Transcription factor VmSeb1 is required for the growth, development, and virulence in Valsa mali

VmSom1 is essential for growth, development, maintenance of cell wall integrity and virulence in Valsa mali

Apple Valsa canker disease, caused by Valsa mali Miyabe et Yamada, severely endangers the healthy growth of apple trees. The Som1, located downstream of the cyclic AMP-dependent protein kinase A (cAMP-PKA) pathway, plays crucial roles in the growth, development, morphological differentiation, and virulence of filamentous fungi. In this study, we identify and functionally characterize VmSom1, a homolog of Som1, in Valsa mali. The VmSom1 gene is located on chromosome 12, encoding an 824 amino acid protein. Phylogenetic analysis reveals VmSom1 as a fungal Som1 homolog. The VmSom1 deletion mutants exhibit slower growth rates and fail to produce pycnidia. Additionally, their hyphal growth is significantly inhibited on media containing Calcofluor White, Congo Red, NaCl, and sorbitol. The growth rate of VmSom1 deletion mutants is reduced on maltose, lactose, sucrose and fructose media but increases on glucose medium. Moreover, the mycelial growth rate of the VmSom1 deletion mutant is significantly lower than that of the wild-type strain in peptone, NH4SO4, NaNO3, and no nitrogen. Notably, the distances between the septa increase, and chitin concentration shifts to the hyphal tip in the VmSom1 deletion mutant. Furthermore, compared with the wild-type strain, the VmSom1 deletion mutant exhibits fewer diseased spots on apple fruit and branches. Overall, our findings demonstrate that VmSom1 is involved in regulating the growth and development, colony surface hydrophobicity, osmotic stress, cell wall integrity maintenance, carbon and nitrogen source utilization, septa formation, and virulence of V. mali.

Identification of a transcription factor AoMsn2 of the Hog1 signaling pathway contributes to fungal growth, development and pathogenicity in Arthrobotrys oligospora

INTRODUCTION

Arthrobotrys oligospora has been utilized as a model strain to study the interaction between fungi and nematodes owing to its ability to capture nematodes by developing specialized traps. A previous study showed that high-osmolarity glycerol (Hog1) signaling regulates the osmoregulation and nematocidal activity of A. oligospora. However, the function of downstream transcription factors of the Hog1 signaling in the nematode-trapping (NT) fungi remains unclear.

OBJECTIVE

This study aimed to investigate the functions and potential regulatory network of AoMsn2, a downstream transcription factor of the Hog1 signaling pathway in A. oligospora.

METHODS

The function of AoMsn2 was characterized using targeted gene deletion, phenotypic experiments, real-time quantitative PCR, RNA sequencing, untargeted metabolomics, and yeast two-hybrid analysis.

RESULTS

Loss of Aomsn2 significantly enlarged and swollen the hyphae, with an increase in septa and a significant decrease in nuclei. In particular, spore yield, spore germination rate, traps, and nematode predation efficiency were remarkably decreased in the mutants. Phenotypic and transcriptomic analyses revealed that AoMsn2 is essential for fatty acid metabolism and autophagic pathways. Additionally, untargeted metabolomic analysis identified an important function of AoMsn2 in the modulation of secondary metabolites. Furtherly, we analyzed the protein interaction network of AoMsn2 based on the Kyoto Encyclopedia of Genes and Genomes pathway map and the online website STRING. Finally, Hog1 and six putative targeted proteins of AoMsn2 were identified by Y2H analysis.

CONCLUSION

Our study reveals that AoMsn2 plays crucial roles in the growth, conidiation, trap development, fatty acid metabolism, and secondary metabolism, as well as establishes a broad basis for understanding the regulatory mechanisms of trap morphogenesis and environmental adaptation in NT fungi.

Comparative study of three cultivars of jaboticaba berry: nutrient, antioxidant and volatile compounds

Jaboticaba is a tropical plant and its fruit rich in nutrients, volatile compounds, and biological activities, which considered to be an edible health benefits plant. Despite its popularity for fresh consumption, jaboticaba is rarely used in intensive processing in China. The content of nutrients and antioxidant in jaboticaba greatly impacts how it is processed healthy food. In this study, we evaluated the nutrients, antioxidant capacity, and volatile compounds of three jaboticaba cultivars including Sabara, Argentina, and Fukuoka, respectively. Our results revealed each variety has its merits. Sabara had an abundance of volatile compounds, a suitable acid-sugar ratio, and a slightly lower antioxidant capacity, making it suitable for fresh consumption. Argentina is the richest in volatile compounds in ripe fruit, but slightly lighter in taste and acid-sugar ratio, making it suitable for dry products. The large size, juicy flesh, low acid-sugar ratio, and less volatile compounds content of Fukuoka also make it suitable for juice processing. Three cultivars of jaboticaba berry exhibited different characteristics, providing reference evidence for the manufacturing and processing of jaboticaba health food.

Transcription Factor VM1G_06867: A Requirement for Growth, Pathogenicity, Development, and Maintenance of Cell Wall Integrity in Valsa mali

Apple canker disease, caused by Valsa mali, is one of the most serious apple tree diseases in China. VmSom1 is an important transcription factor that acts on the cyclic adenosine signaling pathway (cAMP/PKA), regulating the growth, development, morphological differentiation, and pathogenic forces of the pathogen. We perform transcriptome analysis of the VmSom1 deletion mutant and the wild-type strain 11-175 and identify a significantly differentially expressed gene, VM1G_06867, a zinc finger motif transcription factor in V. mali. In this study, we obtain the VM1G_06867 gene using the single deletion mutant via homologous recombination. To determine the relationship between VmSom1 and VM1G_06867, we also obtain a double deletion mutant ΔVmSom1/06867. Compared to the wild-type strain 11-175, the single deletion mutant VM1G_06867 shows a drastic reduction in growth rate and forms more pycnidia on the PDA medium. Additionally, the growth of the mutant is inhibited by SDS, Congo red, and fluorescent brighteners. In comparison to the single deletion mutant VmSom1, the double deletion mutant ΔVmSom1/06867 shows no significant change in growth or conidiation and is unable to produce conidia. The growth rate is significantly increased in Congo red, NaCl, and Sorbitol mediums. These results demonstrate that VM1G_06867 plays important roles in growth, pathogenicity, asexual development, and maintenance of cell wall integrity. VM1G_06867 can recover osmotic stress and cell wall integrity defects caused by the deletion of VmSom1, as well as restore the loss of pathogenicity caused by the deletion of the VmSom1 gene, but not completely.

Antifungal Activity of 6-Methylcoumarin against Valsa mali and Its Possible Mechanism of Action

Valsa canker of apple (VCA) caused by Valsa mali severely affected apple production in east Asia. With the increase in drug resistance, there is an urgent need for efficient and environmentally friendly antifungal agents. Coumarins have attracted much attention due to their excellent antimicrobial activity against plant pathogens. In this study, the antifungal activity of several coumarins against phytopathogenic fungi was evaluated, and then the antifungal activity of the screened 6-MCM against V. mali and its underlying mechanism was further investigated. The results of the in vitro antifungal activity assay showed that some coumarins had significant inhibitory effects on V. mali. Notably, 400 mg/L of 6-MCM had the best antifungal activity of 94.6%. Further experiments showed that 6-MCM slowed down the growth of V. mali mycelia and the germination of spores in a concentration-dependent manner, with EC₅₀ of 185.49 and 54.62 mg/L, respectively. In addition, 6-MCM treatment increased mycelial conductivity, extracellular protein leakage, and MDA content, resulting in damage to the cell membrane. Moreover, 6-MCM significantly reduced the cell wall degrading enzymes secreted by V. mali, including EG, PG and PL, thereby limiting its pathogenic capacity. SEM and TEM results showed that 6-MCM treatment had a significant effect on the morphology and ultrastructure of mycelial cells. Inoculation of isolated apple branches found that the application of 6-MCM effectively inhibited the development of VCA and significantly reduced the incidence. All these results suggest that 6-MCM has the potential as a green substitute for VCA control.

Combinatorial strategies for production improvement of anti-tuberculosis antibiotics ilamycins E1/E2 from deep sea-derived Streptomyces atratus SCSIO ZH16 ΔilaR

Ilamycins E1/E2 are novel cyclic heptapeptides from Streptomyces atratus SCSIO ZH16, which have the MIC value of 9.8 nM against Mycobacterium tuberculosis H37Rv. However, the lower fermentative titer of ilamycins E1/E2 cut off further development for novel anti-TB lead drugs. In order to break the obstacle, the combinatorial strategy of medium optimization, fermentative parameters optimization, exogenous addition of metal ions, precursors, and surfactants was developed to promoted the production of ilamycins E1/E2. Addition of 1 mM ZnCl2 at 0 h, 1 g/L tyrosine at 96 h, and 2 g/L shikimic acid at 48 h increased the production of ilamycins E1/E2 from 13.51 to 762.50 ± 23.15, 721.39 ± 19.13, and 693.83 ± 16.86 mg/L, respectively. qRT-PCR results showed that the transcription levels of key genes in Embden-Meyerhof-Parnas pathway, hexose phosphate shunt pathway, and shikimic acid pathway were upregulated. In addition, the production of ilamycins E1/E2 reached 790.34 mg/L in a 5-L bioreactor by combinatorial strategy. Combinatorial strategies were used for improving ilamycins E1/E2 production in S. atratus ΔilaR and provided a sufficient basis on further clinic development.

D-arginine Enhances the Effect of Alpha-Amylase on Disassembling Actinomyces viscosus Biofilm

Peri-implantitis is the leading cause of dental implant failure, initially raised by biofilm accumulation on the implant surface. During the development of biofilm, Actinomyces viscosus (A. viscosus) plays a pivotal role in initial attachment as well as the bacterial coaggregation of multispecies pathogens. Hence, eliminating the A. viscosus-associated biofilm is fundamental for the regeneration of the lost bone around implants. Whereas clinical evidence indicated that antimicrobials and debridement did not show significant effects on the decontamination of biofilm on the implant surface. In this study, alpha-amylase was investigated for its effects on disassembling A. viscosus biofilm. Then, in order to substantially disperse biofilm under biosafety concentration, D-arginine was employed to appraise its enhancing effects on alpha-amylase. In addition, molecular dynamics simulations and molecular docking were conducted to elucidate the mechanism of D-arginine enhancing alpha-amylase. 0.1–0.5% alpha-amylase showed significant effects on disassembling A. viscosus biofilm, with definite cytotoxicity toward MC3T3-E1 cells meanwhile. Intriguingly, 8 mM D-arginine drastically enhanced the eradication of A. viscosus biofilm biomass by 0.01% alpha-amylase with biosafety in 30 min. The exopolysaccharides of biofilm were also thoroughly hydrolyzed by 0.01% alpha-amylase with 8 mM D-arginine. The biofilm thickness and integrity were disrupted, and the exopolysaccharides among the extracellular matrix were elusive. Molecular dynamics simulations showed that with the hydrogen bonding of D-arginine to the catalytic triad and calcium-binding regions of alpha-amylase, the atom fluctuation of the structure was attenuated. The distances between catalytic triad were shortened, and the calcium-binding regions became more stable. Molecular docking scores revealed that D-arginine facilitated the maltotetraose binding process of alpha-amylase. In conclusion, these results demonstrate that D-arginine enhances the disassembly effects of alpha-amylase on A. viscosus biofilm through potentiating the catalytic triad and stabilizing the calcium-binding regions, thus providing a novel strategy for the decontamination of biofilm contaminated implant surface.

The Transcription Factor VpxlnR Is Required for the Growth, Development, and Virulence of the Fungal Pathogen Valsa pyri

Pears (Pyrus sp.) are widely cultivated in China, and their yield accounts for more than 60% of global pear production. The fungal pathogen Valsa pyri is a major causal agent of pear canker disease, which results in enormous losses of pear production in northern China. In this study, we characterized a Zn₂Cys₆ transcription factor that contains one GAL4 domain and a fungal-trans domain, which are present in VpxlnR. The vpxlnR gene expression was upregulated in the invasion stage of V. pyri. To investigate its functions, we constructed gene deletion mutants and complementary strains. We observed that the growth of the vpxlnR mutants was reduced on potato dextrose agar (PDA), Czapek plus glucose or sucrose compared with that of the wild-type strain. Additionally, vpxlnR mutants exhibited loss of function in fruiting body formation. Moreover, vpxlnR mutants were more susceptible to hydrogen peroxide (H₂O₂) and salicylic acid (SA) and were reduced in their virulence at the early infection stage. According to a previous study, VpxlnR-interacting motifs containing NRHKGNCCGM were searched in the V. pyri genome, and we obtained 354 target genes, of which 148 genes had Clusters of Orthologous Groups (COG) terms. PHI-BLAST was used to identify virulence-related genes, and we found 28 hits. Furthermore, eight genes from the 28 PHI-BLAST hits were further assessed by yeast one-hybrid (Y1H) assays, and five target genes, salicylate hydroxylase (VP1G_09520), serine/threonine-protein kinase (VP1G_03128), alpha-xylosidase (VP1G_06369), G-protein beta subunit (VP1G_02856), and acid phosphatase (VP1G_03782), could interact with VpxlnR in vivo. Their transcript levels were reduced in one or two vpxlnR mutants. Taken together, these findings imply that VpxlnR is a key regulator of growth, development, stress, and virulence through controlling genes involved in signaling pathways and extracellular enzyme activities in V. pyri. The motifs interacting with VpxlnR also provide new insights into the molecular mechanism of xlnR proteins.

The Influence of Lower Temperature Induction of Valsa mali on the Infection of Apple Trees

Apple valsa canker (AVC), caused by Valsa mali, is one of the most important diseases of apple trees in China. AVC occurred severely along with cold winter or cold spring. However, the effect of lower temperature on V. mali is poorly understood. This study evaluated the influence of lower temperature pretreatment of V. mali on the infection of apple twigs and leaves. The results showed that exposing V. mali to lower temperatures (between -10°C and 10°C) for more than 18 h significantly increased the disease severity of apple leaves and twigs, with a higher lesion area ratio (LAR), lesion length, and disease incidence (DI) than that at 25°C. In addition, cold treatment ranging from -5°C to 10°C promoted colony growth. Meanwhile, the relative expression of four cell wall degrading enzyme (CWDE)-related genes pretreated at -5°C and 5°C were significantly higher than that at 25°C. The results indicated that the virulence of V. mali mycelium is sensitive to lower temperatures. After sensing lower temperature changes, V. mali can adjust its infection of apple trees by regulating the expression of pathogenicity gene and growth rate. Spring has very frequent temperature changes, and V. mali is highly invasive in this season. Therefore, more attention should be paid in spring to protecting apple trees from infection of V. mali, by reducing pruning wound formation in spring and applying protective agents to pruning wounds in time.

Transcription factor control of virulence in phytopathogenic fungi

Plant-pathogenic fungi are a significant threat to economic and food security worldwide. Novel protection strategies are required and therefore it is critical we understand the mechanisms by which these pathogens cause disease. Virulence factors and pathogenicity genes have been identified, but in many cases their roles remain elusive. It is becoming increasingly clear that gene regulation is vital to enable plant infection and transcription factors play an essential role. Efforts to determine their regulatory functions in plant-pathogenic fungi have expanded since the annotation of fungal genomes revealed the ubiquity of transcription factors from a broad range of families. This review establishes the significance of transcription factors as regulatory elements in plant-pathogenic fungi and provides a systematic overview of those that have been functionally characterized. Detailed analysis is provided on regulators from well-characterized families controlling various aspects of fungal metabolism, development, stress tolerance, and the production of virulence factors such as effectors and secondary metabolites. This covers conserved transcription factors with either specialized or nonspecialized roles, as well as recently identified regulators targeting key virulence pathways. Fundamental knowledge of transcription factor regulation in plant-pathogenic fungi provides avenues to identify novel virulence factors and improve our understanding of the regulatory networks linked to pathogen evolution, while transcription factors can themselves be specifically targeted for disease control. Areas requiring further insight regarding the molecular mechanisms and/or specific classes of transcription factors are identified, and direction for future investigation is presented.

The Fungal-Specific Transcription Factor VpFSTF1 Is Required for Virulence in Valsa pyri

Valsa pyri is the causal agent of pear canker disease, which leads to enormous losses of pear production in eastern Asian, especially China. In this study, we identified a fungal-specific transcription factor 1 (termed as VpFSTF1) from V. pyri, which is highly conserved in fungi. To characterize its functions, we generated mutant and complementation strains in V. pyri and found that ΔVpFSTF1 mutants lost the ability to form fruiting bodies along with the reduced virulence. The radial growth of ΔVpFSTF1 mutant was sensitive to increasing concentrations of hydrogen peroxide (H₂O₂) and salicylic acid (SA). Moreover, RNA-sequencing (RNA-Seq) analysis of wild-type (WT) and ΔVpFSTF1 mutant strains was performed, and the results revealed 1,993 upregulated, and 2006 downregulated differentially expressed genes (DEGs) in the mutant. The DEGs were corresponding to the genes that are involved in amino acid metabolism, starch, and sucrose metabolism, gluconeogenesis, citrate cycle, and carbon metabolism. Interestingly, pathogen host interaction (PHI) analysis showed that 69 downregulated genes were related to virulence, suggesting that they might function downstream of VpFSTF1. Nine DEGs were further validated by quantitative reverse transcription-polymerase chain reaction (qRT-PCR), and the results were consistent with RNA-seq analysis. Furthermore, promoter regions were predicted, and VpFSTF1 binding activity was assessed. We demonstrated that five promoters are directly or indirectly targeted by VpFSTF1, including catalase-related peroxidase (VPIG_01209) and P450 family genes. Taken together, these findings indicate that VpFSTF1 is crucial for the virulence of V. pyri via direct or indirect regulation of downstream genes expression and lay an important foundation for understanding the molecular mechanism of V. pyri infection.

The Cys2His2 zinc finger protein Zfp1 regulates sexual reproduction and virulence in Cryptococcus neoformans

Cryptococcus neoformans is a ubiquitous yeast pathogen that often infects the human central nervous system (CNS) to cause meningitis in immunocompromised individuals. Although numerous signaling pathways and factors important for fungal sexual reproduction and virulence have been investigated, their precise mechanism of action remains to be further elucidated. In this study, we identified and characterized a novel zinc finger protein Zfp1 that regulates fungal sexual reproduction and virulence in C. neoformans. qRT-PCR and ZFP1 promoter regulatory activity assays revealed a ubiquitous expression pattern of ZFP1 in all stages during mating. Subcellular localization analysis indicates that Zfp1 is targeted to the cytoplasm of C. neoformans. In vitro assays of stress responses showed that zfp1Δ mutants and the ZFP1 overexpressed strains ZFP1^OE are hypersensitive to SDS, but not Congo red, indicating that Zfp1 may regulate cell membrane integrity. Zfp1 is also essential for fungal sexual reproduction because basidiospore production was blocked in bilateral mating between zfp1Δ mutants or ZFP1 overexpressed strains. Fungal nuclei development assay showed that nuclei in the bilateral mating of zfp1Δ mutants or ZFP1 overexpressed strains failed to undergo meiosis after fusion, indicating Zfp1 is important for regulating meiosis during mating. Although zfp1Δ mutants showed normal growth and produced normal major virulence factors, virulence was attenuated in a murine model. Interestingly, we found that the ZFP1 overexpressed strains were avirulent in a murine systemic-infection model. Overall, our study showed that the zinc finger protein Zfp1 is essential for fungal sporulation and virulence in C. neoformans.