Pleurotus ostreatus as a model mushroom in genetics, cell biology, and material sciences

Pleurotus ostreatus, also known as the oyster mushroom, is a popular edible mushroom cultivated worldwide. This review aims to survey recent progress in the molecular genetics of this fungus and demonstrate its potential as a model mushroom for future research. The development of modern molecular genetic techniques and genome sequencing technologies has resulted in breakthroughs in mushroom science. With efficient transformation protocols and multiple selection markers, a powerful toolbox, including techniques such as gene knockout and genome editing, has been developed, and numerous new findings are accumulating in P. ostreatus. These include molecular mechanisms of wood component degradation, sexual development, protein secretion systems, and cell wall structure. Furthermore, these techniques enable the identification of new horizons in enzymology, biochemistry, cell biology, and material science through protein engineering, fluorescence microscopy, and molecular breeding. KEY POINTS: • Various genetic techniques are available in Pleurotus ostreatus. • P. ostreatus can be used as an alternative model mushroom in genetic analyses. • New frontiers in mushroom science are being developed using the fungus.

The Chromatin Modifier Protein FfJMHY Plays an Important Role in Regulating the Rate of Mycelial Growth and Stipe Elongation in Flammulina filiformis

Stipe elongation is an important process in the development of the fruiting body and is associated with the commodity quality of agaric fungi. In this study, F. filiformis was used as a model agaric fungus to reveal the function of the chromatin modifier gene containing the JmjC domain in stipe elongation. First, we identified a JmjC domain family gene (FfJmhy) with a 3684 bp length open reading frame (ORF) in F. filiformis. FfJmhy was predicted to have a histone H3K9 demethylation function, and was specifically upregulated during stipe rapid elongation. Further investigation revealed that the silencing of FfJmhy inhibited the mycelial growth, while overexpression of this gene had no effect on the mycelial growth. Comparative analysis revealed that the stipe elongation rate in FfJmhy overexpression strains was significantly increased, while it was largely reduced when FfJmhy was silenced. Taken together, these results suggest that FfJmhy positively regulates the mycelial growth and controls the elongation speed and the length of the stipe. Moreover, cell wall-related enzymes genes, including three exo-β-1,3-glucanases, one β-1,6-glucan synthase, four chitinases, and two expansin proteins, were found to be regulated by FfJmhy. Based on the putative functions of FfJmhy, we propose that this gene enhances the transcription of cell wall-related enzymes genes by demethylating histone H3K9 sites to regulate remodeling of the cell wall in rapid stipe elongation. This study provides new insight into the mechanism of rapid stipe elongation, and it is important to regulate the commodity quality of agaric fungi.

Accumulation and cross-linkage of β-1,3/1,6-glucan lead to loss of basal stipe cell wall extensibility in mushroom Coprinopsis cinerea

The mature basal stipe of mushroom Coprinopsis cinerea loses wall extensibility. We found that an endo-β-1,3-glucanase ENG from C. cinerea could restore mature basal stipe wall extensibility via pretreatment such that the ENG-pretreated basal stipe walls could be induced to extend by chitinase ChiIII. ENG pretreatment released glucose, laminaribiose, and 3-O-D-gentiobiose-D-glucose from the basal stipe walls, consistent with ENG-digested products of β-1,6-branched β-1,3-glucan. Different effects of endo-β-1,3-glucanase ENG and exo-β-1,3-glucanase EXG pretreatment on the structure, amount and ratio (β-1,3-glucoside bonds to β-1,6-glucoside bonds) of products from the basal stipe and the apical stipe cell walls, respectively, and on the cell wall extensibility and the cell wall ultra-architecture of the basal stipes were analyzed. All results demonstrate that the more accumulation and cross-linkage of β-1,6-branched β-1,3-glucan with wall maturation lead to loss of wall extensibility of the basal stipe regions compared to the apical stipe cell walls.

Glucanase-Induced Stipe Wall Extension Shows Distinct Differences from Chitinase-Induced Stipe Wall Extension of Coprinopsis cinerea

This study reports that a high concentration of the endo-β-1,3-glucanase ENG (200 μg ml^-1) induced heat-inactivated stipe wall extension of Coprinopsis cinerea, whereas a high concentration of the extracellular β-glucosidase BGL2 (1,000 μg ml^-1) did not; however, in combination, low concentrations of ENG (25 μg ml^-1) and BGL2 (260 μg ml^-1) induced heat-inactivated stipe cell wall extension. In contrast to the previously reported chitinase-reconstituted stipe wall extension, β-1,3-glucanase-reconstituted heat-inactivated stipe cell wall extension initially exhibited a fast extension rate that quickly decreased to zero after approximately 60 min; the stipe cell wall extension induced by a high concentration of β-1,3-glucanase did not result in stipe breakage during measurement, and the inner surfaces of glucanase-reconstituted extended cell walls still remained as amorphous matrices that did not appear to have been damaged. These distinctive features of the β-1,3-glucanase-reconstituted wall extension may be because chitin chains are cross-linked not only to the nonreducing termini of the side chains and the backbones of β-1,6 branched β-1,3-glucans but also to other polysaccharides. Remarkably, a low concentration of either the β-1,3-glucanase ENG or of chitinase ChiE1 did not induce heat-inactivated stipe wall extension, but a combination of these two enzymes, each at a low concentration, showed stipe cell wall extension activity that exhibited a steady and continuous wall extension profile. Therefore, we concluded that the stipe cell wall extension is the result of the synergistic actions of glucanases and chitinases.IMPORTANCE We previously reported that the chitinase could induce stipe wall extension and was involved in stipe elongation growth of the mushroom Coprinopsis cinerea In this study, we explored that β-1,3-glucanase also induced stipe cell wall extension. Interestingly, the extension profile and extended ultra-architecture of β-1,3-glucanase-reconstituted stipe wall were different from those of chitinase-reconstituted stipe wall. However, β-1,3-glucanase cooperated with chitinase to induce stipe cell wall extension. The significance of this synergy between glucanases and chitinases is that it enables a low concentration of active enzymes to induce wall extension, and the involvement of β-1,3-glucanases is necessary for the cell wall remodeling and the addition of new β-glucans during stipe elongation growth.

The Coprinopsis cinerea Tup1 homologue Cag1 is required for gill formation during fruiting body morphogenesis

The pileus (cap) of the fruiting body in homobasidiomycete fungi bears the hymenium, a layer of cells that includes the basidia where nuclear fusion, meiosis and sporulation occur. Coprinopsis cinerea is a model system for studying fruiting body development. The hymenium of C. cinerea forms at the surface of the gills in the pileus. In a previous study, we identified a mutation called cap-growthless1-1 (cag1-1) that blocks gill formation, which yields primordia that never mature. In this study, we found that the cag1 gene encodes a homologue of Saccharomyces cerevisiae Tup1. The C. cinerea genome contains another Tup1 homologue gene called Cc.tupA. Reciprocal tagging of Cag1 and Cc.TupA with green and red fluorescent proteins revealed that the relative ratios of the amounts of the two Tup1 paralogues varied among tissues. Compared with Cc.TupA, Cag1 was preferentially expressed in the gill trama tissue cells, suggesting that the function of Cag1 is required for gill trama tissue differentiation and maintenance. Yeast two-hybrid analysis and co-localisation of Cag1 and Cc.TupA suggested that Cag1 interacts with Cc.TupA in the nuclei of certain cells.

Summary: Cag1, a Tup1 homologue in Coprinopsis cinerea, is required for gill formation in fruiting body development and is highly expressed in the central region of gills.

Characterization of stipe elongation of the mushroom Coprinopsis cinerea

Previously, we observed an acid-induced short-term wall extension in Flammulina velutipes apical stipes during a 15 min period after a change from a neutral to an acidic pH. This acid-induced stipe wall extension was eliminated by heating and reconstituted by a snail expansin-like protein, although we failed to isolate any endogenous expansin-like protein from F. velutipes because of its limited 1 mm fast elongation region. In this study, we report that Coprinopsis cinerea stipes possess a 9 mm fast elongation apical region, which is suitable as a model material for wall extension studies. The elongating apical stipe showed two phases of acid-induced wall extension, an initial quick short-term wall extension during the first 15 min and a slower, gradually decaying long-term wall extension over the subsequent 2 h. After heating or protein inactivation pretreatment, apical stipes lost the long-term wall extension, retaining a slower short-term wall extension, which was reconstituted by an expansin-like snail protein. In contrast, the non-elongating basal stipes showed only a weaker short-term wall extension. We propose that the long-term wall extension is a protein-mediated process involved in stipe elongation, whereas the short-term wall extension is a non-protein mediated process not involved in stipe elongation.

Gene expression profiling reveals large regulatory switches between succeeding stipe stages in Volvariella volvacea

The edible mushroom Volvariella volvacea is an important crop in Southeast Asia and is predominantly harvested in the egg stage. One of the main factors that negatively affect its yield and value is the rapid transition from the egg to the elongation stage, which has a decreased commodity value and shelf life. To improve our understanding of the changes during stipe development and the transition from egg to elongation stage in particular, we analyzed gene transcription in stipe tissue of V. volvacea using 3′-tag based digital expression profiling. Stipe development turned out to be fairly complex with high numbers of expressed genes, and regulation of stage differences is mediated mainly by changes in expression levels of genes, rather than on/off modulation. Most explicit is the strong up-regulation of cell division from button to egg, and the very strong down-regulation hereof from egg to elongation, that continues in the maturation stage. Button and egg share cell division as means of growth, followed by a major developmental shift towards rapid stipe elongation based on cell extension as demonstrated by inactivation of cell division throughout elongation and maturation. Examination of regulatory genes up-regulated from egg to elongation identified three potential high upstream regulators for this switch. The new insights in stipe dynamics, together with a series of new target genes, will provide a sound base for further studies on the developmental mechanisms of mushroom stipes and the switch from egg to elongation in V. volvacea in particular.

Stipe wall extension of Flammulina velutipes could be induced by an expansin-like protein from Helix aspersa

Expansin proteins extend plant cell walls by a hydrolysis-free process that disrupts hydrogen bonding between cell wall polysaccharides. However, it is unknown if this mechanism is operative in mushrooms. Herein we report that the native wall extension activity was located exclusively in the 10 mm apical region of 30 mm Flammulina velutipes stipes. The elongation growth was restricted also to the 9 mm apical region of the stipes where the elongation growth of the 1st millimetre was 40-fold greater than that of the 5th millimetre. Therefore, the wall extension activity represents elongation growth of the stipe. The low concentration of expansin-like protein in F. velutipes stipes prevented its isolation. However, we purified an expansin-like protein from snail stomach juice which reconstituted heat-inactivated stipe wall extension without hydrolytic activity. So the previous hypotheses that stipe wall extension was resulted from hydrolysis of wall polymers by enzymes or disruption of hydrogen bonding of wall polymers exclusively by turgor pressure are challenged. We suggest that stipe wall extension may be mediated by endogenous expansin-like proteins that facilitate cell wall polymer slippage by disrupting noncovalent bonding between glucan chains or chitin chains.

The Coprinopsis cinerea septin Cc.Cdc3 is involved in stipe cell elongation

We have identified and characterized a Coprinopsis cinerea mutant defective in stipe elongation during fruiting body development. In the wild-type, stipe cells elongate at the maturation stage of fruiting, resulting in very slender cells. In the mutant, the stipe cells fail to elongate, but become rather globular at the maturation stage. We found that the mutant phenotype is rescued by a gene encoding a homolog of Saccharomyces cerevisiae CDC3 septin, Cc.Cdc3. The C. cinerea genome includes 6 septin genes, 5 of which, including Cc.cdc3, are highly transcribed during stipe elongation in the wild type. In the mutant, the level of Cc.cdc3 transcription in the stipe cells remains the same as that in the mycelium, and the level of Cc.cdc10 transcription is approximately 100 times lower than that in the wild-type stipe cells. No increase in transcription of Cc.cdc3 in the mutant may be due to the fact that the Cc.cdc3 gene has a 4-base pair insertion in its promoter and/or that the promoter region is methylated in the mutant. Overexpressed EGFP-Cc.Cdc3 fusion protein rescues the stipe elongation in the transformants, localizes to the cell cortex and assembles into abundant thin filaments in the elongating stipe cells. In contrast, in vegetative hyphae, EGFP-Cc.Cdc3 is localized to the hyphal tips of the apical cells of hyphae. Cellular defects in the mutant, combined with the localization of EGFP-Cc.Cdc3, suggest that septin filaments in the cell cortex provide the localized rigidity to the plasma membrane and allow cells to elongate cylindrically.

Endo-β-1,3-glucanase GLU1, from the fruiting body of Lentinula edodes, belongs to a new glycoside hydrolase family

The cell wall of the fruiting body of the mushroom Lentinula edodes is degraded after harvesting by enzymes such as β-1,3-glucanase. In this study, a novel endo-type β-1,3-glucanase, GLU1, was purified from L. edodes fruiting bodies after harvesting. The gene encoding it, glu1, was isolated by rapid amplification of cDNA ends (RACE)-PCR using primers designed from the N-terminal amino acid sequence of GLU1. The putative amino acid sequence of the mature protein contained 247 amino acid residues with a molecular mass of 26 kDa and a pI of 3.87, and recombinant GLU1 expressed in Pichia pastoris exhibited β-1,3-glucanase activity. GLU1 catalyzed depolymerization of glucans composed of β-1,3-linked main chains, and reaction product analysis by thin-layer chromatography (TLC) clearly indicated that the enzyme had an endolytic mode. However, the amino acid sequence of GLU1 showed no significant similarity to known glycoside hydrolases. GLU1 has similarity to several hypothetical proteins in fungi, and GLU1 and highly similar proteins should be classified as a novel glycoside hydrolase family (GH128).

Characterization of the post-harvest changes in gene transcription in the gill of the Lentinula edodes fruiting body

We compared the gene expression patterns of Lentinula edodes fresh fruiting bodies and fruiting bodies 3 days after harvest, by suppression subtractive hybridization, to characterize the physiologic changes that occur after harvest, such as gill browning and cell wall lysis of the fruiting body, which are responsible for the loss of food quality and value. We found increase of transcription levels of several enzyme encoding genes, such as, two phenol oxidases encoding genes (tyr tyrosinase, lcc4 laccase), and several cell wall degradation-related enzyme-encoding genes, such as mixed-linked glucanase (mlg1), chitinases (chi1, chi2), chitin deacetylase (chd1), and chitosanase (cho1), after harvesting. We isolated a putative transcription factor-encoding gene (L. edodes exp1) with high similarity to exp1 from Coprinopsis cinerea, which is involved in autolysis of the cap during spore diffusion. Transcription of L. edodes exp1 increased post-harvest, which suggests that its target genes are up-regulated after harvesting. These enzymes and the transcription factor may be involved in L. edodes fruiting body senescence.

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.

Lentinula edodes tlg1 encodes a thaumatin-like protein that is involved in lentinan degradation and fruiting body senescence

Lentinan is an antitumor product that is purified from fresh Lentinula edodes fruiting bodies. It is a cell wall component, comprising beta-1,3-glucan with beta-1,6-linked branches, which becomes degraded during postharvest preservation as a result of increased glucanase activity. In this study, we used N-terminal amino acid sequence to isolate tlg1, a gene encoding a thaumatin-like (TL) protein in L. edodes. The cDNA clone was approximately 1.0 kb whereas the genomic sequence was 2.1 kb, and comparison of the two indicated that tlg1 contains 12 introns. The tlg1 gene product (TLG1) was predicted to comprise 240 amino acids, with a molecular mass of 25 kD and isoelectric point value of 3.5. The putative amino acid sequence exhibits approximately 40% identity with plant TL proteins, and a fungal genome database search revealed that these TL proteins are conserved in many fungi including the basidiomycota and ascomycota. Transcription of tlg1 was not detected in vegetative mycelium or young and fresh mushrooms. However, transcription increased following harvest. Western-blot analysis demonstrated a rise in TLG1 levels following harvest and spore diffusion. TLG1 expressed in Escherichia coli and Aspergillus oryzae exhibited beta-1,3-glucanase activity and, when purified from the L. edodes fruiting body, demonstrated lentinan degrading activity. Thus, we suggest that TLG1 is involved in lentinan and cell wall degradation during senescence following harvest and spore diffusion.

Biomechanics of stipe elongation in the basidiomycete Coprinopsis cinerea

Stipe elongation in fruit bodies of Coprinopsis cinerea (syn. Coprinus cinereus) was examined from a biomechanical perspective. Two strains were studied: the self-compatible Amut Bmut homokaryon that produces normal fruit bodies with relatively short stipes, and mutant B1918 that produces abnormally elongated stipes. Measurements of the pressure exerted by developing mushrooms were made using strain gauges, and these data were compared with measurements of the pressures exerted by vegetative hyphae of the same strains. The experiments demonstrate that AmutBmut hyphae elongating within stipe tissue push with the same pressure (approx. 0.5 atmosphere) as vegetative hyphae growing through their food sources. In purely biomechanical terms, the fruit body may therefore be viewed as a relatively uncomplicated sum of its parts. Analysis of the mutant strain B1918 demonstrated that hyperelongation of the stipe is not associated with any difference in the pressure exerted by the fruit body. The fault in the mechanism of stipe extension in B1918 may be reflected in the increased fluidity of the cell wall of vegetative hyphae of this strain, but further work is necessary to resolve this.

Ligand interactions of the Coprinopsis cinerea galectins

The basidiomycete Coprinopsis cinerea (Coprinus cinereus) expresses two fruiting body-specific isolectins (CGL1 and CGL2) that belong to the family of galectins. Understanding the role of these beta-galactoside binding lectins is still in the beginning. Even though the prerequisites for substrate binding are well understood, it is not known how discrimination between potential substrates is achieved and what kind of influence this has on the function in a distinct cellular context. Precise knowledge of the expression of galectins and their ligands will aid in elucidating their function. In Coprinopsis, the developmentally regulated ligands for galectins co-localise with galectin expression in the veil surrounding the developing primordium and the outer cells of the young stipe. In addition, galectin ligands are observed in the hymenium. The subcellular localisation of the galectin ligands suggests these to be present in cellular compartments distinct from galectin transport. The sensitivity of the in situ interactions with exogenous galectin towards detergents and organic solvents infers that these ligands are lipid-borne. Accordingly, lipid fractions from primordia are shown to contain galectin-binding compounds. Based on these results and the determined binding specificity towards substituted beta-galactosides we hypothesise that beta-galactoside-containing lipids (basidiolipids) found in mushrooms are physiological ligands for the galectins in C. cinerea.

Isolation and characterization of a fruiting body-specific exo-beta-1,3-glucanase-encoding gene, exg1, from Lentinula edodes

An exo-beta-1,3-glucanase-encoding gene was isolated from Lentinula edodes to investigate the relationship between the cell wall lytic enzyme and mushroom morphogenesis. The deduced amino acid sequence of the protein corresponding to the exg1 gene displayed 67% identity to AbEXG1 of Agaricus bisporus and approximately 40% identity to yeast exo-beta-1,3-glucanases. Two conserved glutamic acids within the catalytic active site in yeast exo-beta-1,3-glucanases were conserved in exg1 of L. edodes. The exg1 gene was expressed in fruiting bodies, but not in vegetative mycelia. Expression was higher in the stipe than in the pileus of young fruiting bodies. The gene was additionally expressed in the gills of mature fruiting bodies. We purified a glucanase from the stipes of young fruiting bodies that had an N-terminus identical to that of the putative exg1 product. These results collectively indicate that exg1 is involved in L. edodes fruiting body development, including stipe elongation.

The eln3 gene involved in fruiting body morphogenesis of Coprinus cinereus encodes a putative membrane protein with a general glycosyltransferase domain

We identified and characterized elongationless3 (eln3-1), a restriction enzyme-mediated integration (REMI) mutation affecting fruiting body morphogenesis in Coprinus cinereus. The mutant produces an aberrant fruiting body in which the stipe hardly elongates during fruiting body maturation. In the wild type, cylindrical stipe cells, elongation growth of which is responsible for stipe elongation, make side-by-side contact with one another and run parallel to the stipe axis, whereas in the mutant, the organization of the stipe tissue is disturbed and much space is produced between stipe cells. This disorganization of the stipe tissue, together with reduced elongation of the stipe cells, causes the mutant stipe short and bulgy. After a plasmid rescue, the eln3 gene was identified as a DNA fragment that complements the eln3-1 mutation. The eln3 ORF is predicted to encode a protein of 927 amino acids with a general glycosyltransferase domain and to be located in the plasma membrane. Transcription of the eln3 gene is specifically activated in rapidly elongating stipes. Possible involvement of the putative Eln3 enzyme in cell-to-cell connection is discussed.

Life history and developmental processes in the basidiomycete Coprinus cinereus

Coprinus cinereus has two main types of mycelia, the asexual monokaryon and the sexual dikaryon, formed by fusion of compatible monokaryons. Syngamy (plasmogamy) and karyogamy are spatially and temporally separated, which is typical for basidiomycetous fungi. This property of the dikaryon enables an easy exchange of nuclear partners in further dikaryotic-monokaryotic and dikaryotic-dikaryotic mycelial fusions. Fruiting bodies normally develop on the dikaryon, and the cytological process of fruiting-body development has been described in its principles. Within the specialized basidia, present within the gills of the fruiting bodies, karyogamy occurs in a synchronized manner. It is directly followed by meiosis and by the production of the meiotic basidiospores. The synchrony of karyogamy and meiosis has made the fungus a classical object to study meiotic cytology and recombination. Several genes involved in these processes have been identified. Both monokaryons and dikaryons can form multicellular resting bodies (sclerotia) and different types of mitotic spores, the small uninucleate aerial oidia, and, within submerged mycelium, the large thick-walled chlamydospores. The decision about whether a structure will be formed is made on the basis of environmental signals (light, temperature, humidity, and nutrients). Of the intrinsic factors that control development, the products of the two mating type loci are most important. Mutant complementation and PCR approaches identified further genes which possibly link the two mating-type pathways with each other and with nutritional regulation, for example with the cAMP signaling pathway. Among genes specifically expressed within the fruiting body are those for two galectins, beta-galactoside binding lectins that probably act in hyphal aggregation. These genes serve as molecular markers to study development in wild-type and mutant strains. The isolation of genes for potential non-DNA methyltransferases, needed for tissue formation within the fruiting body, promises the discovery of new signaling pathways, possibly involving secondary fungal metabolites.

A mutation in the eln2 gene encoding a cytochrome P450 of Coprinus cinereus affects mushroom morphogenesis

A dominant mutation of the elongationless2 (eln2) gene of the mushroom Coprinus cinereus (eln2-1) affects pattern formation in the development of fruit body primordia, causing dumpy primordia which culminate in mature fruit bodies with short stipes. Phenotypic analyses revealed disturbance of tissue organization and cell morphogenesis in the primordial shaft and suggested that the defects in the primordial shaft interfere with differentiation of the stipe tissue in the mutant primordia. The eln2 locus was assigned to chromosome XII and the eln2-1 mutant gene was cloned from a chromosome XII-specific cosmid library as a genomic fragment that brings about the dominant mutant phenotype. The eln2 gene encodes a novel type of microsomal cytochrome P450 enzyme (CYP502) and is constitutively expressed. The eln2-1 mutation is a 4-bp deletion in the 3'-terminal region of the gene, leading to truncation of C-terminal 18 amino acids. We suggest that the truncation affects the activity of the CYP502 enzyme.