Novel chitosanase from Streptomyces griseus HUT 6037 with transglycosylation activity

Streptomyces griseus HUT 6037 inducibly produced two chitosanases when grown on chitosan. To elucidate the mechanism of degradation of chitinous compound by this strain, chitosanases I and II of S. griseus HUT 6037 were purified and characterized. The purified enzymes had a molecular mass of 34 kDa. Their optimum pH was 5.7, and their optimum temperature was 60 degrees C. They hydrolyzed not only partially deacetylated chitosan, but also carboxymethylcellulose. Time-dependent 1H-NMR spectra showing hydrolysis of (GlcN)6 by the chitosanases were obtained for identification of the anomeric form of the reaction products. Both chitosanases produced the beta-form specifically, indicating that they were retaining enzymes. These enzymes catalyzed a glycosyltransfer reaction in the hydrolysis of chitooligosaccharides. The N-terminal and internal amino acid sequences of chitosanase II were identified. A PCR fragment corresponding to these amino acid sequences was used to screen a genomic library for the entire gene encoding chitosanase II. Sequencing of the choII gene showed an open reading frame encoding a protein with 359 amino acid residues. The deduced primary structure was similar to endoglucanase E-5 of Thermomonospora fusca, which enzyme belongs to family 5 of the glycosyl hydrolases. This is the first report of a family 5 chitosanase with transglycosylation activity.

Abnormal 'wrinkled' cell walls and retarded development of transgenic Arabidopsis thaliana plants expressing endo-1,4-beta-glucanase (cell) antisense

Transgenic Arabidopsis thaliana plants expressing cel1 antisense exhibit reduced levels of cel1 mRNA and protein compared with wild-type plants. The former display significant alterations in their phenotype. cel1 antisense plants have shorter stems and roots and are mechanically weaker than their wild-type counterparts. In cel1 antisense plants, the cell wall structure is markedly disrupted: both fluorescent confocal microscopy and scanning electron microscopy revealed 'wrinkled' cell walls, thus indicating that CEL1 plays an important role in cell wall relaxation during cell growth and expansion. In cel1 antisense plants, the number of xylem elements per bundle is smaller than in the wild-type. In addition, both xylem elements and interfascicular fibers are significantly less lignified in the former. It is suggested that in A. thaliana, abnormal cell wall deposition affected by CEL1 depletion is associated not only with cell growth, but also with the differentiation process in the vascular and supporting tissues.

CelI, a noncellulosomal family 9 enzyme from Clostridium thermocellum, is a processive endoglucanase that degrades crystalline cellulose

The family 9 cellulase gene celI of Clostridium thermocellum, was previously cloned, expressed, and characterized (G. P. Hazlewood, K. Davidson, J. I. Laurie, N. S. Huskisson, and H. J. Gilbert, J. Gen. Microbiol. 139:307-316, 1993). We have recloned and sequenced the entire celI gene and found that the published sequence contained a 53-bp deletion that generated a frameshift mutation, resulting in a truncated and modified C-terminal segment of the protein. The enzymatic properties of the wild-type protein were characterized and found to conform to those of other family 9 glycoside hydrolases with a so-called theme B architecture, where the catalytic module is fused to a family 3c carbohydrate-binding module (CBM3c); CelI also contains a C-terminal CBM3b. The intact recombinant CelI exhibited high levels of activity on all cellulosic substrates tested, with pH and temperature optima of 5.5 and 70 degrees C, respectively, using carboxymethylcellulose as a substrate. Native CelI was capable of solubilizing filter paper, and the distribution of reducing sugar between the soluble and insoluble fractions suggests that the enzyme acts as a processive cellulase. A truncated form of the enzyme, lacking the C terminal CBM3b, failed to bind to crystalline cellulose and displayed reduced activity toward insoluble substrates. A truncated form of the enzyme, in which both the cellulose-binding CBM3b and the fused CBM3c were removed, failed to exhibit significant levels of activity on any of the substrates examined. This study underscores the general nature of this type of enzymatic theme, whereby the fused CBM3c plays a critical accessory role for the family 9 catalytic domain and changes its character to facilitate processive cleavage of recalcitrant cellulose substrates.

Isolation and promoter analysis of two genes encoding different endo-beta-1,4-glucanases in the non-climacteric strawberry

Two endo-beta-1,4-glucanase (EGase; EC 3.2.1.4.) genes, highly expressed during ripening of the non-climacteric strawberries (Fragariaxananassa Duch. cv. Chandler), were isolated. Serial promoter deletions of both genes (i.e. FaEG1 and FaEG3) fused to GUS were transiently assayed in strawberry fruits by using a technique recently developed in this laboratory. Although differences were observed with the short fragments, GUS activity became comparable with the largest fragments of both promoters. The apparently similar strength of the two largest promoter fragments was in contrast with previous results of Northern analyses which demonstrated different transcripts amounts for the two genes. The inclusion of the 3' flanking region of both genes in the transient assays showed that, in the case of FaEG3, the 3' region had a down-regulating effect on the expression of GUS, and this might account for the lower amount of FaEG3 mRNA usually observed in ripe fruits compared to that of FaEG1. Downstream instability elements might be involved in such down-regulation.

Characterization of a cellulase containing a family 30 carbohydrate-binding module (CBM) derived from Clostridium thermocellum CelJ: importance of the CBM to cellulose hydrolysis

Clostridium thermocellum CelJ is a modular enzyme containing a family 30 carbohydrate-binding module (CBM) and a family 9 catalytic module at its N-terminal moiety. To investigate the functions of the CBM and the catalytic module, truncated derivatives of CelJ were constructed and characterized. Isothermal titration calorimetric studies showed that the association constants (K(a)) of the CBM polypeptide (CBM30) for the binding of cellopentaose and cellohexaose were 1.2 x 10(4) and 6.4 x 10(4) M(-1), respectively, and that the binding of CBM30 to these ligands is enthalpically driven. Qualitative analyses showed that CBM30 had strong affinity for cellulose and beta-1,3-1,4-mixed glucan such as barley beta-glucan and lichenan. Analyses of the hydrolytic action of the enzyme comprising the CBM and the catalytic module showed that the enzyme is a processive endoglucanse with strong activity towards carboxymethylcellulose, barley beta-glucan and lichenan. By contrast, the catalytic module polypeptide devoid of the CBM showed negligible activity toward these substrates. These observations suggest that the CBM is extremely important not only because it mediates the binding of the enzyme to the substrates but also because it participates in the catalytic function of the enzyme or contributes to maintaining the correct tertiary structure of the family 9 catalytic module for expressing enzyme activity.

ACEI of Trichoderma reesei is a repressor of cellulase and xylanase expression

We characterized the effect of deletion of the Trichoderma reesei (Hypocrea jecorina) ace1 gene encoding the novel cellulase regulator ACEI that was isolated based on its ability to bind to and activate in vivo in Saccharomyces cerevisiae the promoter of the main cellulase gene, cbh1. Deletion of ace1 resulted in an increase in the expression of all the main cellulase genes and two xylanase genes in sophorose- and cellulose-induced cultures, indicating that ACEI acts as a repressor of cellulase and xylanase expression. Growth of the strain with a deletion of the ace1 gene on different carbon sources was analyzed. On cellulose-based medium, on which cellulases are needed for growth, the Deltaace1 strain grew better than the host strain due to the increased cellulase production. On culture media containing sorbitol as the sole carbon source, the growth of the strain with a deletion of the ace1 gene was severely impaired, suggesting that ACEI regulates expression of other genes in addition to cellulase and xylanase genes. A strain with a deletion of the ace1 gene and with a deletion of the ace2 gene coding for the cellulase and xylanase activator ACEII expressed cellulases and xylanases similar to the Deltaace1 strain, indicating that yet another activator regulating cellulase and xylanase promoters was present.

Purification, characterization, cloning, and expression of a novel xyloglucan-specific glycosidase, oligoxyloglucan reducing end-specific cellobiohydrolase

A novel oligoxyloglucan-specific glycosidase, oligoxyloglucan reducing end-specific cellobiohydrolase (OXG-RCBH), with a molecular mass of 97 kDa and a pI of 6.1, was isolated from the fungus Geotrichum sp. M128. Analysis of substrate specificity using various xyloglucan oligosaccharide structures revealed that OXG-RCBH had exoglucanase activity. It recognized the reducing end of oligoxyloglucan and released two glucosyl residue segments from the main chain. The full-length cDNA encoding OXG-RCBH was cloned and sequenced, and it had a 2436-bp open reading frame encoding an 812amino acid protein. The deduced protein showed approximately 35% identity to members of glycoside hydrolase family 74. The cDNA encoding OXG-RCBH was then expressed in Escherichia coli. Although the recombinant protein was expressed as an inclusion body, renaturation was successful, and enzymatically active recombinant OXG-RCBH was obtained.

Gene cloning, sequencing, and characterization of a family 9 endoglucanase (CelA) with an unusual pattern of activity from the thermoacidophile Alicyclobacillus acidocaldarius ATCC27009

A gene encoding a beta-1,4-glucanase (CelA) belonging to subfamily E1 of family 9 of glycoside hydrolases was cloned and sequenced from the gram-positive thermoacidophile Alicyclobacillus acidocaldarius strain ATCC27009. The translated protein contains an immunoglobulin-like domain but lacks a cellulose-binding domain. The enzyme, when overproduced in Escherichia coli and purified, displayed a temperature optimum of 70 degrees C and a pH optimum of 5.5. CelA contained one zinc and two calcium atoms. Calcium and zinc are likely to be important for temperature stability. The enzyme was most active against substrates containing beta-1,4-linked glucans (lichenan and carboxy methyl cellulose), but also exhibited activity against oat spelt xylan. A striking pattern of hydrolysis on p-nitrophenyl-glycosides was observed, with highest activity on the cellobioside derivative, some on the cellotetraoside derivative, and none on the glucoside and cellotrioside derivatives. Unmodified cellooligosaccharides were also hydrolyzed by CelA. No signal peptide for transport across the cytoplasmic membrane was detected. This, together with the substrate specificity displayed, near neutral pH optimum and irreversible inactivation at low pH, suggests a role for CelA as a cytoplasmic enzyme for the degradation of imported oligosaccharides.

Structure of the Humicola insolens cellobiohydrolase Cel6A D416A mutant in complex with a non-hydrolysable substrate analogue, methyl cellobiosyl-4-thio-beta-cellobioside, at 1.9 A

The enzymatic degradation of cellulose continues to be one of the most important enzyme-catalysed reactions. Glycoside hydrolases from family GH-6 hydrolyse cellulose with inversion of the configuration of the anomeric carbon. Whilst the catalytic proton donor has been clearly identified (Asp226 in Humicola insolens Cel6A), the identification and even the existence of a potential Brønsted base remains unclear. Equally controversial is the role of surface-loop flexibility. Here, the structure of the D416A mutant of the H. insolens cellobiohydrolase Cel6A in complex with a non-hydrolysable thiooligosaccharide methyl cellobiosyl-4-thio-beta-cellobioside at 1.9 A resolution is presented. Substrate distortion in the -1 subsite, to a (2)S(0) skew-boat conformation, is observed, similar to that seen in the analogous Trichoderma reesei Cel6A structure [Zou et al. (1999), Structure, 7, 1035-1045], but the active-centre N-terminal loop of the H. insolens enzyme is found in a more open conformation than described for previous structures.

Towards understanding the role of membrane-bound endo-beta-1,4-glucanases in cellulose biosynthesis

Recent studies have highlighted the involvement of membrane-anchored endo-beta-1,4-glucanases in cellulose biosynthesis in plants, suggesting that there are parallels with Agrobacterium tumefaciens and other bacteria which also require endo-beta-1,4-glucanases for cellulose synthesis. This review summarises recent literature on endo-beta-1,4-glucanases and their role in plant development and addresses the possible functions of membrane-anchored isoforms in the synthesis of cellulose.

Effect of single active-site cleft mutation on product specificity in a thermostable bacterial cellulase

Mutation of a single active-site cleft tyrosyl residue to a glycyl residue significantly changes the mixture of products released from phosphoric acid-swollen cellulose (PSC) by EIcd, the catalytic domain of the endoglucanase-I from Acidothermus cellulolyticus. The percentage of glucose in the product stream is almost 40% greater for the Y245G mutant (and for an additional double mutant, Y245G/Q204A) than for the wild type enzyme. Comparisons of results for digestion PSC and of pretreated yellow poplar suggest that the observed shifts in product specificity are connected to the hydrolysis of a more easily digestible fraction of both substrates. A model is presented that relates the changes in product specificity to a mutation-driven shift in indexing of the polymeric substrate along the extended binding-site cleft.

Characterization of the cellulolytic complex (cellulosome) of Clostridium acetobutylicum

A large cellulosomal gene cluster was identified in the recently sequenced genome of Clostridium acetobutylicum ATCC 824. Sequence analysis revealed that this cluster contains the genes for the scaffolding protein CipA, the processive endocellulase Cel48A, several endoglucanases of families 5 and 9, the mannanase Man5G, and a hydrophobic protein, OrfXp. Surprisingly, genetic organization of this large cluster is very similar to that of Clostridium cellulolyticum, the model of mesophilic clostridial cellulosomes. As C. acetobutylicum is unable to grow on cellulosic substrates, the existence of a cellulosomal gene cluster in the genome raises questions about its expression, function and evolution. Biochemical evidence for the expression of a cellulosomal protein complex was investigated. The results of sodium dodecyl sulfate-polyacrylamide gel electrophoresis, N-terminal sequencing and Western blotting with antibodies against specific components of the C. cellulolyticum cellulosome suggest that at least four major cellulosomal proteins are present. In addition, despite the fact that no cellulolytic activities were detected, we report here the evidence for the production of a high molecular mass cellulosomal complex in C. acetobutylicum.

Biochemical characterization of Thermotoga maritima endoglucanase Cel74 with and without a carbohydrate binding module (CBM)

The genome of the hyperthermophilic bacterium Thermotoga maritima (Tm) encodes at least eight glycoside hydrolases with putative signal peptides; the biochemical characteristics of seven of these have been reported previously. The eighth, Tm Cel74, is encoded by an open reading frame of 2124 bp corresponding to a polypeptide of 79 kDa with a signal peptide at the amino-terminus. The gene (lacking the signal peptide) encoding Tm Cel74 was expressed as a 77 kDa monomeric polypeptide in Escherichia coli and found to be optimally active at pH 6, 90 degrees C, with a melting temperature of approximately 105 degrees C. The cel74 gene was previously found to be induced during T. maritima growth on a variety of polysaccharides, including barley glucan, carboxymethyl cellulose (CMC), glucomannan, galactomannan and starch. However, while Tm Cel74 was most active towards barley glucan and to a lesser extent CMC, glucomannan and tamarind (xyloglucan), no activity was detected on other glycans, including galactomannan, laminarin and starch. Also, Tm Cel74 did not contain a carbohydrate binding module (CBM), versions of which have been identified in the amino acid sequences of other family 74 enzymes. As such, a CBM associated with a chitinase in another hyperthermophile, Pyrococcus furiosus, was used to create a fusion protein that was active on crystalline cellulose; Tm Cel74 lacked activity on this substrate. Based on the cleavage pattern determined for Tm Cel74 on glucan-based substrates, this enzyme likely initiates recruitment of carbohydrate carbon and energy sources by creating oligosaccharides that are transported into the cell for further processing.

Transcript analysis of genes encoding a family 61 endoglucanase and a putative membrane-anchored family 9 glycosyl hydrolase from Phanerochaete chrysosporium

Phanerochaete chrysosporium cellulase genes were cloned and characterized. The cel61A product was structurally similar to fungal endoglucanases of glycoside hydrolase family 61, whereas the cel9A product revealed similarities to Thermobifida fusca Cel9A (E4), an enzyme with both endo- and exocellulase characteristics. The fungal Cel9A is apparently a membrane-bound protein, which is very unusual for microbial cellulases. Transcript levels of both genes were substantially higher in cellulose-grown cultures than in glucose-grown cultures. These results show that P. chrysosporium possesses a wide array of conventional and unconventional cellulase genes.

New endo-beta-1,4-glucanases from the parabasalian symbionts, Pseudotrichonympha grassii and Holomastigotoides mirabile of Coptotermes termites

Abstract. An endo-beta-1,4-glucanase (EG) was purified from the hindgut of an Australian mound-building termite, Coptotermes lacteus. The hindgut extract had a peak separate from those for extracts obtained from the salivary glands and the midgut based on sephacryl S-200 gel chromatography, and also demonstrated an origin different from the endogenous EGs of the termite itself. The recovery was further purified by SDS-PAGE, and its N-terminal amino acid sequence analyzed. This showed high homology to EGs from glycoside hydrolase family (GHF) 7. PCR-based cloning methods were applied to the hindgut contents of C. lacteus and individual protozoan symbionts from C formosanus. cDNAs encoding putative EGs homologous to GHF7 members were then identified. The functionality of one of the putative proteins was confirmed by its expression in Escherichia coli.

Regulation by carbon and nitrogen sources of a family of cellulases in Aspergillus nidulans

The total amount of Aspergillus nidulans secreted cellulases is affected by both the carbon and nitrogen source present in the medium, and is regulated directly and/or indirectly by the carbon metabolism regulators, CreA, CreB, and CreC, and the global nitrogen metabolism regulator, AreA. We have characterized two A. nidulans genes that encode exo-cellulases, and one gene that encodes an endo-cellulase which is additional to the previously described endo-cellulase encoding gene, eglA. The putative regulatory regions 5(') of all the genes contain potential binding sites for the global carbon and nitrogen regulatory proteins, CreA and AreA. The sequences 5(') of eglA and eglB also contain potential consensus binding sites for XlnR which is involved in induction in Aspergillus niger, but none of the 5(') sequences contains an exact copy of the AceII DNA binding consensus sequence involved in induction in Trichoderma reesei, and thus it is likely that they may be induced by different pathway specific regulatory proteins.

Biolistic transformation of Trichoderma reesei using the Bio-Rad seven barrels Hepta Adaptor system

Effective biolistic transformation of intact conidia from the filamentous fungus Trichoderma reesei was achieved using the Bio-Rad Hepta Adaptor system with seven barrels for particle launch. Transformation frequencies of up to 39 colonies per microg of circular DNA and 37 colonies per microg of linear DNA were obtained at an optimal target distance of 3 cm and a helium pressure of 1350 psi. These values are about 3.5- to 6-fold higher than transformant yields reported earlier for T. reesei using the hygromycin phosphotransferase (hph) gene conferring resistance to the antibiotic hygromycin B as a selectable marker in combination with the PDS-1000/He single barrel system. High mitotic stability of the transformants (98-100%) was demonstrated. The Hepta Adaptor device allowing bombardment of seven lots of conidia in a single plate offers clear advantage in terms of transformant numbers over the single barrel system where target cells are restricted to the center of the plate.

Functional analysis of regulatory elements in the gene promoter for an abscission-specific cellulase from bean and isolation, expression, and binding affinity of three TGA-type basic leucine zipper transcription factors

Site-directed mutagenesis was used to identify cis-acting elements that control hormonal and abscission-specific expression of the bean (Phaseolus vulgaris) abscission cellulase (BAC) promoter. Auxin inhibition of BAC promoter expression is at least in part controlled by a negatively regulated element and ethylene induction by a positively regulated element. One of a series of 15 different 10-bp mutations created in a 2.9-kb BAC promoter reduced reporter gene expression by 60%. The native sequence for this 10-bp mutation includes a TGA-type basic leucine zipper (bZIP) motif. Tandem ligation of three 18-bp BAC elements (Z-BAC), which includes the bZIP motif to a minimal -50 35S cauliflower mosaic virus promoter, enhanced expression in abscission zones (AZs) 13-fold over that of the minimal promoter alone. The native forward orientation of the Z-BAC elements was essential for high expression levels. Expression of the Z-BAC minimal construct was 3-fold greater in AZ than stems when compared with the expression levels of an internal control with an enhanced 35S cauliflower mosaic virus promoter. Polymerase chain reaction was used to identify three TGA-type bZIP transcription factors in an AZ cDNA library. One of these factors was of the class I type and two of the class II type. RNA-blot analysis was completed for these genes and electrophoretic mobility shift assays used to confirm their binding to the Z-BAC element. Electrophoretic mobility shift assay-binding affinity was greatest for the class I TGA-type bZIP factor. The results indicate a complex interaction of negative and positive regulating transcription factors that control BAC gene expression.

Promiscuity in ligand-binding: The three-dimensional structure of a Piromyces carbohydrate-binding module, CBM29-2, in complex with cello- and mannohexaose

Carbohydrate-protein recognition is central to many biological processes. Enzymes that act on polysaccharide substrates frequently contain noncatalytic domains, "carbohydrate-binding modules" (CBMs), that target the enzyme to the appropriate substrate. CBMs that recognize specific plant structural polysaccharides are often able to accommodate both the variable backbone and the side-chain decorations of heterogeneous ligands. "CBM29" modules, derived from a noncatalytic component of the Piromyces equi cellulase/hemicellulase complex, provide an example of this selective yet flexible recognition. They discriminate strongly against some polysaccharides while remaining relatively promiscuous toward both beta-1,4-linked manno- and cello-oligosaccharides. This feature may reflect preferential, but flexible, targeting toward glucomannans in the plant cell wall. The three-dimensional structure of CBM29-2 and its complexes with cello- and mannohexaose reveal a beta-jelly-roll topology, with an extended binding groove on the concave surface. The orientation of the aromatic residues complements the conformation of the target sugar polymer while accommodation of both manno- and gluco-configured oligo- and polysaccharides is conferred by virtue of the plasticity of the direct interactions from their axial and equatorial 2-hydroxyls, respectively. Such flexible ligand recognition targets the anaerobic fungal complex to a range of different components in the plant cell wall and thus plays a pivotal role in the highly efficient degradation of this composite structure by the microbial eukaryote.

Enzymatic properties of the low molecular mass endoglucanases Cel12A (EG III) and Cel45A (EG V) of Trichoderma reesei

Trichoderma reesei produces five known endoglucanases. The most studied are Cel7B (EG I) and Cel5A (EG II) which are the most abundant of the endoglucanases. We have performed a characterisation of the enzymatic properties of the less well-studied endoglucanases Cel12A (EG III), Cel45A (EG V) and the catalytic core of Cel45A. For comparison, Cel5A and Cel7B were included in the study. Adsorption studies on microcrystalline cellulose (Avicel) and phosphoric acid swollen cellulose (PASC) showed that Cel5A, Cel7B, Cel45A and Cel45Acore adsorbed to these substrates. In contrast, Cel12A adsorbed weakly to both Avicel and PASC. The products formed on Avicel, PASC and carboxymethylcellulose (CMC) were analysed. Cel7B produced glucose and cellobiose from all substrates. Cel5A and Cel12A also produced cellotriose, in addition to glucose and cellobiose, on the substrates. Cel45A showed a clearly different product pattern by having cellotetraose as the main product, with practically no glucose and cellobiose formation. The kinetic constants were determined on cellotriose, cellotetraose and cellopentaose for the enzymes. Cel12A did not hydrolyse cellotriose. The k(Cat) values for Cel12A on cellotetraose and cellopentaose were significantly lower compared with Cel5A and Cel7B. Cel7B was the only endoglucanase which rapidly hydrolysed cellotriose. Cel45Acore did not show activity on any of the three studied cello-oligosaccharides. The four endoglucanases' capacity to hydrolyse beta-glucan and glucomannan were studied. Cel12A hydrolysed beta-glucan and glucomannan slightly less compared with Cel5A and Cel7B. Cel45A was able to hydrolyse glucomannan significantly more compared with beta-glucan. The capability of Cel45A to hydrolyse glucomannan was higher than that observed for Cel12A, Cel5A and Cel7B. The results indicate that Cel45A is a glucomannanase rather than a strict endoglucanase.

Towards the mechanism of cellulose synthesis

Recent research has provided insights into how plants make cellulose - the major structural material of their cell walls and the basis of the cotton and wood fibre industries. Arabidopsis thaliana mutants impaired in cellulose production are defective in genes encoding membrane-bound glycosyltransferases, an endo-1,4-beta-glucanase and several enzymes involved in the N-glycosylation and quality-control pathways of the endoplasmic reticulum. The glycosyltransferases form the rosette terminal complexes seen in plasma membranes making cellulose. Synthesis might start by making lipoglucans, which, in turn, might form the substrate for the endo-1,4-beta-glucanase, before being elongated to form the long, crystalline microfibrils that assemble in the cell wall.

Suppression of a ripening-related endo-1,4-beta-glucanase in transgenic pepper fruit does not prevent depolymerization of cell wall polysaccharides during ripening

The function of the ripening-related endo-1,4-beta-D-glucanase (EGase) CaCel1 in fruit softening was investigated by suppression of CaCel1 gene expression in transgenic pepper (Capsicum annuum L.) plants using constitutive expression of a truncated sense CaCel1 transgene. In suppressed lines, immunodetectable CaCel1 protein and extractable CMCase activity were reduced to at or below the limit of detection in ripe mature red fruit, suggesting that in pepper ripening-related CMCase activity is the product of a single gene. However, the abundances of two mRNAs derived from the CaCel1 gene by differential transcription initiation were affected differently in suppressed lines. Accumulation of a 1.7 kb CaCel1 transcript was strongly suppressed, whereas the abundance of a 2.1 kb CaCel1 transcript was only partially reduced. This implies that the 1.7 kb mRNA is responsible for producing CaCel1 protein, while the 2.1 kb mRNA is translationally inactive, and as such is recalcitrant to co-suppression. Chelator-soluble polyuronides exhibited little or no depolymerization during ripening, but matrix glycans including xyloglucan were extensively depolymerized. Depolymerization of non-xyloglucan matrix glycans was the prominant cell wall change observed during pepper ripening. However, the lack of CaCel1 activity in suppressed fruit had no detectable effect on ripening-related matrix glycan depolymerization, which occurred at wild-type levels. Recombinant CaCel1 protein purified from a transgenic pepper line over-expressing functional CaCel1 was active against pepper matrix glycans in vitro, and showed greater activity against non-xyloglucan polysaccharides than against xyloglucan. Transgenic suppression of CaCel1 EGase activity has not identified the natural cell wall substrate for this enzyme, and shows that activities other than CaCel1 are responsible for the depolymerization of matrix glycans occurring during ripening in pepper.

Constitutive overexpression of a ripening-related pepper endo-1,4-beta-glucanase in transgenic tomato fruit does not increase xyloglucan depolymerization or fruit softening

The ripening-related pepper endo-1,4-beta-D-glucanase (EGase) CaCel1 was over-expressed in transgenic tomato plants under the control of the constitutive 35S promoter to investigate the effects on plant growth and fruit softening of high levels of a potential cell wall-degrading activity. In transgenic fruit, recombinant CaCel1 protein was associated with a high-salt putative cell wall fraction, and extractable CMCase activity was increased by up to 20-fold relative to controls. However, the effects of high levels of EGase activity on fruit cell wall metabolism were relatively small. The largest consequence observed was a decrease of up to 20% in the amount of matrix glycans in a 24% KOH-soluble fraction consisting of polysaccharides tightly bound to cellulose. This decrease was confined to polysaccharides other than xyloglucan, did not affect the size distribution of remaining molecules, and was not correlated with a corresponding increase in glycans in a 4% KOH-soluble fraction loosely bound to cellulose, suggesting that the missing polymers had been degraded to fragments small enough to be lost from the extracts. The amount of matrix glycans in the 4% KOH-soluble fraction was not substantially changed, but the size distribution showed a small relative increase in the amount of polymers in a peak eluting close to a linear dextran marker of 71 kDa. This could be due either to an increase in the amount of polymers of this size, or to a loss from the extract of other polymers present in peaks of higher molecular weight. Transgenic fruit were not softer than controls but appeared the same or slightly firmer at both green and red developmental stages, and no differences in plant vegetative growth were observed. CaCel1 did not cause depolymerization of tomato fruit xyloglucan in vivo, but differences in the amount or molecular weight profile of other matrix glycans were observed. The data suggest that degradation of a proportion of matrix glycans other than xyloglucan does not result in fruit softening, and that fruit softening is not limited by the amount of EGase activity present during ripening.

Expression of hemocyanin and digestive enzyme messenger RNAs in the hepatopancreas of the Black Tiger Shrimp Penaeus monodon

In order to define the cellular site of synthesis for hemocyanin and digestive enzymes in the decapod hepatopancreas, we studied the expression of messenger ribonucleic acids (RNAs) for these molecules in the epithelium lining hepatopancreas tubules. In situ hybridisation of gene probes for the digestive enzymes amylase, cathepsin-L, cellulase, chitinase-1 and trypsin to tissue sections of the shrimp hepatopancreas confirmed that the F-cells lining tertiary, secondary and primary ducts are the sites of synthesis for digestive enzyme messenger RNA (mRNA). The F-cells also contained mRNA for the hemocyanin gene. This finding raises important questions on the mechanism by which mature hemocyanin accumulates in the shrimp hemolymph. Our in situ hybridisation studies further showed that Penaeus monodon F-cells remain transcriptionally active for digestive enzyme mRNAs during periods of starvation.

Transcriptional activator, AoXlnR, mediates cellulose-inductive expression of the xylanolytic and cellulolytic genes inAspergillus oryzae

AoXlnR was isolated as a transcriptional activator of the major xylanase gene, xynF1, in Aspergillus oryzae. To investigate the spectrum of genes under the control of AoXlnR, expression of the xylanolytic and cellulolytic genes in an A. oryzae wild type strain, an AoxlnR disruptant and an AoXlnR overexpressed strain was analyzed by Northern blotting. AoXlnR mediated expression of at least four xylanolytic genes and four cellulolytic genes when induced by xylan and D-xylose. Moreover, AoXlnR was newly found to mediate the cellulose-inductive expression of the xylanolytic genes as well as the cellulolytic genes.