Influence of PacC on the environmental stress adaptability and cell wall components of Ganoderma lucidum

Structural diversification of fungal cell wall in response to the stress signaling and remodeling during fungal pathogenesis

Fungi are one of the most diverse organisms found in our surroundings. The heterotrophic lifestyle of fungi and the ever-changing external environmental factors pose numerous challenges for their survival. Despite all adversities, fungi continuously develop new survival strategies to secure nutrition and space from their host. During host-pathogen interaction, filamentous phytopathogens in particular, effectively infect their hosts by maintaining polarised growth at the tips of hyphae. The fungal cell wall, being the prime component of host contact, plays a crucial role in fortifying the intracellular environment against the harsh external environment. Structurally, the fungal cell wall is a highly dynamic yet rigid component, responsible for maintaining cellular morphology. Filamentous pathogens actively maintain their dynamic cell wall to compensate rapid growth on the host. Additionally, they secrete effectors to dampen the sophisticated mechanisms of plant defense and initiate various downstream signaling cascades to repair the damage inflicted by the host. Thus, the fungal cell wall serves as a key modulator of fungal pathogenicity. The fungal cell wall with their associated signaling mechanisms emerge as intriguing targets for host immunity. This review comprehensively examines and summarizes the multifaceted findings of various research groups regarding the dynamics of the cell wall in filamentous fungal pathogens during host invasion.

VmPacC-mediated pH regulation of Valsa mali confers to host acidification identified by comparative proteomics analysis

Apple valsa canker caused by the Ascomycete fungus Valsa mali is one of the most serious diseases of apple, resulting in huge economic losses in the apple-growing area of China. Previous study found that the pathogen could acidify the infected tissues to make lower ambient pH (from 6.0 to 3.5) for their successfully colonization. The pH signaling transcription factor VmPacC is required for acidification of its environment and for full virulence in V. mali. It is known that the functional cooperation of proteins secreted by V. mali plays pivotal role in its successful colonization of host plants. In this study, we used tandem mass tag (TMT) labeling coupled with LC-MS/MS-based quantitative proteomics to analyze the VmPacC-mediated pH regulation in V. mali, focusing on differentially expressed proteins (DEPs). We identified 222 DEPs specific to VmPacC deletion, and 921 DEPs specific to different pH conditions (pH 6.0 and 3.4). Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses indicated that these DEPs were mainly involved in pathways associated with carbon metabolism, biosynthesis of antibiotics, citrate cycle (TCA cycle), glycolysis/gluconeogenesis, glutathione metabolism, ribosomes, and pentose phosphate pathways. Additionally, we identified 119 DEPs that were shared among the VmPacC deletion mutant and different pH conditions, which were mainly related to energy metabolism pathways, providing the energy required for the hyphal growth and responses to environmental stresses. A protein-protein interaction (PPI) network analysis indicated that most of the shared proteins were mapped to an interaction network with a medium confidence score of 0.4. Notably, one uncharacterized protein (KUI69106.1), and two known proteins (heat shock protein 60 (KUI73579.1), aspartate aminotransferase (KUI73864.1)) located in the core of the network were highly connected (with ≥ 38 directed edges) with the other shared DEPs. Our results suggest that VmPacC participates in the pathogen's regulation to ambient pH through the regulation of energy metabolism pathways such as the glycolysis/gluconeogenesis pathway and TCA cycle. Finally, we proposed a sophisticated molecular regulatory network to explain pH decrease in V. mali. Our study, by providing insights into V. mali regulating pH, helps to elucidate the mechanisms of host acidification during pathogen infection.

The role of pH transcription factor Appacc in upregulation of pullulan biosynthesis in Aureobasidium pullulans using potato waste as a substrate

pH is one of the important environmental factors affecting the growth, development and secondary metabolites of fungi. To better utilize potato waste for the production of pullulan by fermentation, in this study, the amino acid sequence and structural domain of pH transcription factor Appacc were analyzed using the bioinformatics methods. Appacc showed three typically conserved zinc finger domains, with the closest homology to Zymoseptoria brevis. The function of Appacc was characterized by ΔAppacc and OEXpacc mutants. The mycelium growth of ΔApacc mutants was inhibited, especially, under alkaline conditions. Furthermore, the pullulan production of ΔAppacc mutant was reduced and the expression of pullulan synthetic genes also decreased. Moreover, the OEXpacc mutant further demonstrated that pacc could regulate the expression of pullulan synthesis genes. The yield of pullulan polysaccharide increased from 13.6 g/L to 17.8 g/L by direct fermentation without changing the pH of potato waste. These results suggest that Appacc played a vital role in the growth of Aureobasidium pullulans and that the production of pullulan from potato waste can be increased by overexpression of pacc gene.

Transcriptome profiling of transcription factors in Ganoderma lucidum in response to methyl jasmonate

Ganoderma lucidum is a traditional Chinese medicine and its major active ingredients are ganoderma triterpenoids (GTs). To screen for transcription factors (TFs) that involved in the biosynthetic pathway of GTs in G. lucidum, the chemical composition in mycelia, primordium and fruiting body were analyzed, and the transcriptomes of mycelia induced by methyl jasmonate (MeJA) were analyzed. In addition, the expression level data of MeJA-responsive TFs in mycelia, primordia and fruiting body were downloaded from the database, and the correlation analysis was carried out between their expression profiles and the content of total triterpenoids. The results showed that a total of 89 components were identified, and the content of total triterpenoids was the highest in primordium, followed by fruiting body and mycelia. There were 103 differentially expressed TFs that response to MeJA-induction including 95 upregulated and 8 downregulated genes. These TFs were classified into 22 families including C2H2 (15), TFII-related (12), HTH (9), fungal (8), bZIP (6), HMG (5), DADS (2), etc. Correlation analysis showed that the expression level of GL23559 (MADS), GL26472 (HTH), and GL31187 (HMG) showed a positive correlation with the GTs content, respectively. While the expression level of GL25628 (fungal) and GL26980 (PHD) showed a negative correlation with the GTs content, respectively. Furthermore, the over expression of the Glmhr1 gene (GL25628) in Pichia pastoris GS115 indicated that it might be a negative regulator of GT biosynthesis through decreasing the production of lanosterol. This study provided useful information for a better understanding of the regulation of TFs involved in GT biosynthesis and fungal growth in G. lucidum.

GCN4 Enhances the Transcriptional Regulation of AreA by Interacting with SKO1 To Mediate Nitrogen Utilization in Ganoderma lucidum

Nitrogen is an essential nutrient for cell growth and proliferation. Limitations of nitrogen availability in organisms elicit a series of rapid transcriptional reprogramming mechanisms, which involve the participation of many transcription factors.

The pH signalling transcription factor PacC modulate growth, development, stress response and pathogenicity of Trichothecium roseum

pH is one of the important environmental factors that affect the growth, development and pathogenicity of postharvest pathogen. The transcription factor PacC dominates the pH signal pathway. PacC in Trichothecium roseum showed three typical conserved zinc finger domains and closest homology to Fusarium graminearum. T. roseum increased the environmental pH both in vitro and in vivo. Expression patterns of TrpacC under different pH showed that at increasing pH from 3 to 5, the wild-type (WT) strain induced the expression of TrPacC in parallel to increased fungal growth; however, TrPacC expression decline at higer pH than 5, while fungal growth continued to increase. Development of a ΔTrPacC mutant down-regulated the expression of TrbrlA, TrabaA and TrwetA, reduced sporulation and delayed spore germination, resulting in smaller spores and sparse hyphae. ΔTrPacC mutant was sensitive to ionic stress, oxidative stress and cell wall integrity stress compared to the WT strain, especially the ionic stress. In addition, ∆TrPacC mutant showed reduced pathogenicity to muskmelon and tomato fruits. Taken together, T. roseum is an alkalinizing fungus, and the acidic environment could induce TrPacC expression. TrPacC positively regulates fungal growth and development as well as pathogenicity showing effect on fungal response to different stresses.

Histone acetyltransferases MystA and MystB contribute to morphogenesis and aflatoxin biosynthesis by regulating acetylation in fungus Aspergillus flavus

Myst family is highly conserved histone acetyltransferases in eukaryotic cells and is known to play crucial roles in various cellular processes; however, acetylation catalysed by acetyltransferases is unclear in filamentous fungi. Here, we identified two classical nonessential Myst enzymes and analysed their functions in Aspergillus flavus, which generates aflatoxin B1, one of the most carcinogenic secondary metabolites. MystA and MystB located in nuclei and cytoplasm, and mystA could acetylate H4K16ac, while mystB acetylates H3K14ac, H3K18ac and H3K23ac. Deletion mystA resulted in decreased conidiation, increased sclerotia formation and aflatoxin production. Deletion of mystB leads to significant defects in conidiation, sclerotia formation and aflatoxin production. Additionally, double-knockout mutant (ΔmystA/mystB) display a stronger and similar defect to ΔmystB mutant, indicating that mystB plays a major role in regulating development and aflatoxin production. Both mystA and mystB play important role in crop colonization. Moreover, catalytic domain MOZ and the catalytic site E199/E243 were important for the acetyltransferase function of Myst. Notably, chromatin immunoprecipitation results indicated that mystB participated in oxidative detoxification by regulating the acetylation level of H3K14, and further regulated nsdD to affect sclerotia formation and aflatoxin production. This study provides new evidences to discover the biological functions of histone acetyltransferase in A. flavus.

Evolutionary Morphogenesis of Sexual Fruiting Bodies in Basidiomycota: Toward a New Evo-Devo Synthesis

The development of sexual fruiting bodies is one of the most complex morphogenetic processes in fungi. Mycologists have long been fascinated by the morphological and developmental diversity of fruiting bodies; however, evolutionary developmental biology of fungi still lags significantly behind that of animals or plants. Here, we summarize the current state of knowledge on fruiting bodies of mushroom-forming Basidiomycota, focusing on phylogenetic and developmental biology. Phylogenetic approaches have revealed a complex history of morphological transformations and convergence in fruiting body morphologies. Frequent transformations and convergence is characteristic of fruiting bodies in contrast to animals or plants, where main body plans are highly conserved. At the same time, insights into the genetic bases of fruiting body development have been achieved using forward and reverse genetic approaches in selected model systems. Phylogenetic and developmental studies of fruiting bodies have each yielded major advances, but they have produced largely disjunct bodies of knowledge. An integrative approach, combining phylogenetic, developmental, and functional biology, is needed to achieve a true fungal evolutionary developmental biology (evo-devo) synthesis for fungal fruiting bodies.

Function of pH-dependent transcription factor PacC in regulating development, pathogenicity, and mycotoxin biosynthesis of phytopathogenic fungi

pH, as one of the most important environmental factors, affects various biological processes in pathogenic fungi. Sensing and responding to fluctuations in ambient pH are essential for these fungi to complete their life cycle. Fungi have evolved a complicated and conserved system, the so-called Pal-pH pathway, to regulate genes and adapt to alterations in ambient pH. PacC is the dominant transcription factor in the Pal-pH pathway and regulates various biological processes. The regulatory mode of PacC has been extensively studied in Aspergillus nidulans and is generally conserved in other fungal species, including numerous phytopathogenic fungi. However, species-specific alterations have been reported. This review summarizes recent advances in the regulatory mechanisms of PacC and its role in controlling development, pathogenicity, and mycotoxin biosynthesis in phytopathogenic fungi. Potential applications of these findings and some unresolved questions are also discussed.