Golgi-localized calcium/manganese transporters FgGdt1 and FgPmr1 regulate fungal development and virulence by maintaining Ca2+ and Mn2+ homeostasis in Fusarium graminearum

The nuclear pore protein Nup2 is essential for growth and development, stress response, pathogenicity and deoxynivalenol biosynthesis in Fusarium graminearum

BACKGROUND

Wheat is an important grain crop that has been under serious threat from Fusarium graminearum. Nup2, a member of the nuclear pore complex, plays an important role in regulating eukaryotic nuclear protein transport and participates in gene regulation. Dissecting the function of nuclear pore proteins in pathogenic fungi may provide effective targets for novel fungicides.

RESULTS

Mutants exhibited nutritional growth defects, asexual/sexual developmental abnormalities. Deficiency of FgNup2 resulted in increased resistance of Fusarium graminearum to cell wall disruptors and increased sensitivity to metal ions. Pathogenicity analyses showed that the mutant was significantly less virulent on flowering wheat ears, consistent with the observed decrease in deoxynivalenol (DON) production. Furthermore, we showed that FgNup2 interacts synergistically with FgTri6, a transcription factor of the TRI family, to regulate the expression of toxin-producing genes, which, in turn, affects the biosynthesis of DON and related toxins.

CONCLUSION

This study revealed that FgNup2 plays important roles in the growth and development, cell wall integrity, stress response, pathogenicity, and DON synthesis of F. graminearum. © 2024 Society of Chemical Industry.

The Non-Histone Protein FgNhp6 Is Involved in the Regulation of the Development, DON Biosynthesis, and Virulence of Fusarium graminearum

Fusarium graminearum is the primary causative agent of Fusarium head blight (FHB), a devastating disease affecting cereals globally. The high-mobility group (HMG) of non-histone proteins constitutes vital architectural elements within chromatin, playing diverse roles in various biological processes in eukaryotic cells. Nonetheless, the specific functions of HMG proteins in F. graminearum have yet to be elucidated. Here, we identified 10 HMG proteins in F. graminearum and extensively characterized the biological roles of one HMGB protein, FgNhp6. We constructed the FgNhp6 deletion mutant and its complementary strains. With these strains, we confirmed the nuclear localization of FgNhp6 and discovered that the absence of FgNhp6 led to reduced radial growth accompanied by severe pigmentation defects, a significant reduction in conidial production, and a failure to produce perithecia. The ∆FgNhp6 mutant exhibited a markedly reduced pathogenicity on wheat coleoptiles and spikes, coupled with a significant increase in deoxynivalenol production. An RNA sequencing (RNA-seq) analysis indicated that FgNhp6 deletion influenced a wide array of metabolic pathways, particularly affecting several secondary metabolic pathways, such as sterol biosynthesis and aurofusarin biosynthesis. The findings of this study highlight the essential role of FgNhp6 in the regulation of the asexual and sexual reproduction, deoxynivalenol (DON) production, and pathogenicity of F. graminearum.

The Development of Aspergillus flavus and Biosynthesis of Aflatoxin B1 are Regulated by the Golgi-Localized Mn2+ Transporter Pmr1

Microorganisms rely on diverse ion transport and trace elements to sustain growth, development, and secondary metabolism. Manganese (Mn2+) is essential for various biological processes and plays a crucial role in the metabolism of human cells, plants, and yeast. In Aspergillus flavus, we confirmed that Pmr1 localized in cis- and medial-Golgi compartments was critical in facilitating Mn2+ transport, fungal growth, development, secondary metabolism, and glycosylation. In comparison to the wild type, the Δpmr1 mutant displayed heightened sensitivity to environmental stress, accompanied by inhibited synthesis of aflatoxin B1, kojic acid, and a substantial reduction in pathogenicity toward peanuts and maize. Interestingly, the addition of exogenous Mn2+ effectively rectified the developmental and secondary metabolic defects in the Δpmr1 mutant. However, Mn2+ supplement failed to restore the growth and development of the Δpmr1Δgdt1 double mutant, which indicated that the Gdt1 compensated for the functional deficiency of pmr1. In addition, our results showed that pmr1 knockout leads to an upregulation of O-glycosyl-N-acetylglucose (O-GlcNAc) and O-GlcNAc transferase (OGT), while Mn2+ supplementation can restore the glycosylation in A. flavus. Collectively, this study indicates that the pmr1 regulates Mn2+ via Golgi and maintains growth and metabolism functions of A. flavus through regulation of the glycosylation.

Permissible concentration of mancozeb in Brazilian drinking water elicits oxidative stress and bioenergetic impairments in embryonic zebrafish

Mancozeb (MZ) is widely used as a fungicide in Brazil due to its effectiveness in combating fungal infections in plantations. However, its toxicity to non-target organisms, including aquatic organisms, has been reported in the literature. Recently, Brazilian legislation was updated to allow a concentration of 8 μg/L of MZ in drinking water (Ordinance GM/MS nº 888, of May 4, 2021). However, the safety of this concentration for aquatic organisms has not yet been put to the test. To address this gap, we conducted a study using zebrafish (Danio rerio) embryos at 4 hpf exposed to MZ at the concentration allowed by law, as well as slightly higher sublethal concentrations (24, 72, and 180 μg/L), alongside a control group. We evaluated various morphophysiological markers of toxicity, including survival, spontaneous movements, heart rate, hatching rate, body axis distortion, total body length, total yolk sac area, and total eye area. Additionally, we measured biochemical biomarkers such as reactive oxygen species (ROS) levels, lipid peroxidation, non-protein thiols (NPSH), and mitochondrial bioenergetic parameters. Our results showed that the concentration of 8 μg/L, currently permitted in drinking water according to Brazilian legislation, increased ROS production levels and caused alterations in mitochondrial physiology. Among the markers assessed, mitochondrial bioenergetic function appeared to be the most sensitive indicator of MZ embryotoxicity, as a decrease in complex I activity was observed at concentrations of 8 and 180 μg/L. Furthermore, concentrations higher than 8 μg/L impaired morphophysiological markers. Based on these findings, we can infer that the concentration of MZ allowed in drinking water by Brazilian environmental legislation is not safe for aquatic organisms. Our study provides evidence that this fungicide is a potent embryotoxic agent, highlighting the potential risks associated with its exposure.

MAP Kinase FgHog1 and Importin β FgNmd5 Regulate Calcium Homeostasis in Fusarium graminearum

Maintaining cellular calcium (Ca²⁺) homeostasis is essential for many aspects of cellular life. The high-osmolarity glycerol (HOG) mitogen-activated protein kinase (MAPK) pathway responsible for signal integration and transduction plays crucial roles in environmental adaptation, especially in the response to osmotic stress. Hog1 is activated by transient Ca²⁺ increase in yeast, but the functions of the HOG pathway in Ca²⁺ homeostasis are largely unknown. We found that the HOG pathway was involved in the regulation of Ca²⁺ homeostasis in Fusarium graminearum, a devastating fungal pathogen of cereal crops. The deletion mutants of HOG pathway displayed increased sensitivity to Ca²⁺ and FK506, and elevated intracellular Ca²⁺ content. Ca²⁺ treatment induced the phosphorylation of FgHog1, and the phosphorylated FgHog1 was transported into the nucleus by importin β FgNmd5. Moreover, the increased phosphorylation and nuclear accumulation of FgHog1 upon Ca²⁺ treatment is independent of the calcineurin pathway that is conserved and downstream of the Ca²⁺ signal. Taken together, this study reported the novel function of FgHog1 in the regulation of Ca²⁺ homeostasis in F. graminearum, which advance the understanding of the HOG pathway and the association between the HOG and calcineurin pathways in fungi.