Stimulative effects of light and a temperature downshift on transcriptional expressions of developmentally regulated genes in the initial stages of fruiting-body formation of the basidiomycetous mushroomLentinula edodes

Low temperature, mechanical wound, and exogenous salicylic acid (SA) can stimulate the SA signaling molecule as well as its downstream pathway and the formation of fruiting bodies in Flammulina filiformis

Low temperature (LT) and mechanical wound (MW), as two common physics methods, have been empirically used in production to stimulate the primordia formation of Flammulina filiformis, which is typically produced using the industrial production mode. However, the detailed effect on the fruiting body formation and important endogenous hormones and signaling pathways in this process is poorly understood. In this study, LT, MW, their combination, i.e., MW + LT, and low concentration of SA (0.1 mM SA) treatments were applied to the physiologically mature mycelia of F. filiformis. The results showed that the primordia under the four treatments began to appear on the 5th-6th days compared with the 12th day in the control (no treatment). The MW + LT treatment produced the largest number of primordia (1,859 per bottle), followed by MW (757), SA (141), and LT (22), compared with 47 per bottle in the control. The HPLC results showed that the average contents of endogenous SA were significantly increased by 1.3 to 2.6 times under four treatments. A total of 11 SA signaling genes were identified in the F. filiformis genome, including 4 NPR genes (FfNpr1-4), 5 TGA genes (FfTga1-5), and 2 PR genes (FfPr1-2). FfNpr3 with complete conserved domains (ANK and BTB/POZ) showed significantly upregulated expression under all four above treatments, while FfNpr1/2/4 with one domain showed significantly upregulated response expression under the partial treatment of all four treatments. FfTga1-5 and FfPr1-2 showed 1.6-fold to 8.5-fold significant upregulation with varying degrees in response to four treatments. The results suggested that there was a correlation between "low temperature/mechanical wound-SA signal-fruiting body formation", and it will help researchers to understand the role of SA hormone and SA signaling pathway genes in the formation of fruiting bodies in fungi.

Multi-Omics Analysis of Low-Temperature Fruiting Highlights the Promising Cultivation Application of the Nutrients Accumulation in Hypsizygus marmoreus

Hypsizygus marmoreus is a representative edible mushroom with low-temperature fruiting after a long postripening (LFLP). Clarifying the mechanism of LFLP and applying a rigorous low-temperature-limited process will optimize the mushroom cultivation process. This study performed an integrative multi-omics analysis of the molecular mechanism of LFLP in combination with genetic, physiological, and cultivation confirmation. The results showed that the amino acid content was increased during LFLP, mainly arginine. pH analysis showed acidification in the postripening stage and alkalization in the substrates of the reproductive growth stage. An enzyme activity test confirmed the increased enzyme activity of arginase and citrate synthase in the postripening stage. Weighted gene coexpression network analysis of the transcriptome and metabolomics indicated that pH variation is correlated mainly with changes in citrate and arginine. Multi-omics reveals a straightforward way of providing enriched materials for amino acid biosynthesis, namely, synergistically elevating citric acid and arginine through enhanced activity of the arginine synthesis branch pathway in the citrate cycle. Our study confirmed that GCN2 mediated metabolic adaptation by enhancing protein translation, highlighting its regulatory role during LFLP. Exogenously added citric acid and arginine shortened the postripening period by 10 days and increased the fruiting body yield by 10.2~15.5%. This research sheds light on the molecular mechanism of LFLP in H. marmoreus and highlights the promising application of nutrient accumulation in high-efficiency cultivation.

Transcriptome and Differentially Expressed Gene Profiles in Mycelium, Primordium and Fruiting Body Development in Stropharia rugosoannulata

Stropharia rugosoannulata uses straw as a growth substrate during artificial cultivation and has been widely promoted in China. However, its fruiting body formation and development processes have not been elucidated. In this study, the developmental transcriptomes were analyzed at three stages: the mycelium (G-S), primordium (P-S) and fruiting body (M-F) stages. A total of 9690 differentially expressed genes (DEGs) were identified in the different developmental stages. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses showed that these DEGs were involved mainly in hydrolase activity, structural molecule activity and oxidoreductase activity as well as xenobiotic biodegradation and metabolism and energy metabolism pathways. We further found that the higher expression of most carbohydrate enzyme (i.e., GH, CE, CBM, AA and PL) genes in the hyphal (i.e., G-S) stage was related mainly to substrate degradation, while the upregulation of glycosyltransferase (GT) gene expression in the P-S and M-F stages may be related to cell wall synthesis. In addition, we found that CO₂-sensing-related genes (i.e., CA-2, CA-3, PKA-1 and PKA-2) were upregulated in the P-S and M-F stages, heat shock protein genes (HSP60 and HSP90) were significantly downregulated in the P-S stage and upregulated in the M-F stage and the transcription factors (i.e., steA, MYB, nosA, HAP1, and GATA-4/5/6) involved in growth and development were significantly upregulated in the P-S stage. These results suggest that environmental factors (i.e., CO₂ and temperature) and transcription factors may play a key role in primordium formation. In short, this study provides new insights into the study of stimulating primordia formation affecting the development of fruiting bodies of S. rugosoannulata.

Transcriptomic analysis of Stropharia rugosoannulata reveals carbohydrate metabolism and cold resistance mechanisms under low-temperature stress

Low temperature is an important environmental factor that restricts the growth of Stropharia rugosoannulata; however, the molecular mechanisms underlying S. rugosoannulata responses to low-temperature stress are largely unknown. In this study, we performed a transcriptome analysis of a high-sensitivity strain (DQ-1) and low-sensitivity strain (DQ-3) under low-temperature stress. The liquid hyphae of S. rugosoannulata treated at 25 °C and 10 °C were analyzed by RNA-Seq, and a total of 9499 differentially expressed genes (DEGs) were identified. GO and KEGG enrichment analyses showed that these genes were enriched in "xenobiotic biodegradation and metabolism", "carbohydrate metabolism", "lipid metabolism" and "oxidoreductase activity". Further research found that carbohydrate enzyme (AA, GH, CE, and GT) genes were downregulated more significantly in DQ-1 than DQ-3 and several cellulase activities were also reduced to a greater extent. Moreover, the CAT1, CAT2, GR, and POD genes and more heat shock protein genes (HSP20, HSP78 and sHSP) were upregulated in the two strains after low-temperature stress, and the GPX gene and more heat shock protein genes were upregulated in DQ-3. In addition, the enzyme activity and qRT-PCR results showed trends similar to those of the RNA-Seq results. This result indicates that low-temperature stress reduces the expression of different AA, GH, CE, and GT enzyme genes and reduces the secretion of cellulase, thereby reducing the carbohydrate metabolism process and mycelial growth of S. rugosoannulata. Moreover, the expression levels of different types of antioxidant enzymes and heat shock proteins are also crucial for S. rugosoannulata to resist low-temperature stress. In short, this study will provide a basis for further research on important signaling pathways, gene functions and variety breeding of S. rugosoannulata related to low-temperature stress.

Transcriptome analysis of the edible mushroom Lentinula edodes in response to blue light

Lentinula edodes is one of the most popular edible mushrooms worldwide and contains important medicinal components such as lentinan, ergosterol, and eritadenine. Mushroom metabolism is regulated by the mycelia and fruit body using light; however, in mushrooms, the underlying molecular mechanisms controlling this process as well as light-induced gene expression remain unclear. Therefore, in this study, we compared morphological changes and gene expression in the fruit bodies of L. edodes cultivated under blue light and continuous darkness. Our results showed that blue light primarily induced pileus growth (diameter and thickness) compared to dark cultivation. Alternatively, stipe length development was promoted by dark cultivation. We also performed RNAseq on L. edodes under the blue light/dark cultivation conditions. A total of 12,051 genes were used for aligning the Illumina raw reads and 762 genes that showed fold change cut-offs of >|2| and significance p-values of <0.05 were selected under blue light condition. Among the genes which showed two-fold changed genes, 221 were upregulated and 541 were downregulated. In order to identify blue light induced candidate genes, differentially expressed genes (DEGs) were selected according to 4-fold changes and validated by RT-PCR. We identified 8 upregulated genes under blue light condition, such as DDR48-heat shock protein, Fasciclin-domain-containing protein and carbohydrate esterase family 4 protein, FAD NAD-binding domain-containing protein that are involved in morphological development of primordium and embryonic muscle development, cell adhesion and affect the structure of cellulosic and non-cellulosic cell walls of fruit body development, and photoreceptor of blue light signaling for fruit body and pigment development, respectively. This study provides valuable insights into the molecular mechanisms underlying the role of blue light in mushroom growth and development and can thus contribute to breeding programs to improve mushroom cultivation.

Blue light exposure and nutrient conditions influence the expression of genes involved in simultaneous hyphal knot formation in Coprinopsis cinerea

Light and nutrients are crucial environmental factors influencing fungal sexual reproduction. Blue light induces simultaneous hyphal knot formation in Coprinopsis cinerea mycelia grown on low-glucose media but not in mycelia grown on high-glucose media. Many hyphal knots are visible in the arc near the edge of the colony one day after 15 min of blue light stimulation. These findings collectively suggest that blue light accelerates hyphal knot induction in nutrient-limited conditions. Transcriptome analysis revealed that gene expression after light exposure is divided into at least two major stages. In the first stage, genes coding for fasciclin (fas1), cyclopropane-fatty-acyl-phospholipid synthases (cfs1 and cfs2), and putative lipid exporter (nod1) are highly expressed after 1 h of light exposure in the mycelial region where the hyphal knot will be developed. These genes are upregulated by blue light and not influenced by glucose condition and mating. These results suggest that although some of the genes are critical for induction of the hyphal knots, they are not sufficient for hyphal knot development. In the second gene expression stage, genes encoding galectins (cgl1-3), farnesyl cysteine-carboxyl methyltransferases, mating pheromone-containing protein, nucleus protein (ich1), and laccase (lcc1) are specifically upregulated at 10-16 h after blue light exposure when the mycelia are cultivated on low-glucose media. These genes might be involved in the architecture of hyphal knots or signal transduction for further fruiting body development. These results contribute to the understanding of the effect of environmental factors on sexual reproduction in basidiomycetous fungi.

Identification of two mutations that cause defects in the ligninolytic system through an efficient forward genetics in the white-rot agaricomycete Pleurotus ostreatus

White-rot fungi play an important role in the global carbon cycle because they are the species that almost exclusively biodegrade wood lignin in nature. Lignin peroxidases (LiPs), manganese peroxidases (MnPs) and versatile peroxidases (VPs) are considered key players in the ligninolytic system. Apart from LiPs, MnPs and VPs, however, only few other factors involved in the ligninolytic system have been investigated using molecular genetics, implying the existence of unidentified elements. By combining classical genetic techniques with next-generation sequencing technology, they successfully showed an efficient forward genetics approach to identify mutations causing defects in the ligninolytic system of the white-rot fungus Pleurotus ostreatus. In this study, they identified two genes - chd1 and wtr1 - mutations in which cause an almost complete loss of Mn²⁺ -dependent peroxidase activity. The chd1 gene encodes a putative chromatin modifier, and wtr1 encodes an agaricomycete-specific protein with a putative DNA-binding domain. The chd1-1 mutation and targeted disruption of wtr1 hamper the ability of P. ostreatus to biodegrade wood lignin. Examination of the effects of the aforementioned mutation and disruption on the expression of certain MnP/VP genes suggests that a complex mechanism underlies the ligninolytic system in P. ostreatus.

Environmental regulation of reproductive phase change in Agaricus bisporus by 1-octen-3-ol, temperature and CO₂

Reproductive phase change from vegetative mycelium to the initiation of fruiting in Agaricus bisporus is regulated in large part by the sensing of environmental conditions. A model is proposed in which three separate environmental factors exert control at different stages of the reproductive developmental process change. The eight carbon volatile 1-octen-3-ol controls the early differentiation from vegetative hyphae to multicellular knots; temperature reduction is essential for the later differentiation of primodia; and carbon dioxide level exerts quantitative control on the number of fruiting bodies developed. Analysis of transcriptomic changes during the reproductive phase change was carried out with initiation-specific microarrays, and the newly published A. bisporus genome was used to analyse the promoter regions of differentially regulated genes. Our studies have shown there to be both early and late initiation responses relating to sensing of eight carbon volatiles and temperature respectively. A subset of 45 genes was transcriptionally regulated during the reproductive phase change which exhibited a range of functions including cell structure, nitrogen and carbon metabolism, and sensing and signalling. Three gene clusters linking increased transcription with developmental stage were identified. Analysis of promoter regions revealed cluster-specific conserved motifs indicative of co-ordinated regulation of transcription.

Efficient gene targeting in ΔCc.ku70 or ΔCc.lig4 mutants of the agaricomycete Coprinopsis cinerea

Coprinopsis cinerea is a model for studies of sexual development in agaricomycetes (homobasidiomycetes). Efficient gene targeting should facilitate such studies, especially because increasing genome and transcriptome information is now available in C. cinerea. To estimate the frequency of gene disruption by homologous integration in this fungus, we tried to disrupt Cc.wc-2, which encodes a WC-2 homolog, a partner of the fungal blue-light photoreceptor, WC-1. Disruption of Cc.wc-2 did not occur when recipients (protoplasts) of the disrupting construct were prepared from asexual spores, oidia, from the wild type, 326, while it occurred when protoplasts were prepared from mycelial cells from the same strain, albeit at a low frequency (3%). Double-stranded RNA-mediated silencing of a ku70 homolog, named Cc.ku70, or the lig4 homolog Cc.lig4 more or less increased the frequency of Cc.wc-2 targeting. On the basis of these results, we disrupted Cc.ku70 using a Cc.lig4-silenced strain. We then disrupted Cc.lig4 using the Cc.ku70 disruptant. We found that the disruption of Cc.ku70 or Cc.lig4 greatly enhanced gene targeting. In addition, this study demonstrates that Cc.wc-2 is involved in blue light perception in this fungus.

Opposing developmental functions of Agrocybe aegerita galectin (AAL) during mycelia differentiation

Mycelia of basidiomycetes differentiating into fruiting body is a controlled developmental process, however the underlying molecular mechanism remains unknown. In previous work, a novel fungal Agrocybe aegerita galectin (AAL) was isolated from A. aegerita in our laboratory. AAL was shown to promote mycelial differentiation in A. aegerita and Auricularia polytricha, indicating that AAL might function as a conserved fruiting initiator during basidiomycete mycelia development. In the current work, we investigate the role of AAL in mycelia differentiation and fruiting body formation. First, the expression and localization of AAL in mycelia, primordium and fruiting body were assessed by Western blotting and immunohistochemistry. AAL was found to be ubiquitously expressed in the primordium and fruiting body but not in the mycelia. AAL facilitated mycelia congregation and promoted fruiting body production when AAL was applied on mycelia. At the same time, when AAL was spread on potato dextrose agar (PDA) medium prior to mycelia inoculation, mycelia exhibited slowed growth rates, resulting in mycelia cords formation and inhibition of fruiting body formation. The 5' regulatory sequence of aal was cloned by 'genome walking'. Here, we show that aal lack introns in the coding region and the upstream 740 bp sequence was characterized by the existence of core promoter elements, which included: two CCAAT boxes (-535/-280), a GC box (-145), a TATA box (-30) and a fungal leader intron within the 5' UTR. The identification of regulatory expression elements may provide an explanation to the stage-specific and high-level expression of aal during fruiting development.