Genome Sequencing of Cladobotryum protrusum Provides Insights into the Evolution and Pathogenic Mechanisms of the Cobweb Disease Pathogen on Cultivated Mushroom

Genomic insights into the evolution and adaptation of secondary metabolite gene clusters in fungicolous species Cladobotryum mycophilum ATHUM6906

Mycophilic or fungicolous fungi can be found wherever fungi exist since they are able to colonize other fungi, which occupy a diverse range of habitats. Some fungicolous species cause important diseases on Basidiomycetes, and thus, they are the main reason for the destruction of mushroom cultivations. Nonetheless, despite their ecological significance, their genomic data remain limited. Cladobotryum mycophilum is one of the most aggressive species of the genus, destroying the economically important Agaricus bisporus cultivations. The 40.7 Mb whole genome of the Greek isolate ATHUM6906 is assembled in 16 fragments, including the mitochondrial genome and 2 small circular mitochondrial plasmids, in this study. This genome includes a comprehensive set of 12,282 protein coding, 56 rRNA, and 273 tRNA genes. Transposable elements, CAZymes, and pathogenicity related genes were also examined. The genome of C. mycophilum contained a diverse arsenal of genes involved in secondary metabolism, forming 106 biosynthetic gene clusters, which renders this genome as one of the most BGC abundant among fungicolous species. Comparative analyses were performed for genomes of species of the family Hypocreaceae. Some BGCs identified in C. mycophilum genome exhibited similarities to clusters found in the family Hypocreaceae, suggesting vertical heritage. In contrast, certain BGCs showed a scattered distribution among Hypocreaceae species or were solely found in Cladobotryum genomes. This work provides evidence of extensive BGC losses, horizontal gene transfer events, and formation of novel BGCs during evolution, potentially driven by neutral or even positive selection pressures. These events may increase Cladobotryum fitness under various environmental conditions and potentially during host-fungus interaction.

Comparative genomic analysis of pleurotus species reveals insights into the evolution and coniferous utilization of Pleurotus placentodes

Pleurotus placentodes (PPL) and Pleurotus cystidiosus (PCY) are economically valuable species. PPL grows on conifers, while PCY grows on broad-leaved trees. To reveal the genetic mechanism behind PPL's adaptability to conifers, we performed de novo genome sequencing and comparative analysis of PPL and PCY. We determined the size of the genomes for PPL and PCY to be 36.12 and 42.74 Mb, respectively, and found that they contain 10,851 and 15,673 protein-coding genes, accounting for 59.34% and 53.70% of their respective genome sizes. Evolution analysis showed PPL was closely related to P. ostreatus with the divergence time of 62.7 MYA, while PCY was distantly related to other Pleurotus species with the divergence time of 111.7 MYA. Comparative analysis of carbohydrate-active enzymes (CAZYmes) in PPL and PCY showed that the increase number of CAZYmes related to pectin and cellulose degradation (e.g., AA9, PL1) in PPL may be important for the degradation and colonization of conifers. In addition, geraniol degradation and peroxisome pathways identified by comparative genomes should be another factors for PPL's tolerance to conifer substrate. Our research provides valuable genomes for Pleurotus species and sheds light on the genetic mechanism of PPL's conifer adaptability, which could aid in breeding new Pleurotus varieties for coniferous utilization.

Characterization and Genome Analysis of Cladobotryum mycophilum, the Causal Agent of Cobweb Disease of Morchella sextelata in China

Cobweb disease is a fungal disease that can cause serious damage to edible mushrooms worldwide. To investigate cobweb disease in Morchella sextelata in Guizhou Province, China, we isolated and purified the pathogen responsible for the disease. Through morphological and molecular identification and pathogenicity testing on infected M. sextelata, we identified Cladobotryum mycophilum as the cause of cobweb disease in this region. This is the first known occurrence of this pathogen causing cobweb disease in M. sextelata anywhere in the world. We then obtained the genome of C. mycophilum BJWN07 using the HiFi sequencing platform, resulting in a high-quality genome assembly with a size of 38.56 Mb, 10 contigs, and a GC content of 47.84%. We annotated 8428 protein-coding genes in the genome, including many secreted proteins, host interaction-related genes, and carbohydrate-active enzymes (CAZymes) related to the pathogenesis of the disease. Our findings shed new light on the pathogenesis of C. mycophilum and provide a theoretical basis for developing potential prevention and control strategies for cobweb disease.

Draft Genome and Biological Characteristics of Fusarium solani and Fusarium oxysporum Causing Black Rot in Gastrodia elata

Gastrodia elata is a valuable traditional Chinese medicinal plant. However, G. elata crops are affected by major diseases, such as brown rot. Previous studies have shown that brown rot is caused by Fusarium oxysporum and F. solani. To further understand the disease, we studied the biological and genome characteristics of these pathogenic fungi. Here, we found that the optimum growth temperature and pH of F. oxysporum (strain QK8) and F. solani (strain SX13) were 28 °C and pH 7, and 30 °C and pH 9, respectively. An indoor virulence test showed that oxime tebuconazole, tebuconazole, and tetramycin had significant bacteriostatic effects on the two Fusarium species. The genomes of QK8 and SX13 were assembled, and it was found that there was a certain gap in the size of the two fungi. The size of strain QK8 was 51,204,719 bp and that of strain SX13 was 55,171,989 bp. Afterwards, through phylogenetic analysis, it was found that strain QK8 was closely related to F. oxysporum, while strain SX13 was closely related to F. solani. Compared with the published whole-genome data for these two Fusarium strains, the genome information obtained here is more complete; the assembly and splicing reach the chromosome level. The biological characteristics and genomic information we provide here lay the foundation for further research on G. elata brown rot.

Complete Genomic Characterization and Identification of Saccharomycopsisphalluae sp. nov., a Novel Pathogen Causes Yellow Rot Disease on Phallus rubrovolvatus

“Hongtuozhusun” (Phallus rubrovolvatus) is an important edible and medicinal mushroom endemic to Southwest China. However, yellow rot disease is a severe disease of P. rubrovolvatus that occurs extensively in Guizhou Province. It has caused major economic losses and hinders the development of the P. rubrovolvatus industry. In this study, 28 microorganism strains were isolated from diseased fruiting bodies of P. rubrovolvatus at various stages, two of which were confirmed to be pathogenic based on Koch’s postulates. These two strains are introduced herein as Saccharomycopsisphalluae sp. nov. based on morphological, physiological, and molecular analysis. We reported a high-quality de novo sequencing and assembly of the S. phalluae genome using single-molecule real-time sequencing technology. The whole genome was approximately 14.148 Mb with a G+C content of 43.55%. Genome assembly generated 8 contigs with an N50 length of 1,822,654 bp. The genome comprised 5966 annotated protein-coding genes. This is the first report of mushroom disease caused by Saccharomycopsis species. We expect that the information on genome properties, particularly in pathogenicity-related genes, assist in developing effective control measures in order to prevent severe losses and make amendments in management strategies.

De novo genome sequencing of mycoparasite Mycogone perniciosa strain MgR1 sheds new light on its biological complexity

Mycogone perniciosa is a mycoparasite causing Wet Bubble Diseases (WBD) of Agaricus bisporus. In the present study, the whole genome of M. perniciosa strain MgR1 was sequenced using Illumina NextSeq500 platform. This sequencing generated 8.03 Gb of high-quality data and a draft genome of 39 Mb was obtained through a de novo assembly of the high-quality reads. The draft genome resulted into prediction of 9276 genes from the 1597 scaffolds. NCBI-based homology analysis revealed the identification of 8660 genes. Notably, non-redundant protein database analysis of the M. perniciosa strain MgR1 revealed its close relation with the Trichoderma arundinaceum. Moreover, ITS-based phylogenetic analysis showed the highest similarity of M. perniciosa strain MgR1 with Hypomyces perniciosus strain CBS 322.22 and Mycogone perniciosa strain PPRI 5784. Annotation of the 3917 genes of M. perniciosa strain MgR1 grouped in three major categories viz. biological process (2583 genes), cellular component (2013 genes), and molecular function (2919 genes). UniGene analysis identified 2967 unique genes in M. perniciosa strain MgR1. In addition, prediction of the secretory and pathogenicity-related genes based on the fungal database indicates that 1512 genes (16% of predicted genes) encode for secretory proteins. Moreover, out of 9276 genes, 1296 genes were identified as pathogenesis-related proteins matching with 51 fungal and bacterial genera. Overall, the key pathogenic genes such as lysine M protein domain genes, G protein, hydrophobins, and cytochrome P450 were also observed. The draft genome of MgR1 provides an understanding of pathogenesis of WBD in A. bisporus and could be utilized to develop novel management strategies.

Research Progress on Phytopathogenic Fungi and Their Role as Biocontrol Agents

Phytopathogenic fungi decrease crop yield and quality and cause huge losses in agricultural production. To prevent the occurrence of crop diseases and insect pests, farmers have to use many synthetic chemical pesticides. The extensive use of these pesticides has resulted in a series of environmental and ecological problems, such as the increase in resistant weed populations, soil compaction, and water pollution, which seriously affect the sustainable development of agriculture. This review discusses the main advances in research on plant-pathogenic fungi in terms of their pathogenic factors such as cell wall-degrading enzymes, toxins, growth regulators, effector proteins, and fungal viruses, as well as their application as biocontrol agents for plant pests, diseases, and weeds. Finally, further studies on plant-pathogenic fungal resources with better biocontrol effects can help find new beneficial microbial resources that can control diseases.

Control of Fungal Diseases in Mushroom Crops while Dealing with Fungicide Resistance: A Review

Mycoparasites cause heavy losses in commercial mushroom farms worldwide. The negative impact of fungal diseases such as dry bubble (Lecanicillium fungicola), cobweb (Cladobotryum spp.), wet bubble (Mycogone perniciosa), and green mold (Trichoderma spp.) constrains yield and harvest quality while reducing the cropping surface or damaging basidiomes. Currently, in order to fight fungal diseases, preventive measurements consist of applying intensive cleaning during cropping and by the end of the crop cycle, together with the application of selective active substances with proved fungicidal action. Notwithstanding the foregoing, the redundant application of the same fungicides has been conducted to the occurrence of resistant strains, hence, reviewing reported evidence of resistance occurrence and introducing unconventional treatments is worthy to pave the way towards the design of integrated disease management (IDM) programs. This work reviews aspects concerning chemical control, reduced sensitivity to fungicides, and additional control methods, including genomic resources for data mining, to cope with mycoparasites in the mushroom industry.

SMARTdenovo: a de novo assembler using long noisy reads

Long-read single-molecule sequencing has revolutionized de novo genome assembly and enabled the automated reconstruction of reference-quality genomes. It has also been widely used to study structural variants, phase haplotypes and more. Here, we introduce the assembler SMARTdenovo, a single-molecule sequencing (SMS) assembler that follows the overlap-layout-consensus (OLC) paradigm. SMARTdenovo (RRID: SCR_017622) was designed to be a rapid assembler, which, unlike contemporaneous SMS assemblers, does not require highly accurate raw reads for error correction. It has performed well in the evaluation of congeneric assemblers and has been successfully users for various assembly projects. It is compatible with Canu for assembling high-quality genomes, and several of the assembly strategies in this program have been incorporated into subsequent popular assemblers. The assembler has been in use since 2015; here we provide information on the development of SMARTdenovo and how to implement its algorithms into current projects.

Genomics and lipidomics analysis of the biotechnologically important oleaginous red yeast Rhodotorula glutinis ZHK provides new insights into its lipid and carotenoid metabolism

Background

Rhodotorula glutinis is recognized as a biotechnologically important oleaginous red yeast, which synthesizes numerous meritorious compounds with wide industrial usages. One of the most notable properties of R. glutinis is the formation of intracellular lipid droplets full of carotenoids. However, the basic genomic features that underlie the biosynthesis of these valuable compounds in R. glutinis have not been fully documented. To reveal the biotechnological potential of R. glutinis, the genomics and lipidomics analysis was performed through the Next-Generation Sequencing and HPLC-MS-based metabolomics technologies.

Results

Here, we firstly assemble the genome of R. glutinis ZHK into 21.8 Mb, containing 30 scaffolds and 6774 predicted genes with a N50 length of 14, 66,672 bp and GC content of 67.8%. Genome completeness assessment (BUSCO alignment: 95.3%) indicated the genome assembly with a high-quality features. According to the functional annotation of the genome, we predicted several key genes involved in lipids and carotenoids metabolism as well as certain industrial enzymes biosynthesis. Comparative genomics results suggested that most of orthologous genes have underwent the strong purifying selection within the five Rhodotorula species, especially genes responsible for carotenoids biosynthesis. Furthermore, a total of 982 lipids were identified using the lipidomics approaches, mainly including triacylglycerols, diacylglyceryltrimethylhomo-ser and phosphatidylethanolamine.

Conclusion

Using whole genome shotgun sequencing, we comprehensively analyzed the genome of R. glutinis and predicted several key genes involved in lipids and carotenoids metabolism. By performing comparative genomic analysis, we show that most of the ortholog genes have undergone strong purifying selection within the five Rhodotorula species. Furthermore, we identified 982 lipid species using lipidomic approaches. These results provided valuable resources to further advance biotechnological applications of R .glutinis.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-020-07244-z.

Genome Sequencing of Paecilomyces Penicillatus Provides Insights into Its Phylogenetic Placement and Mycoparasitism Mechanisms on Morel Mushrooms

Morels (Morchella spp.) are popular edible fungi with significant economic and scientific value. However, white mold disease, caused by Paecilomyces penicillatus, can reduce morel yield by up to 80% in the main cultivation area in China. Paecilomyces is a polyphyletic genus and the exact phylogenetic placement of P. penicillatus is currently still unclear. Here, we obtained the first high-quality genome sequence of P. penicillatus generated through the single-molecule real-time (SMRT) sequencing platform. The assembled draft genome of P. penicillatus was 40.2 Mb, had an N50 value of 2.6 Mb and encoded 9454 genes. Phylogenetic analysis of single-copy orthologous genes revealed that P. penicillatus is in Hypocreales and closely related to Hypocreaceae, which includes several genera exhibiting a mycoparasitic lifestyle. CAZymes analysis demonstrated that P. penicillatus encodes a large number of fungal cell wall degradation enzymes. We identified many gene clusters involved in the production of secondary metabolites known to exhibit antifungal, antibacterial, or insecticidal activities. We further demonstrated through dual culture assays that P. penicillatus secretes certain soluble compounds that are inhibitory to the mycelial growth of Morchella sextelata. This study provides insights into the correct phylogenetic placement of P. penicillatus and the molecular mechanisms that underlie P. penicillatus pathogenesis.

The complete mitochondrial genome of Cladobotryum mycophilum (Hypocreales: Sordariomycetes)

Cladobotryum mycophilum is the causal agent of cobweb disease in many important mushroom crops. In this study, we report the complete mitochondrial genome of C. mycophilum for the first time. The genome is 78,729 bp long and comprises 52 protein-coding genes (PCGs), 2 ribosomal RNA genes (rRNA), and 26 transfer RNA (tRNA) genes. The nucleotide composition of C. mycophilum mitochondrial genome is as follows: A (38.06%), T (34.68%), C (12.19%), and G (15.07%). Phylogenetic analysis revealed that C. mycophilum had a close relationship with Cladobotryum varium from Hypocreaceae. This study provided a basis for studies of the mitochondrial evolution of Hypocreaceae.

Genomic Features of Cladobotryum dendroides, Which Causes Cobweb Disease in Edible Mushrooms, and Identification of Genes Related to Pathogenicity and Mycoparasitism

Cladobotryum dendroides, which causes cobweb disease in edible mushrooms, is one of the major fungal pathogens. Our previous studies focused on the genetic and morphological characterization of this fungus, as well as its pathogenicity and the identification of appropriate fungicides. However, little is known about the genome characters, pathogenic genes, and molecular pathogenic mechanisms of C. dendroides. Herein, we reported a high-quality de novo genomic sequence of C. dendroides and compared it with closely-related fungi. The assembled C. dendroides genome was 36.69 Mb, consisting of eight contigs, with an N50 of 4.76 Mb. This genome was similar in size to that of C. protrusum, and shared highly conserved syntenic blocks and a few inversions with C. protrusum. Phylogenetic analysis revealed that, within the Hypocreaceae, Cladobotryum was closer to Mycogone than to Trichoderma, which is consistent with phenotypic evidence. A significant number of the predicted expanded gene families were strongly associated with pathogenicity, virulence, and adaptation. Our findings will be instrumental for the understanding of fungi-fungi interactions, and for exploring efficient management strategies to control cobweb disease.

Pleurotus eryngii Genomes Reveal Evolution and Adaptation to the Gobi Desert Environment

Pleurotus eryngii (King Oyster) is one of the most highly prized edible mushrooms. Among the diverse varieties within P. eryngii, P. eryngii var. eryngii is the commonest one, with a worldwide distribution, while P. eryngii var. ferulae is only distributed in Europe and China, and is especially adapted to the Gobi Desert in Xinjiang Autonomous Region of China. However, little is known about the genome-wide pattern of evolution and adaptation to the divergent environments of P. eryngii. Here, we present the high-quality genome sequences of P. eryngii var. eryngii strain PEE81 originating from Europe and P. eryngii var. ferulae strain PEF12 originating from the Gobi Desert of China. The assembled genome sizes of PEE81 and PEF12 were 53.6 and 48.0 Mbp, respectively, which are larger than other reported genomes in the genus Pleurotus. We propose that the selective amplification of long terminal repeat (LTR) retrotransposons increases the genome size of the genus Pleurotus, and may play a key role in driving their rapid species diversification. Molecular clock analyses of five Pleurotus species, namely PEE81, PEF12, P. tuoliensis, P. ostreatus and P. cf. floridanus suggest that the divergence estimates of the genus Pleurotus over time scales ranged from ∼4 to ∼38 million years ago (Mya), and PEE81 and PEF12 diverged at ∼13 Mya. The whole genome resequencing of 33 geographically diverse strains of P. eryngii var. eryngii and var. ferulae was then performed and the genome variation among and within these two populations were investigated. Comparative analyses of these two populations detected several candidate genes related to stress responses and DNA repair that are putatively involved in adaptation to the Gobi Desert environment. These findings offer insights into genome evolution of the genus Pleurotus and provide valuable genomic resources for King Oyster mushroom breeding.

Genomic Analyses Reveal Evidence of Independent Evolution, Demographic History, and Extreme Environment Adaptation of Tibetan Plateau Agaricus bisporus

Agaricus bisporus distributed in the Tibetan Plateau of China has high-stress resistance that is valuable for breeding improvements. However, its evolutionary history, specialization, and adaptation to the extreme Tibetan Plateau environment are largely unknown. Here, we performed de novo genome sequencing of a representative Tibetan Plateau wild strain ABM and comparative genomic analysis with the reported European strain H97 and H39. The assembled ABM genome was 30.4 Mb in size, and comprised 8,562 protein-coding genes. The ABM genome shared highly conserved syntenic blocks and a few inversions with H97 and H39. The phylogenetic tree constructed by 1,276 single-copy orthologous genes in nine fungal species showed that the Tibetan Plateau and European A. bisporus diverged ∼5.5 million years ago. Population genomic analysis using genome resequencing of 29 strains revealed that the Tibetan Plateau population underwent significant differentiation from the European and American populations and evolved independently, and the global climate changes critically shaped the demographic history of the Tibetan Plateau population. Moreover, we identified key genes that are related to the cell wall and membrane system, and the development and defense systems regulated A. bisporus adapting to the harsh Tibetan Plateau environment. These findings highlight the value of genomic data in assessing the evolution and adaptation of mushrooms and will enhance future genetic improvements of A. bisporus.

Genome Analysis of Hypomyces perniciosus, the Causal Agent of Wet Bubble Disease of Button Mushroom (Agaricus bisporus)

The mycoparasitic fungus Hypomyces perniciosus causes wet bubble disease of mushrooms, particularly Agaricus bisporus. The genome of a highly virulent strain of H. perniciosus HP10 was sequenced and compared to three other fungi from the order Hypocreales that cause disease on A. bisporus. H. perniciosus genome is ~44 Mb, encodes 10,077 genes and enriched with transposable elements up to 25.3%. Phylogenetic analysis revealed that H. perniciosus is closely related to Cladobotryum protrusum and diverged from their common ancestor ~156.7 million years ago. H. perniciosus has few secreted proteins compared to C. protrusum and Trichoderma virens, but significantly expanded protein families of transporters, protein kinases, CAZymes (GH 18), peptidases, cytochrome P450, and SMs that are essential for mycoparasitism and adaptation to harsh environments. This study provides insights into H. perniciosus evolution and pathogenesis and will contribute to the development of effective disease management strategies to control wet bubble disease.