Physiological Characteristics and Comparative Secretome Analysis of Morchella importuna Grown on Glucose, Rice Straw, Sawdust, Wheat Grain, and MIX Substrates

Comparative secretome analysis of Oudemansiella raphanipes grown on different agricultural residues

Oudemansiella raphanipes can degrade lignocellulose-rich biomass, especially agricultural residues. However, its substrate utilization and degradation mechanisms remain poorly understood. To explore this, we cultured O. raphanipes mycelium in Kirk's liquid medium supplemented with eight distinct substrates and conducted studies on extracellular enzyme activities and secretome analysis. A total of 905 secreted proteins were identified, with the cornstalk group having the highest counts. Carbohydrate-active enzymes (CAZymes) were the predominant type (32.8-48.9 %), followed by oxidoreductases (2.8 %-13.3 %), while lipase and phosphatase were minor categories. Functional annotation of the secreted proteins comprehensively revealed their diversity in various biological processes. Among the 340 secreted proteins with Enzyme Commission codes, (Methyl)glyoxal oxidase, chitinase, and β-glucosidase were most prominent. Bran, cottonseed hulls, corncobs, and the mixture promoted mycelium growth and conserved CAZymes expression patterns. In contrast, sawdust, corn steep liquor, and cornstalk induced divergent secretome profiles. Sawdust led to a higher proportion of hemicellulose- and lignin-degrading enzymes. Corn steep liquor induced relatively high activities and abundances of laccase and MnP, while cornstalk induced a broad spectrum of oxidoreductases, lipases, and protease & peptidases. In addition, redundancy analysis further indicated that the extracellular enzyme activities (notably laccase, MnP, and xylanase) induced by different substrates significantly impacted the secretome. SIGNIFICANCE: O. raphanipes can efficiently utilize a variety of lignocellulosic materials, and genomic sequencing has confirmed the presence of abundant CAZymes in its genome. This study employed various agricultural residues as substrate inducers to elucidate the extracellular enzyme profiles of O. raphanipes involved in lignocellulose degradation, which indicated its metabolic plasticity in response to varying substrate composition. These findings facilitate further exploration of the biomass bioconversion mechanism of O. raphanipes and provide novel perspectives for the induction of combined agro-residues in its industrial cultivation.

Exogenous MnSO4 Improves Productivity of Degenerated Volvariella volvacea by Regulating Antioxidant Activity

Manganese is one of the trace elements necessary for organisms to maintain normal biological activities and is also a cofactor for manganese superoxide dismutase (Mn-SOD) and manganese peroxidase (MnP). In order to find a simple and effective method to rejuvenate the degenerated V. volvacea strains, we explored the effect of the exogenous addition of MnSO4 on the antioxidant vigour and productivity of degenerated strains of V. volvacea. The results showed that the exogenous MnSO4 had no significant effect on the non-degenerated strain T0, but it could effectively increase the mycelial growth rate, mycelial biomass, and LBL decolouring ability of the degenerated strains T10 and T19, and reduce the production cycle and increased the biological efficiency of T10; it helped the severely degenerated T19 to regrow its fruiting body; and it also significantly increased the viability of the matrix-degrading enzymes such as EG, Lac, Xyl, etc. of T10 and T19. Meanwhile, exogenous MnSO4 significantly increased the activity of GPX, GR, CAT, SOD, and the content of GSH, polyphenols, minerals, and polysaccharides in T10 and T19 strains, which resulted in a significant decrease in the accumulation of ROS, such as O2- and H2O2 in T10 and T19. The correlation analysis showed that there was a significant correlation between antioxidant activity and the production ability of V. volvacea. This study can provide theoretical reference and technical support for the rejuvenation research of degenerated strains of V. volvacea and other edible fungi.

Two near-chromosomal-level genomes of globally-distributed Macroascomycete based on single-molecule fluorescence and Hi-C methods

Discinaceae holds significant importance within the Pezizales, representing a prominent group of macroascomycetes distributed globally. However, there is a dearth of genomic studies focusing on this family, resulting in gaps in our understanding of its evolution, development, and ecology. Here we utilized state-of-the-art genome assembly methodologies, incorporating third-generation single-molecule fluorescence and Hi-C-assisted methods, to elucidate the genomic landscapes of Gyromitra esculenta and Paragyromitra xinjiangensis. The genome sizes of two species were determined to be 47.10 Mb and 48.20 Mb, with 23 and 22 scaffolds, respectively. 10,438 and 11,469 coding proteins were identified, with functional annotations encompassing over 96.47% and 94.40%, respectively. Assessment of completeness using BUSCO revealed that 98.71% and 98.89% of the conserved proteins were identified. The application of comparative genomic technology has helped in identifying traits associated with of heterothallic life cycle traits and elucidating unique patterns of chromosomal evolution. Additionally, we identified potential saprotrophic nutritional modes and systematic phylogenetic relationships between the two species. Therefore, this study provides crucial genomic insights into the evolution, nutritional type, and ecological roles of species within the Pezizales.

Integration of Metabolomes and Transcriptomes Provides Insights into Morphogenesis and Maturation in Morchella sextelata

True morels (Morchella, Pezizales) are a popular edible and medicinal fungus with great nutritional and economic value. The dynamics and regulatory mechanisms during the morphogenesis and maturation of morels are poorly understood. In this study, the metabolomes and transcriptomes of the mycelium (MY), primordium differentiation (PR), young fruiting body (YFB), and mature fruiting body (MFB) were comprehensively analyzed to reveal the mechanism of the morphogenesis and maturation of Morchella sextelata. A total of 748 differentially expressed metabolites (DEMs) and 5342 differentially expressed genes (DEGs) were detected, mainly enriched in the carbohydrate, amino acid, and lipid metabolism pathways, with the transition from the mycelium to the primordium being the most drastic stage at both the metabolic and transcriptional levels. The integrated metabolomics and transcriptomics highlighted significant correlations between the DEMs and DEGs, and specific amino acid and nucleotide metabolic pathways were significantly co-enriched, which may play key roles in morphological development and ascocarp maturation. A conceptual model of transcriptional and metabolic regulation was proposed during morphogenesis and maturation in M. sextelata for the first time, in which environmental factors activate the regulation of transcription factors, which then promote metabolic and transcriptional regulation from vegetative to reproductive growth. These results provide insights into the metabolic dynamics and transcriptional regulation during the morphogenesis and maturation of morels and valuable resources for future breeding enhancement and sustainable artificial cultivation.

Large-Scale Field Cultivation of Morchella and Relevance of Basic Knowledge for Its Steady Production

Morels are one of the most highly prized edible and medicinal mushrooms worldwide. Therefore, historically, there has been a large international interest in their cultivation. Numerous ecological, physiological, genetic, taxonomic, and mycochemical studies have been previously developed. At the beginning of this century, China finally achieved artificial cultivation and started a high-scale commercial development in 2012. Due to its international interest, its cultivation scale and area expanded rapidly in this country. However, along with the massive industrial scale, a number of challenges, including the maintenance of steady economic profits, arise. In order to contribute to the solution of these challenges, formal research studying selection, species recognition, strain aging, mating type structure, life cycle, nutrient metabolism, growth and development, and multi-omics has recently been boosted. This paper focuses on discussing current morel cultivation technologies, the industrial status of cultivation in China, and the relevance of basic biological research, including, e.g., the study of strain characteristics, species breeding, mating type structure, and microbial interactions. The main challenges related to the morel cultivation industry on a large scale are also analyzed. It is expected that this review will promote a steady global development of the morel industry based on permanent and robust basic scientific knowledge.

Analysis and modification of central carbon metabolism in Hypsizygus marmoreus for improving mycelial growth performance and fruiting body yield

Hypsizygus marmoreus is one of the main industrially cultivated varieties of edible fungi, with a delicious taste and high nutritional value. However, the long harvest period of 130-150 days greatly limits its large-scale expansion. This study aimed to investigate the effects of central carbon metabolism (CCM) on the mycelial growth performance and fruiting body formation of H. marmoreus. Nine edible fungi with different harvest periods were collected and used to evaluate their intracellular carbon metabolic differences in the CCM, which revealed that the imbalanced distribution of intracellular carbon metabolic levels in the CCM of H. marmoreus might be one of the key factors resulting in a slow mycelial growth rate and a long harvest period. Further analysis by three strategies, including metabolomics, adaptation of different carbon sources, and chemical interference, confirmed that low carbon flux into the pentose phosphate pathway (PPP) limited the supply of raw materials, reduced power, and thus influenced the mycelial growth of H. marmoreus. Furthermore, four transformants with increased expression levels of glucose-6-phosphate dehydrogenase (G6PDH), a key rate-limiting enzyme in the PPP of H. marmoreus, were developed and showed more extracellular soluble protein secretion and higher sugar assimilation rates, as well as improved mycelial growth rates in bottle substrate mixtures. Finally, cultivation experiments indicated that the maturation periods of the fruiting body with ~4-5 days in advance and the maximum fruiting body yield of 574.8 g per bag with an increase of 7.4% were achieved by improving the G6PDH expression level of the PPP in H. marmoreus. This study showed that CCM played an important role in the mycelial growth and development of H. marmoreus, which provided new insights for future advancements in cultivating and breeding edible fungi.

Molecular and cultural characterization of Morchella spp. from disturbed environments of central-southern Chile

In Northwestern Patagonia (Chile), three species of Morchella from undisturbed environments have been identified to date: Morchella tridentina, Morchella andinensis and Morchella aysenina, all belonging to the Elata clade and associated mainly with Nothofagus forests. In this study, the search for Morchella specimens was extended to disturbed environments in Central-Southern Chile, to further explore Morchella species diversity in the country, which is still very limited. The Morchella specimens were identified through multilocus sequences analysis, and the mycelial cultures were characterized, establishing comparisons with specimens from undisturbed environments. To the best of our knowledge, these results reveal for the first time in Chile the presence of the species Morchella eximia and Morchella importuna, and in the case of the last one also the first record in South America. These species were found associated almost exclusively with harvested or burned coniferous plantations. The in vitro mycelial characterization revealed certain inter- and intra-specific patterns of the morphology, such as pigmentation, mycelium type, and development and formation of sclerotia, which varied according to growth media and incubation temperature. The growth rates (mm/day) and mycelial biomass (mg) were significantly influenced by the temperature (p < 0.05), with maximum rates (>10 mm/day) and biomass (approx. 20 mg) between 20 and 24 °C, while a significant growth reduction (70-90%) was observed at 28 °C, mainly in the species from undisturbed environments. Potato-dextrose (PDA) medium stimulated the greatest mycelial density and sclerotia formation in most of the isolates, mainly in M. eximia (UDEC-LAF 236 isolate) which recorded the best mycelial growth performance. Among isolates, UDEC-LAF 236 also showed the best performance in sclerotia production (>350 sclerotia/dish) in 10 days of growth. This study contributes to the knowledge of the diversity of Morchella species in Chile by broadening the species range to those from disturbed environments. It also provides molecular and morphological characterization of the in vitro cultures of different Morchella species. The report on M. eximia and M. importuna, species known as cultivable, adapted to local climatic and edaphic conditions could represent the first step to developing artificial Morchella cultivation methods in Chile.

Activity Assay of Amylase and Xylanase Is Available for Quantitative Assessment of Strain Aging in Cultivated Culinary-Medicinal Morchella Mushrooms (Ascomycotina)

Strain aging has been mainly contributing to the "uncertainty" of Morchella farming. The situation calls for urgent quantitative assessment of strain aging in cultivated Morchella mushrooms. In this paper, systemic senescence of the productive strains of M. eximia, M. importuna, and M. sextelata was achieved through successive subculturing to provide subcultures with different degree of aging for further studies. Then the quantitative assessment of morel strain aging was conducted by activity assay of amylase and xylanase using dinitrosalicylic acid (DNS) method. The results suggested that both activity of amylase and xylanase decreased along with the rise of subculture times. Meanwhile, the correlation between xylanase activity and time of subculturing in the tested morel strains was higher than that of amylase assay. Consequently, assay of amylase and xylanase activity by DNS method can be used in the quantitative assessment of morel strain aging, and assay of xylanase activity is the better alternative. The work will improve the settlement of "uncertainty" in the morel industry and thus be beneficial for stable development of morel farming.

Ultrastructure and Physiological Characterization of Morchella Mitospores and Their Relevance in the Understanding of the Morel Life Cycle

Morels, which belong to the Ascomycete genus Morchella, are highly valued edible fungi treasured by gourmet chefs worldwide. Some species are saprotrophic and others are able to form facultative mycorrhizal-like associations with plant roots without establishing true ectomycorrhizal symbioses. In general, it is considered that the formation of asexual spores, or mitospores, is an important step in the life cycle of morels. However, ultrastructure characterization and physiological attributes of morel mitospores have received little attention. In this contribution, the mitospores of M. sextelata were successfully induced under laboratory conditions and their ultrastructure, occurrence, germination, physiological characteristics and mating type gene structure were studied. Mitospore production was closely related to aeration, nutrition and humidity conditions. The average germination rate of mitospores on different media and under various induction stimuli was very low, with an average of 1/100,000. Based on the ultrastructure characterization, low germination rate, growth rate decline, rapid aging and mating genotyping, it was concluded that the mitospores of M. sextelata had lost their conventional function as conidia and might act more as mate sperm-like (gamete) structures. Thus, this study contributed to a deeper understanding of the life cycle of the economically and ecologically important morel fungal group.

Enzymes and enzymatic mechanisms in enzymatic degradation of lignocellulosic biomass: A mini-review

Enzymatic hydrolysis is the key step limiting the efficiency of the biorefinery of lignocellulosic biomass. Enzymes involved in enzymatic hydrolysis and their interactions with biomass should be comprehended to form the basis for looking for strategies to improve process efficiency. This article updates the contemporary research on the properties of key enzymes in the lignocellulose biorefinery and their interactions with biomass, adsorption, and hydrolysis. The advanced analytical techniques to track the interactions for exploiting mechanisms are discussed. The challenges and prospects for future research are outlined.

Construction of nucleus-directed fluorescent reporter systems and its application to verification of heterokaryon formation in Morchella importuna

INTRODUCTION

Morchella importuna (M. importuna) is a rare fungus with high nutrition value and distinct flavor. Despite the successful artificial cultivation, its genetic characteristics and biological processes such as life cycle, reproductive system, and trophic mode remain poorly understood.

METHODS

Considering this, we constructed pEH2B and pMH2B vectors by fusing M. importuna endogenous histone protein H2B with fluorescent proteins eGFP or mCherry, respectively. Based on the constructed pEH2B and pMH2B vectors, nuclear fluorescence localization was performed via Agrobacterium tumefaciens-mediated transformation (ATMT). These two vectors were both driven by two endogenous promoters glyceraldehyde 3-phosphate dehydrogenase (GPD) and ubiquitin (UBI). The vector-based reporter systems were tested by the paired culture of two genetically modified strains pEH2B-labeled M04M24 (24e, MAT1-1-1) and pMH2B-abeled M04M26 (26m, MAT1-2-1).

RESULTS

The fluorescence observation and molecular identification results indicated the successful hyphal fusion and heterokaryon formation. We found that the expression of the reporter genes was stable, and it did not interfere with the growth of the fungus.

DISCUSSION

Our constructed nucleus-directed fluorescent systems in M. importuna can be used for monitoring the dynamic development and reproductive processes in living cells and also for monitoring the interaction between morels and plant roots. Therefore, morels exhibit the potential to be a candidate organism used for the research on basic biology and genetics of ascomycetes.

Epidemic Identification of Fungal Diseases in Morchella Cultivation across China

True morels (Morchella, Pezizales) are world-renowned edible mushrooms (ascocarps) that are widely demanded in international markets. Morchella has been successfully artificially cultivated since 2012 in China and is rapidly becoming a new edible mushroom industry occupying up to 16,466 hectares in the 2021-2022 season. However, nearly 25% of the total cultivation area has annually suffered from fungal diseases. While a variety of morel pathogenic fungi have been reported their epidemic characteristics are unknown, particularly in regional or national scales. In this paper, ITS amplicon sequencing and microscopic examination were concurrently performed on the morel ascocarp lesions from 32 sites in 18 provinces across China. Results showed that Diploöspora longispora (75.48%), Clonostachys solani (5.04%), Mortierella gamsii (0.83%), Mortierella amoeboidea (0.37%) and Penicillium kongii (0.15%) were the putative pathogenic fungi. The long, oval, septate conidia of D. longispora was observed on all ascocarps. Oval asexual spores and sporogenic structures, such as those of Clonostachys, were also detected in C. solani infected samples with high ITS read abundance. Seven isolates of D. longispora were isolated from seven selected ascocarps lesions. The microscopic characteristics of pure cultures of these isolates were consistent with the morphological characteristics of ascocarps lesions. Diploöspora longispora had the highest amplification abundance in 93.75% of the samples, while C. solani had the highest amplification abundance in six biological samples (6.25%) of the remaining two sampling sites. The results demonstrate that D. longispora is a major culprit of morel fungal diseases. Other low-abundance non-host fungi appear to be saprophytic fungi infecting after D. longispora. This study provides data supporting the morphological and molecular identification and prevention of fungal diseases of morel ascocarps.

Contemporary proteomic research on lignocellulosic enzymes and enzymolysis: A review

This review overviewed the current researches on the isolation of novel strains, the development of novel identification protocols, the key enzymes and their synergistic interactions with other functional enzyme systems, and the strategies for enhancing enzymolysis efficiencies. The main obstacle for realizing biorefinery of lignocellulosic biomass to biofuels or biochemicals is the high cost of enzymolysis stage. Therefore, research prospects to reduce the costs for lignocellulose hydrolysis were outlined.