A highly efficient stratagem for protoplast isolation and genetic transformation in filamentous fungus Colletotrichum falcatum

PEG-Mediated Protoplast Transformation of Penicillium sclerotiorum (scaumcx01): Metabolomic Shifts and Root Colonization Dynamics

Protoplast-based transformation is a vital tool for genetic studies in fungi, yet no protoplast method existed for P. sclerotiorum-scaumcx01 before this study. Here, we optimized protoplast isolation, regeneration, and transformation efficiency. The highest protoplast yield (6.72 × 106 cells/mL) was obtained from liquid mycelium after 12 h of enzymatic digestion at 28 °C using Lysing Enzymes, Yatalase, cellulase, and pectinase. Among osmotic stabilizers, 1 M MgSO4 yielded the most viable protoplasts. Regeneration occurred via direct mycelial outgrowth and new protoplast formation, with a 1.02% regeneration rate. PEG-mediated transformation with a hygromycin resistance gene and GFP tagging resulted in stable GFP expression in fungal spores and mycelium over five generations. LC/MS-based metabolomic analysis revealed significant changes in glycerophospholipid metabolism, indicating lipid-related dynamics influenced by GFP tagging. Microscopy confirmed successful colonization of tomato roots by GFP-tagged scaumcx01, with GFP fluorescence observed in cortical tissues. Enzymatic (cellulase) seed pretreatment enhanced fungal colonization by modifying root surface properties, promoting plant-fungal interaction. This study establishes an efficient protoplast transformation system, reveals the metabolic impacts of genetic modifications, and demonstrates the potential of enzymatic seed treatment for enhancing plant-fungal interactions.

Comparative Genomic Analysis of Two Monokaryons of Auricularia heimuer Hei29

Auricularia heimuer is a valuable traditional Chinese fungus used as food and medicine. Hei29 is a strain derived from wild A. heimuer through systematic domestication and selection. It has been the primary A. heimuer variety in Northeast China for 30 years and offers the advantages of high yield, good commercial property, and stable traits. This study used protoplast nucleation on Hei29 to produce two amiable and paired monokaryons, Hei29-D1 and Hei29-D2. The genome of Hei29 was sequenced utilizing the Illumina PE150 and PacBio Sequel sequencing platforms. Hei29-D1 and Hei29-D2 had genomic sizes of 47.54 Mb and 47.49 Mb, GC contents of 56.95% and 56.99%, and an N50 of 2.37 Mb and 4.28 Mb, respectively. Hei29's genome possessed two phytoene synthase (PSY) protein genes, one of which-PSY encoded by g894-has a transmembrane domain. The phylogenetic tree showed that Hei29 shared the closest evolutionary relationship with Auricularia subglabra TFB-10046 SS5. Collinearity analysis showed that the correlation between the two monokaryons was as high as 90.81%. Cluster analysis revealed that Hei29 contains 12,362 core genes, 223 unique genes in Hei29-D1, and 228 unique genes in Hei29-D2. This study is the first to sequence two related and paired monokaryons from A. heimuer, which is critical for fully understanding the genetic composition and information of the characteristic strain of A. heimuer in Northeast China. It establishes the data and theoretical foundation for gene mining, usage, and molecular breeding. It further promotes the genetic breeding and active substance utilization of A. heimuer.

Exploration of the pneumocandin biosynthetic gene cluster based on efficient CRISPR/Cas9 gene editing strategy in Glarea lozoyensis

Pneumocandin B0 (PB0) is a lipopeptide produced by the fungus Glarea lozoyensis. The existing challenges with the low-yield and the extended-fermentation cycle emphasize necessity for strain improvement. In this study, we optimized conditions to obtain high-quality protoplasts and screened effective selection markers, leading to the construction of three CRISPR/Cas9 gene editing systems. Utilizing a constitutive Cas9 expression recipient strain, combined with dual sgRNAs targeting, we achieved highly efficient editing of target genes. We successfully knocked out 10 genes within the pneumocandin putative biosynthetic gene cluster and analyzed their roles in PB0 production. Our findings reveal that 4 of 10 genes are directly involved in PB0 production. Specially, the deletion of gltrt or gl10050 resulted in reduced PB0 production, while the absence of glhyp or glhtyC led to the complete loss of PB0 biosynthesis. Notably, the deletion of glhyp caused the silencing of nearly all cluster genes, whereas overexpression of glhyp led to a 2.38-fold increase in PB0 production. Therefore, this study provides the first comprehensive exploration of the functions of 10 genes within the pneumocandin putative biosynthetic gene cluster. Our findings provide valuable technical strategies for constructing bioengineering strains with purposefully enhanced PB0 production.

The Mechanism of Transcription Factor Swi6 in Regulating Growth and Pathogenicity of Ceratocystis fimbriata: Insights from Non-Targeted Metabolomics

Ceratocystis fimbriata (C. fimbriata) is a notorious pathogenic fungus that causes sweet potato black rot disease. The APSES transcription factor Swi6 in fungi is located downstream of the cell wall integrity (CWI)-mitogen-activated protein kinase (MAPK) signaling pathway and has been identified to be involved in cell wall integrity and virulence in several filamentous pathogenic fungi. However, the specific mechanisms by which Swi6 regulates the growth and pathogenicity of plant pathogenic fungi remain elusive. In this study, the SWI6 deletion mutants and complemented strains of C. fimbriata were generated. Deletion of Swi6 in C. fimbriata resulted in aberrant growth patterns. Pathogenicity assays on sweet potato storage roots revealed a significant decrease in virulence in the mutant. Non-targeted metabolomic analysis using LC-MS identified a total of 692 potential differentially accumulated metabolites (PDAMs) in the ∆Cfswi6 mutant compared to the wild type, and the results of KEGG enrichment analysis demonstrated significant enrichment of PDAMs within various metabolic pathways, including amino acid metabolism, lipid metabolism, nucleotide metabolism, GPI-anchored protein synthesis, and ABC transporter metabolism. These metabolic pathways were believed to play a crucial role in mediating the growth and pathogenicity of C. fimbriata through the regulation of CWI. Firstly, the deletion of the SWI6 gene led to abnormal amino acid and lipid metabolism, potentially exacerbating energy storage imbalance. Secondly, significant enrichment of metabolites related to GPI-anchored protein biosynthesis implied compromised cell wall integrity. Lastly, disruption of ABC transport protein metabolism may hinder intracellular transmembrane transport. Importantly, this study represents the first investigation into the potential regulatory mechanisms of SWI6 in plant filamentous pathogenic fungi from a metabolic perspective. The findings provide novel insights into the role of SWI6 in the growth and virulence of C. fimbriata, highlighting its potential as a target for controlling this pathogen.

Development of Cordyceps javanica BE01 with enhanced virulence against Hyphantria cunea using polyethylene glycol-mediated protoplast transformation

Cordyceps javanica has promising application prospects as an entomopathogenic fungus with a wide range of hosts. To enhance the virulence of C. javanica, a polyethylene glycol (PEG)-mediated protoplast genetic transformation system was constructed. Strains overexpressing the subtilisin-like protease genes CJPRB and CJPRB1 and the tripeptidyl peptidase gene CJCLN2-1 were constructed with this system, and the effects of these strains on Hyphantria cunea were tested. The aminoglycoside G418 was used at 800 μg ml⁻¹ to screen the transformants. C. javanica hyphae were degraded with an enzyme mixture to obtain protoplasts at 1.31 × 10⁷ protoplasts ml⁻¹. The transformation of 2 μg of DNA into 1,000 protoplasts was achieved with 20% PEG2000, and after 6 h of recovery, the transformation efficiency was 12.33 ± 1.42 transformants μg⁻¹ plasmid. The LT₅₀ values of CJPRB, CJPRB1, and CJCLN2-1-overexpressing C. javanica strains were 1.32-fold, 2.21-fold, and 2.14-fold higher than that of the wild-type (WT) strain, respectively. The three overexpression strains showed no significant differences from the WT strain in terms of colony growth, conidial yield, and conidial germination rate. However, the infection rate of the CJPRB1 strain was faster than that of the WT strain, with infection occurring within 4–5 days. The CJCLN2-1 strain had a significantly higher mortality rate than the WT strain within 4–10 days after infection. A C. javanica genetic transformation system was successfully constructed for the first time, and an overexpression strain exhibited enhanced virulence to H. cunea compared with the WT strain.