells are starved for Fe, a condition mimicking host environments. Although predicted to attach to cell walls, CaurSOD4 is detected as a soluble extracellular enzyme and can act at a distance to remove superoxide. CaurSOD4 selectively binds Cu and not Zn, and Cu binding is labile compared to bimetallic Cu/Zn SODs. Moreover, CaurSOD4 is susceptible to inhibition by various metal-binding drugs that are without effect on mammalian Cu/Zn SODs. Our studies highlight CaurSOD4 as a potential antifungal target worthy of consideration.

The Glycosylphosphatidylinositol-Anchored Superoxide Dismutase of Scedosporium apiospermum Protects the Conidia from Oxidative Stress

Scedosporium species are common fungal pathogens in patients with cystic fibrosis (CF). To colonize the CF lungs, fungi must cope with the host immune response, especially the reactive oxygen species (ROS) released by phagocytic cells. To this aim, pathogens have developed various antioxidant systems, including superoxide dismutases (SODs) which constitute the first-line protection against oxidative stress. Interestingly, one of the S. apiospermum SOD-encoding genes (SODD gene) exhibits a glycosylphosphatidylinositol (GPI) anchor-binding site and encodes a conidial-specific surface SOD. In this study, a SODDΔ mutant was engineered from a non-homologous end joining-deficient strain (KU70Δ) of S. apiospermum. Compared to its parent strain, the double mutant KU70Δ/SODDΔ exhibited increased susceptibility to various oxidizing agents and triazole antifungals. In addition, the loss of SodD resulted in an increased intracellular killing of the conidia by M1 macrophages derived from human blood monocytes, suggesting the involvement of this superoxide dismutase in the evasion to the host defenses. Nevertheless, one cannot disregard an indirect role of the enzyme in the synthesis or assembly of the cell wall components since transmission electron microscopic analysis revealed a thickening of the inner cell wall layer of the conidia. Further studies are needed to confirm the role of this enzyme in the pathogenesis of Scedosporium infections, including the production of a recombinant protein and study of its protective effect against the infection in a mouse model of scedosporiosis.