GATA-type transcription factor MrNsdD regulates dimorphic transition, conidiation, virulence and microsclerotium formation in the entomopathogenic fungus Metarhizium rileyi

cAMP Signalling Pathway in Biocontrol Fungi

Biocontrol is a complex process, in which a variety of physiological and biochemical characteristics are altered. The cAMP signalling pathway is an important signal transduction pathway in biocontrol fungi and consists of several key components. The G-protein system contains G-protein coupled receptors (GPCRs), heterotrimeric G-proteins, adenylate cyclase (AC), cAMP-dependent protein kinase (PKA), and downstream transcription factors (TFs). The cAMP signalling pathway can regulate fungal growth, development, differentiation, sporulation, morphology, secondary metabolite production, environmental stress tolerance, and the biocontrol of pathogens. However, few reviews of the cAMP signalling pathway in comprehensive biocontrol processes have been reported. This work reviews and discusses the functions and applications of genes encoding each component in the cAMP signalling pathway from biocontrol fungi, including the G-protein system components, AC, PKA, and TFs, in biocontrol behaviour. Finally, future suggestions are provided for constructing a complete cAMP signalling pathway in biocontrol fungi containing all the components and downstream effectors involved in biocontrol behavior. This review provides useful information for the understanding the biocontrol mechanism of biocontrol fungi by utilising the cAMP signalling pathway.

MaNsdD regulates conidiation negatively by inhibiting the AbaA expression required for normal conidiation in Metarhizium acridum

Conidiation necessary for filamentous fungal survival and dispersal, proceeds in two fashions, namely normal conidiation through conidiophores differentiated from hyphae, and microcycle conidiation through conidial budding. Normal conidiation has been well studied whereas mechanisms underlying microcycle conidiation are still largely unknown. Here, we report that a gene (MaNsdD) homologous to NsdD in Aspergillus nidulans serves as a suppressor of normal conidiation but a positive regulator of hyphal development in Metarhizium acridum. Disruption of MaNsdD (ΔMaNsdD) resulted in microcycle conidiation and significantly descended in conidial resistance to heat while improved to UV irradiation. Transcriptomic analysis revealed that many genes involved in conidiation, cell division and cell wall formation were differentially expressed in ΔMaNsdD, and likely associated with the conidiation process. We found that a gene (MaAbaA) homologous to the core asexual development regulator AbaA in A. nidulans, was negatively controlled by MaNsdD. Disruption of MaAbaA led to the abolition of the conidiation process of M. acridum. These findings unravel a novel regulatory mechanism of microcycle conidiation, and add a knowledge to the asexual conidiation pathway of filamentous fungi.

Functional characterization of the GATA-type transcription factor PaNsdD in the filamentous fungus Podospora anserina and its interplay with the sterigmatocystin pathway

The model ascomycete Podospora anserina, distinguished by its strict sexual development, is a prolific but yet unexploited reservoir of natural products. The GATA-type transcription factor NsdD has been characterized by the role in balancing asexual and sexual reproduction and governing secondary metabolism in filamentous fungi. In the present study, we functionally investigated the NsdD ortholog PaNsdD in P. anserina. Compared to the wild-type strain, vegetative growth, ageing processes, sexual reproduction, stress tolerance, and interspecific confrontations in the mutant were drastically impaired, owing to the loss of function of PaNsdD. In addition, the production of 3-acetyl-4-methylpyrrole, a new metabolite identified in P. anserina in this study, was significantly inhibited in the ΔPaNsdD mutant. We also demonstrated the interplay of PaNsdD with the sterigmatocystin biosynthetic gene pathway, especially as the deletion of PaNsdD triggered the enhanced red-pink pigment biosynthesis that occurs only in the presence of the core polyketide synthase-encoding gene PaStcA of the sterigmatocystin pathway. Taken together, these results contribute to a better understanding of the global regulation mediated by PaNsdD in P. anserina, especially with regard to its unexpected involvement in the fungal ageing process and its interplay with the sterigmatocystin pathway.

IMPORTANCE Fungal transcription factors play an essential role in coordinating multiple physiological processes. However, little is known about the functional characterization of transcription factors in the filamentous fungus Podospora anserina. In this study, a GATA-type regulator PaNsdD was investigated in P. anserina. The results showed that PaNsdD was a key factor that can control the fungal ageing process, vegetative growth, pigmentation, stress response, and interspecific confrontations and positively regulate the production of 3-acetyl-4-methylpyrrole. Meanwhile, a molecular interaction was implied between PaNsdD and the sterigmatocystin pathway. Overall, loss of function of PaNsdD seems to be highly disadvantageous for P. anserina, which relies on pure sexual reproduction in a limited life span. Therefore, PaNsdD is clearly indispensable for the survival and propagation of P. anserina in its complex ecological niches.

Transcriptome Analysis of the Japanese Pine Sawyer Beetle, Monochamus alternatus, Infected with the Entomopathogenic Fungus Metarhizium anisopliae JEF-197

The Japanese pine sawyer (JPS) beetle, Monochamus alternatus Hope (Coleoptera: Cerambycidae), damages pine trees and transmits the pine wilt nematode, Bursaphelenchus xylophilus Nickle. Chemical agents have been used to control JPS beetle, but due to various issues, efforts are being made to replace these chemical agents with entomopathogenic fungi. We investigated the expression of immune-related genes in JPS beetle in response to infection with JEF-197, a Metarhizium anisopliae isolate, using RNA-seq. RNA samples were obtained from JEF-197, JPS adults treated with JEF-197, and non-treated JPS adults on the 8th day after fungal treatment, and RNA-seq was performed using Illumina sequencing. JPS beetle transcriptome was assembled de novo and differentially expressed gene (DEG) analysis was performed. There were 719 and 1953 up- and downregulated unigenes upon JEF-197 infection, respectively. Upregulated contigs included genes involved in RNA transport, ribosome biogenesis in eukaryotes, spliceosome-related genes, and genes involved in immune-related signaling pathways such as the Toll and Imd pathways. Forty-two fungal DEGs related to energy and protein metabolism were upregulated, and genes involved in the stress response were also upregulated in the infected JPS beetles. Together, our results indicate that infection of JPS beetles by JEF-197 induces the expression of immune-related genes.

Genome-wide identification and function characterization of GATA transcription factors during development and in response to abiotic stresses and hormone treatments in pepper

Pepper (Capsicum annuum L.) is an economically important vegetable crop whose production and quality are severely reduced under adverse environmental stress conditions. The GATA transcription factors belonging to type IV zinc-finger proteins, play a significant role in regulating light morphogenesis, nitrate assimilation, and organ development in plants. However, the functional characteristics of GATA gene family during development and in response to environmental stresses have not yet been investigated in pepper. In this study, a total of 28 pepper GATA (CaGATA) genes were identified. To gain an overview of the CaGATAs, we analyzed their chromosomal distribution, gene structure, conservative domains, cis-elements, phylogeny, and evolutionary relationship. We divided 28 CaGATAs into four groups distributed on 10 chromosomes, and identified 7 paralogs in CaGATA family of pepper and 35 orthologous gene pairs between CaGATAs and Arabidopsis GATAs (AtGATAs). The results of promoter cis-element analysis and the quantitative real-time PCR (qRT-PCR) analysis revealed that CaGATA genes were involved in regulating the plant growth and development and the responses to various abiotic stresses and hormone treatments in pepper. Tissue-specific expression analysis showed that most CaGATA genes were preferentially expressed in flower buds, flowers, and leaves. Several CaGATA genes, especially CaGATA14, were significantly regulated under multiple abiotic stresses, and CaGATA21 and CaGATA27 were highly responsive to phytohormone treatments. Taken together, our results lay a foundation for the biological function analysis of GATA gene family in pepper.