Enhancing the Biocontrol Potential of the Entomopathogenic Fungus in Multiple Respects via the Overexpression of a Transcription Factor Gene MaSom1

Transcription Factors in Biocontrol Fungi

Transcription factors are extensively found in fungi and are involved in the regulation of multiple biological processes, including growth, development, conidiation, morphology, stresses tolerance, and virulence, as well as the production of secondary metabolites. Biocontrol is a complex biological process through which several biocontrol behaviors, such as the secretion of cell wall-degrading enzymes and the production of secondary metabolites, are regulated by transcription factors. To date, biocontrol-related transcription factors have been reported in several biocontrol fungi, such as Beauveria bassiana, Clonostachys rosea, Coniothyrium minitans, and different species in the genera Metarhizium, Trichoderma, and Arthrobotrys. However, comprehensive reviews summarizing and analyzing transcription factors with biocontrol potential in these fungi are scarce. This review begins by giving a basic overview of transcription factors and their functions. Then, the role of biocontrol-related transcription factors in biocontrol fungi is discussed. Lastly, possible approaches for further work on transcription factors in biocontrol fungi are suggested. This review provides a basis for further elaborating the molecular mechanisms of transcription factors in the context of biocontrol.

Neg1 overexpression in Trichoderma harzianum T4 enhanced its ability to produce spores and antagonistic activity against phytopathogenic fungi

Trichoderma harzianum T4 is a soil fungus that plays an important role in the biological control of plant diseases. The aim of this study was to functionally characterize the β-1,6-glucanase gene Neg1 in T. harzianum T4 and to investigate the effect of its overexpression on biocontrol traits, especially antagonism against pathogenic fungi. We found that overexpression of Neg1 did not affect growth of T. harzianum but enhanced sporulation of T. harzianum T4 cultures. Generally, spores are closely related to the defense ability of defense fungi and can assist their proliferation and improve their colonization ability. Secondly, overexpression of Neg1 also increased the secretion level of various hydrolytic enzymes and enhanced the antagonistic ability against phytopathogenic fungi of Fusarium spp. The results suggest that Neg1 is a key gene for improving the biocontrol effect of T. harzianum T4, which contributes to a better understanding of the mechanism of action of T. harzianum T4 as a fungal biocontrol agent.

Trichosporon asahii PLA2 Gene Enhances Drug Resistance to Azoles by Improving Drug Efflux and Biofilm Formation

Trichosporon asahii is an opportunistic pathogen that can cause severe or even fatal infections in patients with low immune function. sPLA2 plays different roles in different fungi and is also related to fungal drug resistance. However, the mechanism underlying its drug resistance to azoles has not yet been reported in T. asahii. Therefore, we investigated the drug resistance of T. asahii PLA2 (TaPLA2) by constructing overexpressing mutant strains (TaPLA2^OE). TaPLA2^OE was generated by homologous recombination of the recombinant vector pEGFP-N1-TaPLA2, induced by the CMV promoter, with Agrobacterium tumefaciens. The structure of the protein was found to be typical of sPLA2, and it belongs to the phospholipase A2_3 superfamily. TaPLA2^OE enhanced antifungal drug resistance by upregulating the expression of effector genes and increasing the number of arthrospores to promote biofilm formation. TaPLA2^OE was highly sensitive to sodium dodecyl sulfate and Congo red, indicating impaired cell wall integrity due to downregulation of chitin synthesis or degradation genes, which can indirectly affect fungal resistance. In conclusion, TaPLA2 overexpression enhanced the resistance to azoles of T. asahii by enhancing drug efflux and biofilm formation and upregulating HOG-MAPK pathway genes; therefore, it has promising research prospects.

N-terminal zinc fingers of MaNCP1 contribute to growth, stress tolerance, and virulence in Metarhizium acridum

C2H2 zinc finger proteins (ZFPs) are a class of important transcriptional regulators in eukaryotes involved in multiple biological regulation processes. Here, MaNCP1, a C2H2 ZFP, was functionally characterized in the model entomopathogenic fungus Metarhizium acridum. Deletion of MaNCP1 delayed conidial germination and hyphal growth, decreased the conidial yield and reduced the tolerances to UV-B irradiation and heat-shock. The N-terminal zinc fingers (ZFs) of MaNCP1 made the main contributions to these traits. In addition, disruption of MaNCP1 altered the conidial surface structure and decreased the conidial hydrophobicity. Bioassays showed that the virulence of the MaNCP1-disruption strain (ΔMaNCP1) was reduced in topical inoculation compared to the WT or the mutant complemented strain (CP), and the N-terminal C2H2 ZFs made a major contribution to virulence. Furthermore, the ΔMaNCP1 and C2H2 ZFs deletion mutants (MaNCP1^∆N and MaNCP1^∆N+C) impaired cuticular penetration. RNA-seq showed that several cuticle-degrading genes were down-regulated in the ΔMaNCP1 background, suggesting that MaNCP1 plays vital roles in regulating insect cuticle penetration. In summary, MaNCP1 affected the growth, stress tolerances and virulence of M. acridum, and the N-terminal C2H2 ZFs played indispensable roles in these important biocontrol traits. These results provide further insights into the functions of C2H2 ZFPs in entomopathogenic fungi.