LaeA negatively regulates dothistromin production in the pine needle pathogen Dothistroma septosporum

AfLaeA, a Global Regulator of Mycelial Growth, Chlamydospore Production, Pathogenicity, Secondary Metabolism, and Energy Metabolism in the Nematode-Trapping Fungus Arthrobotrys flagrans

Arthrobotrys flagrans (Duddingtonia flagrans) is a typical nematode-trapping fungus which has been used for nematode biocontrol. The global regulator LaeA is widely distributed in filamentous fungi and plays a crucial role in secondary metabolism and development in addition to pathogenicity in fungal pathogens. In this study, the chromosome-level genome of A. flagrans CBS 565.50 was sequenced and homologous sequences of LaeA were identified in A. flagrans. A. flagrans LaeA (AfLaeA) knockout resulted in slower hyphal growth and a smoother hyphal surface. Importantly, deletion of AfLaeA resulted in the absence of chlamydospores and attenuated glycogen and lipid accumulation in hyphae. Similarly, disruption of the AfLaeA gene led to fewer traps and electron-dense bodies, lower protease activity, and a delay in capturing nematodes. The AfLaeA gene had a large effect on the secondary metabolism of A. flagrans, and both the deletion and overexpression of AfLaeA could yield new compounds, whereas some compounds were lost due to the absence of the AfLaeA. Protein-protein interactions between AfLaeA and another eight proteins were detected. Furthermore, transcriptome data analysis showed that 17.77% and 35.51% of the genes were influenced by the AfLaeA gene on days 3 and 7, respectively. AfLaeA gene deletion resulted in the higher expression level of the artA gene cluster, and multiple differentially expressed genes involved in glycogen and lipid synthesis and metabolism showed opposite expression patterns in wild-type and ΔAfLaeA strains. In summary, our results provide novel insights into the functions of AfLaeA in mycelial growth, chlamydospore production, pathogenicity, secondary metabolism, and energy metabolism in A. flagrans. IMPORTANCE The regulation of biological functions, such as the secondary metabolism, development, and pathogenicity of LaeA, has been reported in multiple fungi. But to date, no study on LaeA in nematode-trapping fungi has been reported. Moreover, it has not been investigated whether or not LaeA is involved in energy metabolism and chlamydospore formation has not been investigated. Especially in the formation mechanism of chlamydospores, several transcription factors and signaling pathways are involved in the production of chlamydospores, but the mechanism of chlamydospore formation from an epigenetic perspective has not been revealed. Concurrently, an understanding of protein-protein interactions will provide a broader perspective on the regulatory mechanism of AfLaeA in A. flagrans. This finding is critical for understanding the regulatory role of AfLaeA in the biocontrol fungus A. flagrans and establishes a foundation for developing high-efficiency nematode biocontrol agents.

Beyond the genomes of Fulvia fulva (syn. Cladosporium fulvum) and Dothistroma septosporum: New insights into how these fungal pathogens interact with their host plants

Fulvia fulva and Dothistroma septosporum are closely related apoplastic pathogens with similar lifestyles but different hosts: F. fulva is a pathogen of tomato, whilst D. septosporum is a pathogen of pine trees. In 2012, the first genome sequences of these pathogens were published, with F. fulva and D. septosporum having highly fragmented and near-complete assemblies, respectively. Since then, significant advances have been made in unravelling their genome architectures. For instance, the genome of F. fulva has now been assembled into 14 chromosomes, 13 of which have synteny with the 14 chromosomes of D. septosporum, suggesting these pathogens are even more closely related than originally thought. Considerable advances have also been made in the identification and functional characterization of virulence factors (e.g., effector proteins and secondary metabolites) from these pathogens, thereby providing new insights into how they promote host colonization or activate plant defence responses. For example, it has now been established that effector proteins from both F. fulva and D. septosporum interact with cell-surface immune receptors and co-receptors to activate the plant immune system. Progress has also been made in understanding how F. fulva and D. septosporum have evolved with their host plants, whilst intensive research into pandemics of Dothistroma needle blight in the Northern Hemisphere has shed light on the origins, migration, and genetic diversity of the global D. septosporum population. In this review, we specifically summarize advances made in our understanding of the F. fulva-tomato and D. septosporum-pine pathosystems over the last 10 years.

Complementary Strategies to Unlock Biosynthesis Gene Clusters Encoding Secondary Metabolites in the Filamentous Fungus Podospora anserina

The coprophilous ascomycete Podospora anserina is known to have a high potential to synthesize a wide array of secondary metabolites (SMs). However, to date, the characterization of SMs in this species, as in other filamentous fungal species, is far less than expected by the functional prediction through genome mining, likely due to the inactivity of most SMs biosynthesis gene clusters (BGCs) under standard conditions. In this work, our main objective was to compare the global strategies usually used to deregulate SM gene clusters in P. anserina, including the variation of culture conditions and the modification of the chromatin state either by genetic manipulation or by chemical treatment, and to show the complementarity of the approaches between them. In this way, we showed that the metabolomics-driven comparative analysis unveils the unexpected diversity of metabolic changes in P. anserina and that the integrated strategies have a mutual complementary effect on the expression of the fungal metabolome. Then, our results demonstrate that metabolite production is significantly influenced by varied cultivation states and epigenetic modifications. We believe that the strategy described in this study will facilitate the discovery of fungal metabolites of interest and will improve the ability to prioritize the production of specific fungal SMs with an optimized treatment.

CgVeA, a light signaling responsive regulator, is involved in regulation of chaetoglobosin A biosynthesis and conidia development in Chaetomium globosum

Cytochalasans, with diverse structures and pharmacological activities, are a class of compounds containing isoindolinone moieties fused to the tricyclic or tetracyclic ring system. Chaetoglobosin A (cheA), mainly produced by Chaetomium globosum, is the most abundant cytochalasan. However, limited understanding of transcriptional regulation of morphological development and cheA biosynthesis in C. globosum has hindered cheA application in agriculture and biomedical field. This study examined the regulatory role of CgVeA gene in C. globosum. CgVeA had significant effect on secondary metabolites production in C. globosum, similar to that reported in other filamentous fungi. Inactivation of CgVeA caused an obvious decrease in cheA production from 51.32 to 19.76 mg/L under dark conditions. In contrast, CgVeA overexpression resulted in a dramatic increase in cheA production, reaching 206.59 mg/L under light conditions, which was higher than that noted under dark condition. The RT-qPCR results confirmed that CgVeA, as a light responsive regulator, positively regulated cheA biosynthesis by controlling the expression of core genes of the cheA biosynthetic gene cluster and other relevant regulators. Electrophoretic mobility shift assays proved that CgVeA directly regulated LaeA, cheR, and p450, and indirectly regulated PKS. Moreover, CgVeA had a significant effect on the regulation of asexual spores production. When compared with wild-type C. globosum, CgVeA-silenced and CgVeA overexpression mutants presented remarkable differences in sporulation, irrespective of light or dark condition. Besides, CgVeA expression was speculated to negatively regulate spore formation. These findings illustrated the regulatory mechanism of a hypothetical global regulator, CgVeA, in C. globosum, suggesting its potential application in industrial-scale cheA biosynthesis.

A methyltransferase LaeA regulates ganoderic acid biosynthesis in Ganoderma lingzhi

The methyltransferase LaeA is a global regulator involved in the biosynthesis of secondary metabolites by ascomycete fungi. However, little is known of its regulatory role in basidiomycete fungi. In this study, the laeA gene was identified in the basidiomycete Ganoderma lingzhi and its function in regulating the biosynthesis of anti-tumor ganoderic acids was evaluated. A laeA deletion (ΔlaeA) Ganoderma strain exhibited significantly reduced concentration of ganoderic acids. qRT-PCR analysis further revealed that the transcription levels of genes involved in the biosynthesis of ganoderic acids were drastically lower in the ΔlaeA strain. Moreover, deletion of laeA resulted in decreased accumulation of intermediates and abundances of asexual spores in liquid static culture of G. lingzhi. In contrast, constitutive overexpression of laeA resulted in increased concentration of ganoderic acids. These results demonstrate an essential role of LaeA in the regulation of ganoderic acid biosynthesis in Ganoderma.

Functional Roles of LaeA-like Genes in Fungal Growth, Cellulase Activity, and Secondary Metabolism in Pleurotus ostreatus

The global regulator LaeA plays crucial roles in morphological development and secondary metabolite biosynthesis in filamentous fungi. However, the functions of LaeA in basidiomycetes are less reported. The basidiomycete Pleurotus ostreatus is a well-known fungus used both in medicine and as food that produces polysaccharides and cellulolytic enzymes. In this study, we characterized three LaeA homologs (PoLaeA1, PoLaeA2, and PoLaeA3) in P. ostreatus. PoLaeA1 showed different expression patterns than PoLaeA2 and PoLaeA3 during different developmental stages. Silencing PoLaeA1 decreased the intracellular polysaccharide (IPS) content by approximately 28–30% and reduced intracellular ROS levels compared with those of the WT strain. However, silencing PoLaeA2 and PoLaeA3 decreased cellulase activity by 31–34% and 35–40%, respectively, and reduced the cytosolic Ca2+ content, compared with those of the WT strain. Further analysis showed that PoLaeA1 regulated IPS biosynthesis through intracellular ROS levels, whereas PoLaeA2 and PoLaeA3 regulated cellulase activity through intracellular Ca2+ signaling. Our results provide new insights into the regulation of polysaccharide biosynthesis and cellulase production in filamentous fungi.

The regulation of BbLaeA on the production of beauvericin and bassiatin in Beauveria bassiana

Beauvericin and bassiatin are two valuable compounds with various bioactivities biosynthesized by the supposedly same nonribosomal peptide synthetase BbBEAS in entomopathogenic fungus Beauveria bassiana. To evaluate the regulatory effect of global regulator LaeA on their production, we constructed BbLaeA gene deletion and overexpression mutants, respectively. Deletion of BbLaeA resulted in a decrease of the beauvericin titer, while overexpression of BbLaeA increased its production by 1-2.26 times. No bassiatin could be detected in ΔBbLaeA and wild type strain of B. bassiana, but 4.26-5.10 µg/mL bassiatin was produced in OE::BbLaeA. Furthermore, additional metabolites with increased production in OE::BbLaeA were isolated and identified as primary metabolites. Among them, 4-hydroxyphenylacetic acid showed antibacterial bioactivity against Ralstonia solanacearum. These results indicated that BbLaeA positively regulates the production of beauvericin, bassiatin and various bioactive primary metabolites.

Whole Genome Sequence of Alternaria alternata, the Causal Agent of Black Spot of Kiwifruit

Alternaria alternata is a pathogen in a wide range of agriculture crops and causes significant economic losses. A strain of A. alternata (Y784-BC03) was isolated and identified from “Hongyang” kiwifruit and demonstrated to cause black spot infections on fruits. The genome sequence of Y784-BC03 was obtained using Nanopore MinION technology. The assembled genome is composed of 33,869,130bp (32.30Mb) comprising 10 chromosomes and 11,954 genes. A total of 2,180 virulence factors were predicted to be present in the obtained genome sequence. The virulence factors comprised genes encoding secondary metabolites, including non-host-specific toxins, cell wall-degrading enzymes, and major transcriptional regulators. The predicted gene clusters encoding genes for the biosynthesis and export of secondary metabolites in the genome of Y784-BC03 were associated with non-host-specific toxins, including cercosporin, dothistromin, and versicolorin B. Major transcriptional regulators of different mycotoxin biosynthesis pathways were identified, including the transcriptional regulators, polyketide synthase, P450 monooxygenase, and major facilitator superfamily transporters.

Heteroexpression of Aspergillus nidulans laeA in Marine-Derived Fungi Triggers Upregulation of Secondary Metabolite Biosynthetic Genes

Fungi are a prospective resource of bioactive compounds, but conventional methods of drug discovery are not effective enough to fully explore their metabolic potential. This study aimed to develop an easily attainable method to elicit the metabolic potential of fungi using Aspergillus nidulans laeA as a transcription regulation tool. In this study, functional analysis of Aspergillus nidulans laeA (AnLaeA) and Aspergillus sp. Z5 laeA (Az5LaeA) was done in the fungus Aspergillus sp. Z5. Heterologous AnLaeA-and native Az5LaeA-overexpression exhibited similar phenotypic effects and caused an increase in production of a bioactive compound diorcinol in Aspergillus sp. Z5, which proved the conserved function of this global regulator. In particular, heteroexpression of AnLaeA showed a significant impact on the expression of velvet complex genes, diorcinol synthesis-related genes, and different transcription factors (TFs). Moreover, heteroexpression of AnLaeA influenced the whole genome gene expression of Aspergillus sp. Z5 and triggered the upregulation of many genes. Overall, these findings suggest that heteroexpression of AnLaeA in fungi serves as a simple and easy method to explore their metabolic potential. In relation to this, AnLaeA was overexpressed in the fungus Penicillium sp. LC1-4, which resulted in increased production of quinolactacin A.

Transcriptome analysis on fructose as the sole carbon source enhancing perylenequinones production of endophytic fungus Shiraia sp. Slf14

Perylenequinones (PQ), a class of naturally occurring polypeptides, are widely used as a clinical drug for treating skin diseases and as a photodynamic therapy against cancers and viruses. In this study, the effects of different carbon sources on PQ biosynthesis by Shiraia sp. Slf14 were compared, and the underlying molecular mechanism of fructose as the sole carbon to enhance PQ production was investigated by transcriptome analysis. The results indicated that fructose enhanced PQ yield to 1753.64 mg/L, which was 1.73-fold higher than that obtained with glucose. Comparative transcriptome analysis demonstrated that most of the upregulated genes were related to transport systems, energy and central carbon metabolism in Shiraia sp. Slf14 cultured in fructose. The genes involved in glycolysis and pentose phosphate pathways, and encoding citrate synthase, ATP-citrate lyase, and acetyl-CoA carboxylase were substantially upregulated, resulting in increased overall acetyl-CoA and malonyl-CoA production. However, genes involved in gluconeogenesis, glyoxylate cycle pathway, and fatty acid synthesis were significantly downregulated, resulting in higher acetyl-CoA influx for PQ formation. In particular, the putative PQ biosynthetic cluster was upregulated in Shiraia sp. Slf14 cultured in fructose, leading to a significant increase in PQ production. The results of real-time qRT-PCR and related enzyme activities were also consistent with those of transcriptome analysis. These findings provide a remarkable insight into the underlying mechanism of PQ biosynthesis and pave the way for improvements in PQ production by Shiraia sp. Slf14.

MoLAEA Regulates Secondary Metabolism in Magnaporthe oryzae

Fungi are rich sources of secondary metabolites of pharmaceutical importance, such as antibiotics, antitumor agents, and immunosuppressants, as well as of harmful toxins. Secondary metabolites play important roles in the development and pathogenesis of fungi. LaeA is a global regulator of secondary metabolism and was originally reported in Aspergillus nidulans; however, its role in secondary metabolism in Magnaporthe oryzae has not yet been reported. Here, we investigated the role of a gene homologous to LAEA (loss of AflR expression) of Aspergillus spp. in Magnaporthe oryzae, named M. oryzaeLAEA (MoLAEA). Studies on MoLAEA overexpression and knockdown strains have suggested that this gene acts as a negative regulator of sporulation and melanin synthesis. However, it is not involved in the growth and pathogenesis of M. oryzae Transcriptomic data indicated that MoLAEA regulated genes involved in secondary metabolism. Interestingly, we observed (for the first time, to our knowledge) that this gene is involved in benzylpenicillin (penicillin G) synthesis in M. oryzae Overexpression of MoLAEA increased penicillin G production, whereas the silenced strain showed a complete absence of penicillin G compared to its presence in the wild type. We also observed that MoLaeA interacted with MoVeA, a velvet family protein involved in fungal development and secondary metabolism, in the nucleus. This study showed that though MoLAEA may not make any contribution in rice blast fungal pathogenesis, it regulates secondary metabolism in M. oryzae and thus can be further studied for identifying other new uncharacterized metabolites in this fungus.IMPORTANCEM. oryzae causes blast disease, the most serious disease of cultivated rice affecting global rice production. The genome of M. oryzae has been shown to have a number of genes involved in secondary metabolism, but most of them are uncharacterized. In fact, compared to studies of other filamentous fungi, hardly any work has been done on secondary metabolism in M. oryzae It is shown here (for the first time, to our knowledge) that penicillin G is being synthesized in M. oryzae and that MoLAEA is involved in this process. This is the first step in understanding the penicillin G biosynthesis pathway in M. oryzae This study also unraveled the details of how MoLaeA works by forming a nuclear complex with MoVeA in M. oryzae, thus indicating functional conservation of such a gene across filamentous fungi. All these findings open up avenues for more relevant investigations on the genetic regulation of secondary metabolism in M. oryzae.

DsEcp2-1 is a polymorphic effector that restricts growth of Dothistroma septosporum in pine

The detrimental effect of fungal pathogens on forest trees is an increasingly important problem that has implications for the health of our planet. Despite this, the study of molecular plant-microbe interactions in forest trees is in its infancy, and very little is known about the roles of effector molecules from forest pathogens. Dothistroma septosporum causes a devastating needle blight disease of pines, and intriguingly, is closely related to Cladosporium fulvum, a tomato pathogen in which pioneering effector biology studies have been carried out. Here, we studied D. septosporum effectors that are shared with C. fulvum, by comparing gene sequences from global isolates of D. septosporum and assessing effector function in both host and non-host plants. Many of the effectors were predicted to be non-functional in D. septosporum due to their pseudogenization or low expression in planta, suggesting adaptation to lifestyle and host. Effector sequences were polymorphic among a global collection of D. septosporum isolates, but there was no evidence for positive selection. The DsEcp2-1 effector elicited cell death in the non-host plant Nicotiana tabacum, whilst D. septosporum DsEcp2-1 mutants showed increased colonization of pine needles. Together these results suggest that DsEcp2-1 might be recognized by an immune receptor in both angiosperm and gymnosperm plants. This work may lead to the identification of plant targets for DsEcp2-1 that will provide much needed information on the molecular basis of gymnosperm-pathogen interactions in forests, and may also lead to novel methods of disease control.

Reduced Virulence of an Introduced Forest Pathogen over 50 Years

Pathogen incursions are a major impediment for global forest health. How pathogens and forest trees coexist over time, without pathogens simply killing their long-lived hosts, is a critical but unanswered question. The Dothistroma Needle Blight pathogen Dothistroma septosporum was introduced into New Zealand in the 1960s and remains a low-diversity, asexual population, providing a unique opportunity to analyze the evolution of a forest pathogen. Isolates of D. septosporum collected from commercial pine forests over 50 years were compared at whole-genome and phenotype levels. Limited genome diversity and increased diversification among recent isolates support the premise of a single introduction event. Isolates from the 1960s show significantly elevated virulence against Pinus radiata seedlings and produce higher levels of the virulence factor dothistromin compared to isolates collected in the 1990s and 2000s. However, later isolates have no increased tolerance to copper, used in fungicide treatments of infested forests and traditionally assumed to be a strong selection pressure. The isolated New Zealand population of this forest pathogen therefore appears to have become less virulent over time, likely in part to maintain the viability of its long-lived host. This finding has broad implications for forest health and highlights the benefits of long-term pathogen surveys.

Genomic Mushroom Hunting Decrypts Coprinoferrin, A Siderophore Secondary Metabolite Vital to Fungal Cell Development

LaeA is a positive global regulator of secondary metabolism in Ascomycetes, but its role in Basidiomycetes, including medicinal mushrooms, remains uncharacterized. Here, knockout of laeA in the model mushroom Coprinopsis cinerea unexpectedly upregulated the biosynthesis of a novel siderophore, coprinoferrin. Furthermore, knockout of the nonribosomal peptide synthetase-encoding cpf1 responsible for coprinoferrin biosynthesis resulted in growth defect and loss of fruiting body formation, indicating the complex role that this natural product plays in fungal cell development.

Discovery of Two New Sorbicillinoids by Overexpression of the Global Regulator LaeA in a Marine-Derived Fungus Penicillium dipodomyis YJ-11

Overexpression of the global regulator LaeA in a marine-derived fungal strain of Penicillium dipodomyis YJ-11 induced obvious morphological changes and metabolic variations. Further chemical investigation of the mutant strain afforded a series of sorbicillinoids including two new ones named 10,11-dihydrobislongiquinolide (1) and 10,11,16,17-tetrahydrobislongiquinolide (2), as well as four known analogues, bislongiquinolide (3), 16,17-dihydrobislongiquinolide (4), sohirnone A (5), and 2′,3′-dihydrosorbicillin (6). The results support that the global regulator LaeA is a useful tool in activating silent gene clusters in Penicillium strains to obtain previously undiscovered compounds.

Fungal secondary metabolism: regulation, function and drug discovery

One of the exciting movements in microbial sciences has been a refocusing and revitalization of efforts to mine the fungal secondary metabolome. The magnitude of biosynthetic gene clusters (BGCs) in a single filamentous fungal genome combined with the historic number of sequenced genomes suggests that the secondary metabolite wealth of filamentous fungi is largely untapped. Mining algorithms and scalable expression platforms have greatly expanded access to the chemical repertoire of fungal-derived secondary metabolites. In this Review, I discuss new insights into the transcriptional and epigenetic regulation of BGCs and the ecological roles of fungal secondary metabolites in warfare, defence and development. I also explore avenues for the identification of new fungal metabolites and the challenges in harvesting fungal-derived secondary metabolites.

Evolutionary relics dominate the small number of secondary metabolism genes in the hemibiotrophic fungus Dothistroma septosporum

Fungal secondary metabolites have important functions for the fungi that produce them, such as roles in virulence and competition. The hemibiotrophic pine needle pathogen Dothistroma septosporum has one of the lowest complements of secondary metabolite (SM) backbone genes of plant pathogenic fungi, indicating that this fungus produces a limited range of SMs. Amongst these SMs is dothistromin, a well-characterised polyketide toxin and virulence factor that is required for expansion of disease lesions in Dothistroma needle blight disease. Dothistromin genes are dispersed across six loci on one chromosome, rather than being clustered as for most SM genes. We explored other D. septosporum SM genes to determine if they are associated with gene clusters, and to predict what their likely products and functions might be. Of nine functional SM backbone genes in the D. septosporum genome, only four were expressed under a range of in planta and in culture conditions, one of which was the dothistromin PKS backbone gene. Of the other three expressed genes, gene knockout studies suggested that DsPks1 and DsPks2 are not required for virulence and attempts to determine a functional squalestatin-like SM product for DsPks2 were not successful. However preliminary evidence suggested that DsNps3, the only SM backbone gene to be most highly expressed in the early stage of disease, appears to be a virulence factor. Thus, despite the small number of SM backbone genes in D. septosporum, most of them appear to be poorly expressed or dispensable for virulence in planta. This work contributes to a growing body of evidence that many fungal secondary metabolite gene clusters might be non-functional and may be evolutionary relics.

Global insight into the distribution of velvet-like B protein in Cochliobolus species and implication in pathogenicity and fungicide resistance

The Cochliobolus genus consist of over 55 species among which the 5 most devastating are Cochliobolus carbonum, Cochliobolus heterostrophus, Cochliobolus miyabeanus, Crocus sativus and Cochliobolus lunatus causing damages in sorghum, wheat, rice, maize, cassava and soybean estimated at over 10 billion USD per annum worldwide. The dynamic pathogenicity of Cochliobolus species and the plethora of infected hosts is determined by the evolution of virulence determinants such as the velvet-like B protein (VelB). Nonetheless, the knowledge on the distribution of Cochliobolus VelB and its implication in pathogenicity and fungicide resistance are often lacking. By scanning through the annotated genomes of C. lunatus, C. heterostrophus, C. carbonum, C. victoriae, C. sativus and C. miyabeanus, it is revealed that the numbers of ortholog VelB and cognates vary. By using the phylogenetic approach, it is established that the diversification rates among velvet-domain-containing proteins for phytopathogenic Cochliobolus species could impact differently on their oxidant and fungicide resistance potentials, ability to form appressoria-like structures and infection pegs during infection. This study provides new insights into the pathogenicity evolution of Cochliobolus species at the VelB locus which is relevant for designing effective strategies for durable management of Cochliobolus diseases.

Exploration of the Regulatory Mechanism of Secondary Metabolism by Comparative Transcriptomics in Aspergillus flavus

Mycotoxins cause a huge threaten to agriculture, food safety, and human and animal life. Among them, aflatoxins (AFs) have always been considered the most potent carcinogens, and filamentous fungi from Aspergillus genus are their major producers, especially A. flavus. Although the biosynthesis path of these chemicals had been well-identified, the regulatory mechanisms controlling expression of AF gene cluster were poorly understood. In this report, genome-wide transcriptome profiles of A. flavus from AF conducing [yeast sucrose media (YES)] and non-conducing [yeast peptone media (YEP)] conditions were compared by using deep RNA sequencing (RNA-seq), and the results revealed that AF biosynthesis pathway and biosynthesis of amino acids were significantly upregulated in YES vs. YEP. Further, a novel LaeA-like methyltransferase AFLA_121330 (Lael1) was identified for the first time, to play a specific role in the regulation of AF biosynthesis. Contrary to LaeA, which gene deletion reduced the level, lael1 deletion resulted in a significant increase in AF production. Further, co-expression network analysis revealed that mitochondrial pyruvate transport and signal peptide processing were potentially involved in AF synthesis for the first time, as well as biological processes of ribosome, branched-chain amino acid biosynthetic process and translation were co-regulated by AfRafA and AfStuA. To sum up, our analyses could provide novel insights into the molecular mechanism for controlling the AF and other secondary metabolite synthesis, adding novel targets for plant breeding and making fungicides.

Distinct Roles of Velvet Complex in the Development, Stress Tolerance, and Secondary Metabolism in Pestalotiopsis microspora, a Taxol Producer

The velvet family proteins have been shown to play critical roles in fungal secondary metabolism and development. However, variations of the roles have been observed in different fungi. We report here the observation on the role of three velvet complex components VeA, VelB, and LaeA in Pestalotiopsis microspora, a formerly reported taxol-producing fungus. Deletion of individual members led to the retardation of vegetative growth and sporulation and pigmentation, suggesting critical roles in these processes. The mutant strain △velB appeared hypersensitive to osmotic stress and the dye Congo red, whereas △veA and △laeA were little affected by the pressures, suggesting only velB was required for the integrity of the cell wall. Importantly, we found that the genes played distinct roles in the biosynthesis of secondary metabolites in P. microspora. For instance, the production of pestalotiollide B, a previously characterized polyketide, required velB and laeA. In contrast, the veA gene appeared to inhibit the pestalotiollide B (PB) role in its biosynthesis. This study suggests that the three components of the velvet complex are important global regulators, but with distinct roles in hyphal growth, asexual production, and secondary metabolism in P. microspora. This work provides information for further understanding the biosynthesis of secondary metabolism in the fungus.