Establishment of a new and efficient Agrobacterium-mediated transformation system in the nematicidal fungus Purpureocillium lilacinum

Upgraded cellulose and xylan digestions for synergistic enhancements of biomass enzymatic saccharification and bioethanol conversion using engineered Trichoderma reesei strains overproducing mushroom LeGH7 enzyme

Crop straws provide enormous lignocellulose resources transformable for sustainable biofuels and valuable bioproducts. However, lignocellulose recalcitrance basically restricts essential biomass enzymatic saccharification at large scale. In this study, the mushroom-derived cellobiohydrolase (LeGH7) was introduced into Trichoderma reesei (Rut-C30) to generate two desirable strains, namely GH7-5 and GH7-6. Compared to the Rut-C30 strain, both engineered strains exhibited significantly enhanced enzymatic activities, with β-glucosidases, endocellulases, cellobiohydrolases, and xylanase activities increasing by 113 %, 140 %, 241 %, and 196 %, respectively. By performing steam explosion and mild alkali pretreatments with mature straws of five bioenergy crops, diverse lignocellulose substrates were effectively digested by the crude enzymes secreted from the engineered strains, leading to the high-yield hexoses released for bioethanol production. Notably, the LeGH7 enzyme purified from engineered strain enabled to act as multiple cellulases and xylanase at higher activities, interpreting how synergistic enhancement of enzymatic saccharification was achieved for distinct lignocellulose substrates in major bioenergy crops. Therefore, this study has identified a novel enzyme that is active for simultaneous hydrolyses of cellulose and xylan, providing an applicable strategy for high biomass enzymatic saccharification and bioethanol conversion in bioenergy crops.

Analysis of Nuclear Dynamics in Nematode-Trapping Fungi Based on Fluorescent Protein Labeling

Nematophagous fungi constitute a category of fungi that exhibit parasitic behavior by capturing, colonizing, and poisoning nematodes, which are critical factors in controlling nematode populations in nature, and provide important research materials for biological control. Arthrobotrys oligospora serves as a model strain among nematophagous fungi, which begins its life as conidia, and then its hyphae produce traps to capture nematodes, completing its lifestyle switch from saprophytic to parasitic. There have been many descriptions of the morphological characteristics of A. oligospora lifestyle changes, but there have been no reports on the nuclear dynamics in this species. In this work, we constructed A. oligospora strains labeled with histone H2B-EGFP and observed the nuclear dynamics from conidia germination and hyphal extension to trap formation. We conducted real-time imaging observations on live cells of germinating and extending hyphae and found that the nucleus was located near the tip. It is interesting that the migration rate of this type of cell nucleus is very fast, and we speculate that this may be related to the morphological changes involved in the transformation to a predatory lifestyle. We suggest that alterations in nuclear shape and fixation imply the immediate disruption of the interaction with cytoskeletal mechanisms during nuclear migration. In conclusion, these findings suggest that the signal initiating nuclear migration into fungal traps is generated at the onset of nucleus entry into a trap cell. Our work provides a reference for analysis of the dynamics of nucleus distribution and a means to visualize protein localization and interactions in A. oligospora.

Agrobacterium tumefaciens-mediated transformation of the white-rot fungus Dichomitus squalens

Dichomitus squalens is an efficient white-rot fungus that generates a wide range of extracellular enzymes to degrade lignocellulose in nature. Although a protoplast-mediated transformation method for D. squalens has been developed, the transformation efficiency remains low. Here, we established a highly efficient Agrobacterium tumefaciens-mediated transformation (ATMT) procedure for D. squalens by transferring a binary vector harboring the neomycin phosphotransferase II (nptII) resistance gene fused with DsRed-Express2, under the control of the native glyceraldehyde-3-phosphate dehydrogenase (GPD) gene promoter. Key factors affecting the efficiency of transformation were tested. A. tumefaciens EHA105 strain with a cell density of 0.4 OD600nm and 96 h co-cultivation resulted in the highest transformation efficiency, with an average of 98 ± 11 transformants per co-cultivation plate. Besides, the strong expression of DsRed-Express2 indicates the effectiveness of the DsGPD promoter in driving gene expression in D. squalens. This ATMT system of D. squalens would be beneficial for its molecular genetic studies.

Identifying pathogenicity-related genes in the pathogen Colletotrichum magnum causing watermelon anthracnose disease via T-DNA insertion mutagenesis

Fruit rot caused by Colletotrichum magnum is a crucial watermelon disease threatening the production and quality. To understand the pathogenic mechanism of C. magnum, we optimized the Agrobacterium tumefaciens-mediated transformation system (ATMT) for genetic transformation of C. magnum. The transformation efficiency of ATMT was an average of around 245 transformants per 100 million conidia. Southern blot analysis indicated that approximately 75% of the mutants contained a single copy of T-DNA. Pathogenicity test revealed that three mutants completely lost pathogenicity. The T-DNA integration sites (TISs) of three mutants were Identified. In mutant Cm699, the TISs were found in the intron region of the gene, which encoded a protein containing AP-2 complex subunit σ, and simultaneous gene deletions were observed. Two deleted genes encoded the transcription initiation protein SPT3 and a hypothetical protein, respectively. In mutant Cm854, the TISs were found in the 5'-flanking regions of a gene that was similar to the MYO5 encoding Myosin I of Pyricularia oryzae (78%). In mutant Cm1078, the T-DNA was integrated into the exon regions of two adjacent genes. One was 5'-3' exoribonuclease 1 encoding gene while the other encoded a WD-repeat protein retinoblastoma binding protein 4, the homolog of the MSl1 of Saccharomyces cerevisiae.

An efficient Agrobacterium-mediated system based on the pyrG auxotrophic marker for recombinant expression in the filamentous fungus Penicillium rubens

OBJECTIVES

This work aimed to construct a versatile, effective, and food-grade Agrobacterium tumefaciens-mediated transformation (ATMT) system for recombinant expression in the filamentous fungus Penicillium rubens (also known as Pencillium chrysogenum).

RESULTS

In this study, the wild-type P. chrysogenum VTCC 31172 strain was re-classified as P. rubens by a multilocus sequencing analysis. Further, the pyrG gene required for uridine/uracil biosynthesis was successfully deleted in the VTCC 31172 strain by homologous recombination to generate a stable uridine/uracil auxotrophic mutant (ΔpyrG). The growth of the P. rubens ΔpyrG strain could be restored by uridine/uracil supplementation, and a new ATMT system based on the uridine/uracil auxotrophic mechanism was established for this strain. The optimal ATMT efficiency could reach 1750 transformants for 10⁶ spores (equivalent to 0.18%). In addition, supplementation of uridine/uracil at the concentrations of 0.005-0.02% during the co-cultivation process significantly promoted transformation efficiency. Especially, we demonstrated that the pyrG marker and the amyB promoter from the koji mold Aspergillus oryzae were fully functional in P. rubens ΔpyrG. Expression of the DsRed reporter gene under the regulation of the A. oryzae amyB promoter lighted up the mycelium of P. rubens with a robust red signal under fluorescence microscopy. Furthermore, genomic integration of multiple copies of the Aspergillus fumigatus phyA gene under the control of the amyB promoter significantly enhanced phytase activity in P. rubens.

CONCLUSIONS

The ATMT system developed in our work provides a safe genetic platform for producing recombinant products in P. rubens without using drug resistance markers.