Accumulation of serine proteinase in senescent sporophores of the cultivated mushroom, Agaricus bisporus

Methyl jasmonate differentially and tissue-specifically regulated the expression of arginine catabolism-related genes and proteins in Agaricus bisporus mushrooms during storage

Methyl jasmonate (MeJA)-regulated postharvest quality retention of Agaricus bisporus fruiting bodies is associated with arginine catabolism. However, the mechanism of MeJA-regulated arginine catabolism in edible mushrooms is still unclear. This study aimed to investigate the regulatory modes of MeJA on the expression of arginine catabolism-related genes and proteins in intact and different tissues of A. bisporus mushrooms during storage. Results showed that exogenous MeJA treatment activated endogenous JA biosynthesis in A. bisporus mushrooms, and differentially and tissue-specifically regulated the expression of arginine catabolism-related genes (AbARG, AbODC, AbSPE-SDH, AbSPDS, AbSAMDC, and AbASL) and proteins (AbARG, AbSPE-SDH, AbASL, and AbASS). MeJA caused no significant change in AbASS expression but resulted in a dramatic increase in AbASS protein level. Neither the expression of the AbSAMS gene nor the AbSAMS protein was conspicuously altered upon MeJA treatment. Additionally, MeJA reduced the contents of arginine and ornithine and induced the accumulation of free putrescine and spermidine, which was closely correlated with MeJA-regulated arginine catabolism-related genes and proteins. Hence, the results suggested that the differential and tissue-specific regulation of arginine catabolism-related genes and proteins by MeJA contributed to their selective involvement in the postharvest continuing development and quality retention of button mushrooms.

Preparation and characterization of a novel intelligent starch/gelatin binary film containing purple sweet potato anthocyanins for Flammulina velutipes mushroom freshness monitoring

In this study, intelligent food package was developed and characterized by loading purple sweet potato polyphenolic extract (SPS) into starch/gelatin film. The application of this film in indicating the freshness of Flammulina velutipes was also determined. The color of SPS buffer changed from red to blue and final yellow when pH increasing from 3 to 10. The blending film with starch/gelatin ratio of 1:1 wt showed a minimum water vapor permeability of 6.26 × 10-11 gs-1 m-1 Pa-1. The value of elongation at break and tensile strength of the starch/gelatin film with starch/gelatin ratio of 1:1 wt increased to 78.89 % and 11.70 MPa. Upon its application to monitor of F. velutipes freshness level, SG11 film color changed from initially green to purplish gray and finally to yellow as F. velutipes deteriorated post storage. Our results suggested that SG11 films could be used as an intelligent packaging material in the future for other food products.

Cycling in degradation of organic polymers and uptake of nutrients by a litter-degrading fungus

Wood and litter degrading fungi are the main decomposers of lignocellulose and thus play a key role in carbon cycling in nature. Here, we provide evidence for a novel lignocellulose degradation strategy employed by the litter degrading fungus Agaricus bisporus (known as the white button mushroom). Fusion of hyphae allows this fungus to synchronize the activity of its mycelium over large distances (50 cm). The synchronized activity has a 13-h interval that increases to 20 h before becoming irregular and it is associated with a 3.5-fold increase in respiration, while compost temperature increases up to 2°C. Transcriptomic analysis of this burst-like phenomenon supports a cyclic degradation of lignin, deconstruction of (hemi-) cellulose and microbial cell wall polymers, and uptake of degradation products during vegetative growth of A. bisporus. Cycling in expression of the ligninolytic system, of enzymes involved in saccharification, and of proteins involved in nutrient uptake is proposed to provide an efficient way for degradation of substrates such as litter.

Postharvest biochemical characteristics and ultrastructure of Coprinus comatus

BACKGROUND

Coprinus comatus is a novel cultivated edible fungus, hailed as a new preeminent breed of mushroom. However, C. comatus is difficult to keep fresh at room temperature after harvest due to high respiration, browning, self-dissolve and lack of physical protection.

METHODS

In order to extend the shelf life of C. comatus and reduce its loss in storage, changes in quality, biochemical content, cell wall metabolism and ultrastructure of C. comatus (C.c77) under 4 °C and 90% RH storage regimes were investigated in this study.

RESULTS

The results showed that: (1) After 10 days of storage, mushrooms appeared acutely browning, cap opening and flowing black juice, rendering the mushrooms commercially unacceptable. (2) The activity of SOD, CAT, POD gradually increased, peaked at the day 10, up to 31.62 U g-1 FW, 16.51 U g-1 FW, 0.33 U g-1 FW, respectively. High SOD, CAT, POD activity could be beneficial in protecting cells from ROS-induced injuries, alleviating lipid peroxidation and stabilizing membrane integrity. (3) The activities of chitinase, β-1,3-glucanase were significantly increased. Higher degrees of cell wall degradation observed during storage might be due to those enzymes' high activities. (4) The fresh C. comatus had dense tissue and every single cell had the number of intracellular organelles which structure can be observed clearly. After 10 d storage, the number of intracellular organelles was declined and the structure was fuzzy, the nucleus disappeared. After 20 d storage, C. comatus's organization was completely lost, many cells were stacked together and the cell wall was badly damaged.

Ornithine decarboxylase is involved in methyl jasmonate-regulated postharvest quality retention in button mushrooms (Agaricus bisporus)

BACKGROUND

In the present study, we investigated the role of ornithine decarboxylase (ODC) in the methyl jasmonate (MeJA)-regulated postharvest quality maintenance of Agaricus bisporus (J. E. Kange) Imbach button mushrooms by pretreating mushrooms with a specific irreversible inhibitor called α-difluoromethylornithine (DFMO) before exposure to MeJA vapor.

RESULTS

Mushrooms were treated with 0 or 100 µmol L^-1 MeJA or a combination of 120 µmol L^-1 DFMO and 100 µmol L^-1 MeJA, respectively, before storage at 4 °C for 21 days. Treatment with MeJA alone induced the increase in ODC activity whereas this effect was greatly suppressed by pretreatment with DFMO. α-Difluoromethylornithine strongly attenuated the effect of MeJA on decreasing cap opening, slowing the decline rate of soluble protein and total sugar, and accumulating total phenolics and flavonoids. α-Difluoromethylornithine pretreatment also counteracted the ability of MeJA to inhibit polyphenol oxidase and lipoxygenase activities, and malondialdehyde production, and to stimulate superoxide dismutase and catalase activities. It also largely downregulated MeJA-induced accumulation of free putrescine (Put).

CONCLUSION

These results reveal that ODC is involved in MeJA-regulated postharvest quality retention of button mushrooms, and this involvement is likely to be associated with Put levels. © 2018 Society of Chemical Industry.

Functional analysis of Agaricus bisporus serine proteinase 1 reveals roles in utilization of humic rich substrates and adaptation to the leaf-litter ecological niche

Agaricus bisporus is a secondary decomposer fungus and an excellent model for the adaptation, persistence and growth of fungi in humic‐rich environments such as soils of temperate woodland and pastures. The A. bisporus serine proteinase SPR1 is induced by humic acids and is highly expressed during growth on compost. Three Spr1 gene silencing cassettes were constructed around sense, antisense and non‐translatable‐stop strategies (pGRsensehph, pGRantihph and pGRstophph). Transformation of A. bisporus with these cassettes generated cultures showing a reduction in extracellular proteinase activity as demonstrated by the reduction, or abolition, of a clearing zone on plate‐based bioassays. These lines were then assessed by detailed enzyme assay, RT‐qPCR and fruiting. Serine proteinase activity in liquid cultures was reduced in 83% of transformants. RT‐qPCR showed reduced Spr1 mRNA levels in all transformants analysed, and these correlated with reduced enzyme activity. When fruiting was induced, highly‐silenced transformant AS5 failed to colonize the compost, whilst for those that did colonize the compost, 60% gave a reduction in mushroom yield. Transcriptional, biochemical and developmental observations, demonstrate that SPR1 has an important role in nutrient acquisition in compost and that SPR1 is a key enzyme in the adaptation of Agaricus to the humic‐rich ecological niche formed during biomass degradation.

Postharvest application of methyl jasmonate for improving quality retention of Agaricus bisporus fruit bodies

The influence of methyl jasmonate (MeJA) on postharvest quality and enzyme activities, gene expression level, and the functional component content linked to postharvest deterioration in Agaricus bisporus (J.E. Lange) Imbach fruit bodies was investigated. Freshly harvested fruit bodies were treated with 0 (control), 10 and 100 μM MeJA vapor at 20 °C for 12 h and then stored at 10 °C for up to 7 days. The results indicated that treatments with 100 μM MeJA vapor maintained a high level of soluble protein and total sugar, delayed browning, promoted the accumulation of phenolics and flavonoids, and inhibited the increase of respiratory rate and membrane leakage. Furthermore, 100 μM MeJA inhibited the activities of polyphenoloxidase, increased the antioxidant enzymes activities of catalase and superoxide dismutase, and lowered relative expression levels of three genes encoding polyphenol oxidase (AbPPO1, AbPPO2, and AbPPO3) throughout the storage period. Comparatively, 10 μM MeJA also had a clear beneficial effect on postharvest mushroom quality maintenance but was not as effective as 100 μM MeJA treatment. These findings suggest that application of MeJA could have potential in maintaining the quality of harvested A. bisporus fruit bodies.

A novel aspartic protease with HIV-1 reverse transcriptase inhibitory activity from fresh fruiting bodies of the wild mushroom Xylaria hypoxylon

A novel aspartic protease with HIV-1 RT inhibitory activity was isolated and characterized from fruiting bodies of the wild mushroom Xylaria hypoxylon. The purification protocol comprised distilled water homogenization and extraction step, three ion exchange chromatographic steps (on DEAE-cellulose, Q-Sepharose, and CM-cellulose in succession), and final purification was by FPLC on Superdex 75. The protease was adsorbed on all the three ion exchangers. It was a monomeric protein with a molecular mass of 43 kDa as estimated by SDS-PAGE and FPLC. Its N-terminal amino acid sequence was HYTELLSQVV, which exhibited no sequence homology to other proteases reported. The activity of the protease was adversely affected by Pepstatin A, indicating that it is an aspartic protease. The protease activity was maximal or nearly so in the pH range 6–8 and in the temperature range 35–60°C. The purified enzyme exhibited HIV-1 RT inhibitory activity with an IC₅₀ value of 8.3 μM, but was devoid of antifungal, ribonuclease, and hemagglutinating activities.

Purification and characterization of a novel serine protease from the mushroom Pholiota nameko

A novel serine protease, with a molecular mass of 19 kDa and the N-terminal sequence of ARTPEAPAEV, was isolated from dried fruiting bodies of the mushroom Pholiota nameko. The purification protocol comprised ion exchange chromatography on DEAE-cellulose, Q-Sepharose and SP-Sepharose, and gel filtration on Superdex 75. It was unadsorbed on DEAE-cellulose and Q-Sepharose but adsorbed on SP-Sepharose. It exhibited an optimum temperature at 50°C, an optimum pH at pH 8.8, a Km of 5.64 mg/mL and a Vmax of 0.98 μmol/min/mL against substrate casein. A number of metal ions inhibited the enzyme including Pb(2+), Mn(2+), Ca(2+), Hg(2+), Zn(2+), Cu(2+), Co(2+), Fe(3+) and Al(3+), with the inhibition of the last two cations being the most potent. K(+) and Mg(2+) slightly enhanced, while Li(+) moderately potentiated the activity of the protease. The protease was strongly inhibited by phenylmethylsulfonyl fluoride (PMSF), suggesting that it is a serine protease.

Recent advances in extending the shelf life of fresh Agaricus mushrooms: a review

Postharvest browning of Agaricus mushrooms is a severe problem that reduces the shelf life of harvested mushrooms because of their continued respiration and biochemical activity. There are no simple answers and no single treatment is known to limit overall quality deterioration. However, there are several strategies that are being implemented in order to reduce the rate of respiration for mushrooms. Packaging technology is the common denominator that allows us to implement these strategies and thus is key to quality preservation. In this review, first, the major factors involved in postharvest quality deterioration are discussed and then technological advances/methods used to counteract these hurdles are presented.

Trypsin-specific inhibitors from the basidiomycete Clitocybe nebularis with regulatory and defensive functions

We have isolated serine protease inhibitors from the basidiomycete Clitocybe nebularis, CnSPIs, using trypsin affinity chromatography. Full-length gene and cDNA sequences were determined for one of them, named cnispin, and the recombinant protein was expressed in Escherichia coli at high yield. The primary structure and biochemical properties of cnispin are very similar to those of the Lentinus edodes serine protease inhibitor, until now the only member of the I66 family of protease inhibitors in the MEROPS classification. Cnispin is highly specific towards trypsin, with K i in the nanomolar range. It also exhibited weaker inhibition of chymotrypsin and very weak inhibition of subtilisin and kallikrein; other proteases were not inhibited. Inhibitory activity against endogenous proteases from C. nebularis revealed a possible regulatory role for CnSPIs in the endogenous proteolytic system. Another possible biological function in defence against predatory insects was indicated by the deleterious effect of CnSPIs on the development of larvae of Drosophila melanogaster. These findings, together with the biochemical and genetic characterization of cnispin, suggest a dual physiological role for this serine protease inhibitor of the I66 MEROPS family.

Effect of different packaging films on postharvest quality and selected enzyme activities of Hypsizygus marmoreus mushrooms

Freshly harvested Hypsizygus marmoreus mushrooms were packaged using different packaging films, and physiological changes associated with postharvest deterioration, together with the activities of selected enzymes thought to play a role in senescence, were monitored during subsequent storage for 16-24 days at 4 degrees C and 65-70% relative humidity. A biaxially oriented polypropylene film (BOPP) maintained the postharvest appearance of the mushrooms most effectively by significantly reducing the incidence of unsightly aerial hyphae on the pileal surface and restricting mushroom softening. These samples also exhibited smaller initial decreases in soluble protein, smaller increases in reducing sugar content, and lower levels of malondialdehyde accumulation during early storage. Smallest increases in proteinase activity were recorded in samples wrapped with BOPP and polyoletin packaging, and superoxide dismutase and polyphenol oxidase levels were significantly higher and lower, respectively, in the former. Choice of packaging can significantly affect postharvest quality loss in H. marmoreus and improve mushroom shelf life.

Characterization of serine proteinase expression in Agaricus bisporus and Coprinopsis cinerea by using green fluorescent protein and the A. bisporus SPR1 promoter

The Agaricus bisporus serine proteinase 1 (SPR1) appears to be significant in both mycelial nutrition and senescence of the fruiting body. We report on the construction of an SPR promoter::green fluorescent protein (GFP) fusion cassette, pGreen_hph1_SPR_GFP, for the investigation of temporal and developmental expression of SPR1 in homobasidiomycetes and to determine how expression is linked to physiological and environmental stimuli. Monitoring of A. bisporus pGreen_hph1_SPR_GFP transformants on media rich in ammonia or containing different nitrogen sources demonstrated that SPR1 is produced in response to available nitrogen. In A. bisporus fruiting bodies, GFP activity was localized to the stipe of postharvest senescing sporophores. pGreen_hph1_SPR_GFP was also transformed into the model basidiomycete Coprinopsis cinerea. Endogenous C. cinerea proteinase activity was profiled during liquid culture and fruiting body development. Maximum activity was observed in the mature cap, while activity dropped during autolysis. Analysis of the C. cinerea genome revealed seven genes showing significant homology to the A. bisporus SPR1 and SPR2 genes. These genes contain the aspartic acid, histidine, and serine residues common to serine proteinases. Analysis of the promoter regions revealed at least one CreA and several AreA regulatory motifs in all sequences. Fruiting was induced in C. cinerea dikaryons, and fluorescence was determined in different developmental stages. GFP expression was observed throughout the life cycle, demonstrating that serine proteinase can be active in all stages of C. cinerea fruiting body development. Serine proteinase expression (GFP fluorescence) was most concentrated during development of young tissue, which may be indicative of high protein turnover during cell differentiation.

Hairpin-mediated down-regulation of the urea cycle enzyme argininosuccinate lyase in Agaricus bisporus

A double-stranded (ds) RNA hairpin-mediated down-regulation system was developed for the cultivated mushroom Agaricus bisporus, and the role of the urea cycle enzyme argininosuccinate lyase (asl) in mushroom post-harvest development was investigated. Hairpin expression vectors were constructed to initiate down-regulation of asl and introduced into A. bisporus by Agrobacterium tumefaciens-mediated transformation. Transcripts of asl were significantly reduced (93.1 and 99.9%) in two transformants and hairpin vector transgene sequences were maintained throughout sporophore development. Single and multiple hairpin integration events were observed in Southern analysis. Transformants with down-regulated asl exhibited reduced yield and cap expansion during post-harvest sporophore development. There were no detectable differences in urea levels between the hairpin-transformed and control strains. This is the first report of reduced gene expression resulting from the introduction of dsRNA hairpins in A. bisporus and the applications of this technology will facilitate functional studies in the mushroom.

Effect of 60Co-irradiation on postharvest quality and selected enzyme activities of Hypsizygus marmoreus fruit bodies

Hypsizygus marmoreus fruit bodies were exposed to different doses of (60)Co gamma-irradiation, stored at 4 degrees C and 65-70% relative humidity, and various physiological changes associated with postharvest deterioration, as well as the activities of selected enzymes widely considered to play a role in the process of senescence, were monitored over a subsequent storage period of 25 days. Exposure to 0.8 kGy irradiation was clearly beneficial in maintaining the postharvest appearance of the mushroom sporophores compared to non-irradiated samples and fruit bodies exposed to higher doses (1.2-2.0 kGy) of irradiation. Samples treated with 0.8 kGy also exhibited smaller initial declines in soluble protein, smaller increases in reducing sugar content, and lower levels of malondialdehyde accumulation during the early storage period. Smallest increases in proteinase activity were recorded in samples dosed with 0.8 and 2.0 kGy, and levels of superoxide dismutase were significantly higher in samples exposed to 0.8 kGy compared with non-irradiated controls. Large initial increases in catalase activity were detected in samples irradiated with 0.8, 1.2, and 1.6 kGy and, although enzyme levels gradually decreased in all samples during further storage, residual levels after 25 days were still severalfold higher in irradiated samples compared with controls. The data increase the current understanding of the effects of gamma-irradiation on the biochemical changes associated with postharvest senescence and should lead to more targeted strategies for reducing postharvest quality loss in H. marmoreus and other mushrooms.

The role of ornithine aminotransferase in fruiting body formation of the mushroom Agaricus bisporus

The complete oat gene and cDNA from the commercial mushroom, Agaricus bisporus, encoding ornithine aminotransferase (OAT) was characterized. The gene encodes a 466 amino acid protein and provides the first fully reported homobasidiomycete OAT protein sequence. The gene is interrupted by ten introns, and no mitochondrial targeting motif was present pointing to a cytoplasmic localization. The function of the gene was demonstrated by complementation of a Saccharomyces cerevisiae mutant unable to utilize ornithine as a sole source of nitrogen with an A. bisporus oat cDNA construct. Northern analysis of the oat gene together with the pruA gene (encoding Delta(1)-pyrroline-5-carboxylate dehydrogenase) showed that transcripts of both genes were lower during the first stages of fruiting body development. The higher expression of the oat gene in later stages of development, suggests the importance of ornithine metabolism for the redistribution of metabolites in the developing mushroom. Hplc analysis of all amino acids revealed that ornithine levels increased during fruiting body development whereas proline levels fell.

Argininosuccinate synthetase and argininosuccinate lyase: two ornithine cycle enzymes from Agaricus bisporus

Accumulation of high quantities of urea in fruiting bodies is a known feature of larger basidiomycetes. Argininosuccinate synthetase (ASS) and argininosuccinate lyase (ASL) are two ornithine cycle enzymes catalysing the last two steps in the arginine biosynthetic pathway. Arginine is the main precursor for urea formation. In this work the nucleotide sequences of the genes and corresponding cDNAs encoding argininosuccinate synthetase (ass) and argininosuccinate lyase (asl) from Agaricus bisporus were determined. Eight and six introns were present in the ass and asl gene, respectively. The location of four introns in the asl gene were conserved among vertebrate asl genes. Deduced amino acid sequences, representing the first homobasidiomycete ASS and ASL protein sequences, were analysed and compared with their counterparts in other organisms. The ass ORF encoded for a protein of 425 amino acids with a calculated molecular mass of 47266Da. An alignment with ASS proteins from other organisms revealed high similarity with fungal and mammalian ASS proteins, 61-63% and 51-55% identity, respectively. The asl open reading frame (ORF) encoded a protein of 464 amino acids with an calculated mass of 52337Da and similar to ASS shared the highest similarity with fungal ASL proteins, 59-60% identity. Northern analyses of ass and asl during fruiting body formation and post-harvest development revealed that expression was significantly up-regulated from developmental stage 3 on for all the tissues studied. The expression reached a maximum at the later stages of fruiting body growth, stages 6 and 7. Both ass and asl genes were up-regulated within 3h after harvest showing that the induction mechanism is very sensitive to the harvest event and emphasizes the importance of the arginine biosynthetic pathway/ornithine cycle in post-harvest physiology.

The ornithine cycle enzyme arginase from Agaricus bisporus and its role in urea accumulation in fruit bodies

An extensive survey of higher fungi revealed that members of the family Agaricaceae, including Agaricus bisporus, accumulate substantial amounts of urea in their fruit bodies. An important role of the ornithine cycle enzymes in urea accumulation has been proposed. In this work, we present the cloning and sequencing of the arginase gene and its promoter region from A. bisporus. A PCR-probe based on fungal arginase was used to identify the A. bisporus arginase gene from a cDNA library. The arginase cDNA encodes a 311-aa protein which is most likely expressed in the cytosol. Expression of the cDNA in Escherichia coli was established as a His-tagged fusion protein. The arginase gene was used as a molecular marker to study expression and regulation during sporophore formation and postharvest development. The expression of the arginase gene was significantly up-regulated from developmental stage 3 onwards for all the tissues studied. A maximum of expression was reached at stage 6 for both stipe and cap tissue. In postharvest stages 5, 6 and 7 the level of expression observed was similar to normal growth stages 5, 6 and 7. A good correlation was found between arginase expression and urea content of stipe, velum, gills, cap and peel tissue. For all tissues the urea content decreased over the first four stages of development. From stage 4 onwards urea accumulated again except for stipe tissue where no significant changes were observed. The same trend was also observed for postharvest development, but the observed increase of urea in postharvest tissues was much higher.

The cel4 gene of Agaricus bisporus encodes a beta-mannanase

Mannases have industrial uses in food and pulp industries, and their regulation may influence development of the mushrooms of commercially important basidiomycetes. We expressed an Agaricus bisporus cel4 cDNA, which encodes a mannanase, in Saccharomyces cerevisiae and Pichia pastoris. CEL4 had no detectable activity on cellulose or xylan. This gene is the first isolated from this economically important fungus to encode a mannanase. P. pastoris secreted about three times more CEL4 than S. cerevisiae. The removal of the cellulose-binding domain of CEL4 lowered the secreted specific activity by P. pastoris by approximately 97%. The genomic sequence of cel4 was isolated by screening a cosmid library of A. bisporus C54-carb8. The open reading frame was interrupted by 12 introns. The level of extracellular CEL4 increases dramatically at the postharvest stage in compost extracts of A. bisporus fruiting cultures. In laboratory liquid cultures of A. bisporus, the activity of CEL4 detected in the culture filtrate reached a maximum after 21 days. The levels of CEL4 broadly mirrored the levels of enzyme activity. In the Solka floc-bound mycelium, CEL4 protein showed a maximum after 2 to 3 weeks of culture and then declined. Changes in CEL4 activity during fruiting-body development suggest that hemicellulose utilization plays an important role in sporophore formation. The availability of the cloned gene will further studies of compost decomposition and the extracellular enzymes that fungi deploy in this process.

Cloning and postharvest expression of serine proteinase transcripts in the cultivated mushroom Agaricus bisporus

Increases in both the levels and the activity of serine proteinase have been previously described in the senescing mushroom Agaricus bisporus. cDNA encoding serine proteinase was amplified by reverse transcriptase-polymerase chain reaction using a degenerate primer based on the N-terminal sequence of a previously isolated A. bisporus serine proteinase and then cloned. The cDNA was sequenced and shown to be homologous to those of other fungal serine proteinases. Northern analysis showed that this serine proteinase gene (Spr1) was not expressed in freshly harvested sporophores but was strongly up-regulated postharvest and found almost entirely in the stipe of the sporophore (approximately 0.08% of mRNAs 2 days after harvest). Low-level expression was detectable in the flesh (pileus trama) and gill (lamellae) tissues of the cap, but none was detected in the skin (pilei pellis). In three of the cloned cDNAs, sequence analysis showed that the poly(A) tail starts at different positions. Expression of Spr1 in Escherichia coli caused restricted colony growth.

The molecular genetics of cultivated mushrooms

The types, economic significance and methods of production of the principal cultivated mushrooms are described in outline. These organisms are all less than ideal for conventional genetic analysis and breeding, so molecular methods afford a particular opportunity to advance our understanding of their biology and potentially give the prospect of improvement by gene manipulation. The sequences described are limited to those found in GenBank by August 1999. The gene sequences isolated from the white button mushroom Agaricus bisporus, the shiitake Lentinula edodes, the oyster mushrooms Pleurotus spp., the paddy straw mushroom Volvariella volvacea and the enotake Flammulina velutipes are described. The largest group are genes from A. bisporus, which includes 29 for intracellular proteins and 12 for secreted proteins. In comparison, only a total of 26 sequences can be reported for the other cultivated species. A. bisporus is also the only cultivated species for which molecular karyotyping is already supported by reliable markers for all 13 of its chromosomes.

Biochemical and physiological aspects of brown blotch disease of Agaricus bisporus

Pseudomonas tolaasii is a bacterium endemic to the compost beds where common mushroom (Agaricus bisporus) is cultivated. Under some environmental conditions still not well-determined, but influenced by temperature and relative humidity, the bacterium can become pathogenic and provoke the brown blotch disease. This review describes the interaction between P. tolaasii and A. bisporus that results in the appearance of brown spots on the mushroom caps, typical symptoms of the disease. Firstly, P. tolaasii is studied, the changes in pathogenicity are explained, the compounds that provoke the damage are enumerated as well as various experimental methods to identify the pathogenic form of the bacteria. Secondly, mechanisms involved in the formation of the brown colour on the A. bisporus caps upon infection are briefly mentioned, taking into account the enzymes that catalyse the reaction, their mechanism, substrates and reaction products. Afterwards, a detailed description of the infection process is presented step by step, starting by the chemotactical attraction, fixation, secretion of the toxins, membrane breakdown, effect of the toxin on mushroom polyphenol oxidases and on the discolouration reaction. A possible mechanism of infection is hypothesised at the molecular level. Finally, the strategies tested until now to control the disease are discussed.

Cell water balance of white button mushrooms (Agaricus bisporus) during its post-harvest lifetime studied by quantitative magnetic resonance imaging

A combination of quantitative water density and T2 MRI and changes therein observed after infiltration with 'invisible' Gd-DTPA solution was used to study cell water balances, cell water potentials and cell integrity. This method was applied to reveal the evolution and mechanism of redistribution of water in harvested mushrooms. Even when mushrooms did not lose water during the storage period, a redistribution of water was observed from stipe to cap and gills. When the storage condition resulted in a net loss of water, the stipe lost more water than the cap. The water density in the gill increased, probably due to development of spores. Deterioration effects (i.e. leakage of cells, decrease in osmotic water potential) were found in the outer stipe. They were not found in the cap, even at prolonged storage at 293 K and R.H.=70%. The changes in osmotic potential were partly accounted for by changes in the mannitol concentration. Changes in membrane permeability were also indicated. Cells in the cap had a constant low membrane (water) permeability. They developed a decreasing osmotic potential (more negative), whereas the osmotic potential in the outer stipe increased, together with the permeability of cells.

Cloning and characterization of NADP-mannitol dehydrogenase cDNA from the button mushroom, Agaricus bisporus, and its expression in response to NaCl stress

Mannitol, a six-carbon sugar alcohol, is the main storage carbon in the button mushroom, Agaricus bisporus. Given the physiological importance of mannitol metabolism in growth, fruit body development, and salt tolerance of A. bisporus, the enzyme responsible for mannitol biosynthesis, NADP-dependent mannitol dehydrogenase (MtDH) (EC 1.1.1.138), was purified to homogeneity, and MtDH cDNA was cloned, sequenced, and characterized. To our knowledge, this represents the first report on the isolation of a cDNA encoding an NADP-dependent mannitol dehydrogenase. The MtDH cDNA contains an open reading frame of 789 bp encoding a protein of approximately 28 kDa. The N-terminal and internal amino acid sequences of the deduced protein exactly matched the ones determined from the purified MtDH subunit, whereas the amino acid composition of the deduced protein was nearly identical to that of the purified MtDH. The MtDH cDNA showed high homology with a plant-induced short-chain dehydrogenase from Uromyces fabae. Phylogenetic analysis based on amino acid sequences from mannitol(-1-phosphate) dehydrogenases indicated a close relationship between the substrate specificity of the enzymes and phylogenetic differentiation. Salt-stressed fruit bodies showed an overall increase in mannitol biosynthesis, as was evident from the increase in MtDH activity, MtDH abundance, and MtDH RNA accumulation. Furthermore, the MtDH transcript level seems to be under developmental control, as MtDH RNA accumulated during maturation of the fruit body.