Gene cloning, expression, and characterization of trehalose-6-phosphate synthase from Pleurotus ostreatus

Salicylic Acid Treatment Alleviates the Heat Stress Response by Reducing the Intracellular ROS Level and Increasing the Cytosolic Trehalose Content in Pleurotus ostreatus

Pleurotus ostreatus is usually cultivated in horticultural facilities that lack environmental control systems and often suffer heat stress (HS). Salicylic acid (SA) is recognized as a plant defense-related hormone. Here, SA treatment (200 μM) induced fungal resistance to HS of P. ostreatus, with decreased malondialdehyde (MDA) content and HSP expression. Further analysis showed that SA treatment in P. ostreatus increased the cytosolic trehalose content and reduced the intracellular reactive oxygen species (ROS) level. Moreover, H₂O₂ could restore the MDA content and HSP expression of P. ostreatus treated with SA under HS. In addition, trehalose (25 mM) or CaCl₂ (5 mM) treatment induced fungal resistance to HS, and CaCl₂ treatment increased the cytosolic trehalose content of P. ostreatus under HS. However, inhibiting Ca²⁺ levels using Ca²⁺ inhibitors or mutants reversed the trehalose content induced by SA in P. ostreatus under HS. In addition, inhibiting trehalose biosynthesis using Tps-silenced strains reversed the MDA content and HSP expression of P. ostreatus treated with SA under HS. Taken together, these results indicate that SA treatment alleviates the HS response of P. ostreatus by reducing the intracellular ROS level and increasing the cytosolic trehalose content. IMPORTANCE Heat stress (HS) is a crucial environmental challenge for edible fungi. Salicylic acid (SA), a plant defense-related hormone, plays key roles in plant responses to biotic and abiotic stresses. In this study, we found that SA treatment increased the cytosolic trehalose content and induced fungal resistance to HS in P. ostreatus. Further analysis showed that SA can alleviate the HS of P. ostreatus by reducing the intracellular ROS level and increasing the cytosolic trehalose content. Our results help to understand the mechanism underlying the responses of P. ostreatus to HS. In addition, this research provides new insights for the cultivation of P. ostreatus.

Cloning Method for Stress-Resistant Gene of Conringia planisiliqua under Drought Stress

The low temperature, drought, high salt, and other environments influence crop production and development directly, so the gene cloning method has become an effective biological means. In order to effectively improve the cloning effect, a gene cloning method for Conringia planisiliqua based on mRNA differential display technology was proposed. Based on mRNA differential display technology, the gene of Conringia planisiliqua was transcribed. The present study expects gene cloning to be better than the traditional method. This will lay the basis for gene cloning and functional verification of the transcription and disease-resistant proteins in Conringia planisiliqua. According to homologous identification results, the homologous drought-resistant genes were determined and screened. The data of Conringia planisiliqua in the existing biological database were used to extract ESTs data of Conringia planisiliqua. Then, the heating environment was established and the concept of integral function was introduced to express the influence of growth environment of different genomes. The mass, momentum, energy, and turbulent flow situation of stress-resistant gene of Conringia planisiliqua during the growth were satisfied. Finally, the data search was carried out in the NCBI database and gene cloning was achieved by ESTs data sequence. Experimental results show that the proposed method can effectively reduce the gene data fitting and improve the quantity of gene fragments cloned in a cycle, so the overall cloning effect is better.

Comparative Proteomic Analysis of Pleurotus ostreatus Reveals Great Metabolic Differences in the Cap and Stipe Development and the Potential Role of Ca2+ in the Primordium Differentiation

Pleurotus ostreatus is a widely cultivated edible fungus around the world. At present, studies on the developmental process of the fruiting body are limited. In our study, we compared the differentially expressed proteins (DEPs) in the stipe and cap of the fruiting body by high-throughput proteomics. GO and pathway analysis revealed the great differences in the metabolic levels, including sucrose and starch metabolism, and sphingolipid signaling and metabolism, and the differences of 16 important DEPs were validated further by qPCR analysis in expression level. In order to control the cap and stipe development, several chemical inducers were applied to the primordium of the fruiting body according to the pathway enrichment results. We found that CaCl₂ can affect the primordium differentiation through inhibiting the stipe development. EGTA (ethyleneglycol bis (β-aminoethyl ether)-N,N,N′,N′-tetraacetic acid) treatment confirmed the inhibitory role of Ca²⁺ in the stipe development. Our study not only shows great metabolic differences during the cap and stipe development but also reveals the underlying mechanism directing the primordium differentiation in the early development of the fruiting body for the first time. Most importantly, we provide a reliable application strategy for the cultivation and improvement of the Pleurotus ostreatus, which can be an example and reference for a more edible fungus.

Expression patterns of two pal genes of Pleurotus ostreatus across developmental stages and under heat stress

Background

Phenylalanine ammonia-lyase (PAL, EC 4.3.1.24) is the first key enzyme in the phenylpropanoid pathway. The pal gene has been widely studied in plants and participates in plant growth, development and defense systems. However, in Pleurotus ostreatus, the biological functions of pal during organismal development and exposure to abiotic stress have not been reported.

Results

In this study, we cloned and characterized the pal1 (2232 bp) and pal2 (2244 bp) genes from the basidiomycete P. ostreatus CCMSSC 00389. The pal1 and pal2 genes are interrupted by 6 and 10 introns, respectively, and encode proteins of 743 and 747 amino acids, respectively. Furthermore, prokaryotic expression experiments showed that PAL enzymes catalyzed the conversion of L-phenylalanine to trans-cinnamic acid. The function of pal1 and pal2 was determined by constructing overexpression (OE) and RNA interference (RNAi) strains. The results showed that the two pal genes had similar expression patterns during different developmental stages. The expression of pal genes was higher in the reproductive growth stage than in the vegetative growth stage. And the interference of pal1 and pal2 delayed the formation of primordia. The results of heat stress assays showed that the RNAi-pal1 strains had enhanced mycelial tolerance to high temperature, while the RNAi-pal2 strains had enhanced mycelial resistance to H₂O₂.

Conclusions

These results indicate that two pal genes may play a similar role in the development of P. ostreatus fruiting bodies, but may alleviate stress through different regulatory pathways under heat stress.

Trehalose induced by reactive oxygen species relieved the radial growth defects of Pleurotus ostreatus under heat stress

Trehalose is a nonreducing disaccharide, and it plays an intracellular protective role in organisms under various stress conditions. In this study, the trehalose synthesis and its protective role in Pleurotus ostreatus were investigated. As a signal in metabolic regulation, reactive oxygen species (ROS) accumulated in the mycelia of P. ostreatus under heat stress (HS). Furthermore, mycelial growth was significantly inhibited, and the malondialdehyde (MDA) level significantly increased under HS. First, exogenous addition of H₂O₂ inhibited mycelial growth and elevated the MDA level, while N-acetyl cysteine (NAC) and vitamin C (VC) reduced the MDA level and recovered mycelial growth under HS by scavenging ROS. These results indicated that the mycelial radial growth defect under HS might be partly caused by ROS accumulation. Second, adding NAC and VC to the media resulted in rescued trehalose accumulation, which indicated that ROS has an effect on inducing trehalose synthesis. Third, the mycelial growth was recovered by addition of trehalose to the media after HS, and the MDA level was reduced. This effect was further verified by the overexpression of genes for trehalose-6-phosphate synthase (TPS) and neutral trehalase (NTH), which led to increased and reduced trehalose content, respectively. In addition, adding validamycin A (NTH inhibitor) to the media promoted trehalose accumulation and the recovered mycelial growth after HS. In conclusion, trehalose production was partly induced by ROS accumulation in the mycelia under HS, and the accumulated trehalose could promote the recovery of growth after HS, partly by reducing the MDA level in the mycelia.

Genome-Wide Characterization and Expression Analyses of Pleurotus ostreatus MYB Transcription Factors during Developmental Stages and under Heat Stress Based on de novo Sequenced Genome

Pleurotus ostreatus is a commercially grown mushroom species in China. However, studies on the mechanisms of the fruiting body development and stress response of P. ostreatus are still at a primary stage. In this study, we report the entire genome sequence of P. ostreatus CCMSSC03989. Then, we performed comprehensive genome-wide characterization and expression analysis of the MYB transcription factor family during a series of developmental stages and under the condition of heat stress. A 34.76 Mb genome was obtained through next-generation sequencing (NGS) and Bionano optical mapping approaches. The genome has a scaffold N50 of 1.1 Mb and contains 10.11% repeats, and 10,936 gene models were predicted. A total of 20 MYB genes (PoMYB) were identified across the genome, and the full-length open reading frames were isolated. The PoMYBs were classified into 1 repeat (1R), 2R, and 3R-MYB groups according to their MYB domain repeat numbers, and 3R-MYBs possessed relatively more introns than 1R and 2R-MYBs. Based on phylogenetic analysis, the PoMYBs were divided into four groups and showed close relationships with the MYB genes of plants and fungi. RNA-sequencing (RNA-Seq) and quantitative PCR (qPCR) analyses revealed that PoMYB expression showed stage-specific patterns in reproductive stages and could be induced by heat stress. The P. ostreatus draft genome will promote genome-wide analysis, and our study of PoMYBs will promote further functional analysis of MYB genes in mushrooms.

Cloning, purification and characterization of trehalose-6-phosphate synthase from Pleurotus tuoliensis

Pleurotus tuoliensis, a kind of valuable and favorable edible mushroom in China, is always subjected to high environmental temperature during cultivation. In our previous study with P. tuoliensis, trehalose proved to be effective for tolerating heat stress. Trehalose-6-phosphate synthase (TPS; EC2.4.1.15) plays a key role in the biosynthesis of trehalose in fungi. In this study, a full-length of cDNA with 1,665 nucleotides encoding TPS (PtTPS) in P. tuoliensis was cloned. The PtTPS amino acid was aligned with other homologues and several highly conserved regions were analyzed. Thus, the TPS protein was expressed in Escherichia coli and purified by affinity chromatography to test its biochemical properties. The molecular mass of the enzyme is about 60 kDa and the optimum reaction temperature and pH is 30 °C and 7, respectively. The UDP-glucose and glucose-6-phosphate were the optimum substrates among all the tested glucosyl donors and acceptors. Metal cations like Mg²⁺, Co²⁺, Mn²⁺, Ni²⁺, K⁺, Ag⁺ stimulated PtTPS activity significantly. Metal chelators such as sodium citrate, citric acid, EDTA, EGTA and CDTA inhibited enzyme activity. Polyanions like heparin and chondroitin sulfate were shown to stimulate TPS activity.