β-1,3-Glucanases and chitinases participate in the stress-related defence mechanisms that are possibly connected with modulation of arabinogalactan proteins (AGP) required for the androgenesis initiation in rye (Secale cereale L.)

This work presents the biochemical, cytochemical and molecular studies on two groups of PR proteins, β-1,3-glucanases and chitinases, and the arabinogalactan proteins (AGP) during the early stages of androgenesis induction in two breeding lines of rye (Secale cereale L.) with different androgenic potential. The process of androgenesis was initiated by tillers pre-treatments with low temperature, mannitol and/or reduced glutathione and resulted in microspores reprogramming and formation of androgenic structures what was associated with high activity of β-1,3-glucanases and chitinases. Some isoforms of β-1,3-glucanases, namely several acidic isoforms of about 26 kDa; appeared to be anther specific. Chitinases were well represented but were less variable. RT-qPCR revealed that the cold-responsive chitinase genes Chit1 and Chit2 were expressed at a lower level in the microspores and whole anthers while the cold-responsive Glu2 and Glu3 were not active. The stress pre-treatments modifications promoted the AGP accumulation. An apparent dominance of some AGP epitopes (LM2, JIM4 and JIM14) was detected in the androgenesis-responsive rye line. An abundant JIM13 epitopes in the vesicles and inner cell walls of the microspores and in the cell walls of the anther cell layers appeared to be the most specific for embryogenesis.

Structure and functional analysis of the Legionella pneumophila chitinase ChiA reveals a novel mechanism of metal-dependent mucin degradation

Chitinases are important enzymes that contribute to the generation of carbon and nitrogen from chitin, a long chain polymer of N-acetylglucosamine that is abundant in insects, fungi, invertebrates and fish. Although mammals do not produce chitin, chitinases have been identified in bacteria that are key virulence factors in severe respiratory, gastrointestinal and urinary diseases. However, it is unclear how these enzymes are able to carry out this dual function. Legionella pneumophila is the causative agent of Legionnaires' disease, an often-fatal pneumonia and its chitinase ChiA is essential for the survival of L. pneumophila in the lung. Here we report the first atomic resolution insight into the pathogenic mechanism of a bacterial chitinase. We derive an experimental model of intact ChiA and show how its N-terminal region targets ChiA to the bacterial surface after its secretion. We provide the first evidence that L. pneumophila can bind mucins on its surface, but this is not dependent on ChiA. This demonstrates that additional peripheral mucin binding proteins are also expressed in L. pneumophila. We also show that the ChiA C-terminal chitinase domain has novel Zn2+-dependent peptidase activity against mammalian mucin-like proteins, namely MUC5AC and the C1-esterase inhibitor, and that ChiA promotes bacterial penetration of mucin gels. Our findings suggest that ChiA can facilitate passage of L. pneumophila through the alveolar mucosa, can modulate the host complement system and that ChiA may be a promising target for vaccine development.

Discovery and identification of candidate genes from the chitinase gene family for Verticillium dahliae resistance in cotton

Verticillium dahliae, a destructive and soil-borne fungal pathogen, causes massive losses in cotton yields. However, the resistance mechanism to V. dahilae in cotton is still poorly understood. Accumulating evidence indicates that chitinases are crucial hydrolytic enzymes, which attack fungal pathogens by catalyzing the fungal cell wall degradation. As a large gene family, to date, the chitinase genes (Chis) have not been systematically analyzed and effectively utilized in cotton. Here, we identified 47, 49, 92, and 116 Chis from four sequenced cotton species, diploid Gossypium raimondii (D5), G. arboreum (A2), tetraploid G. hirsutum acc. TM-1 (AD1), and G. barbadense acc. 3-79 (AD2), respectively. The orthologous genes were not one-to-one correspondence in the diploid and tetraploid cotton species, implying changes in the number of Chis in different cotton species during the evolution of Gossypium. Phylogenetic classification indicated that these Chis could be classified into six groups, with distinguishable structural characteristics. The expression patterns of Chis indicated their various expressions in different organs and tissues, and in the V. dahliae response. Silencing of Chi23, Chi32, or Chi47 in cotton significantly impaired the resistance to V. dahliae, suggesting these genes might act as positive regulators in disease resistance to V. dahliae.

Physiology of digestion and the molecular characterization of the major digestive enzymes from Periplaneta americana

Cockroaches are among the first insects to appear in the fossil record. This work is part of ongoing research on insects at critical points in the evolutionary tree to disclose evolutionary trends in the digestive characteristics of insects. A transcriptome (454 Roche platform) of the midgut of Periplanetaamericana was searched for sequences of digestive enzymes. The selected sequences were manually curated. The complete or nearly complete sequences showing all characteristic motifs and highly expressed (reads counting) had their predicted sequences checked by cloning and Sanger sequencing. There are two chitinases (lacking mucin and chitin-binding domains), one amylase, two α- and three β-glucosidases, one β-galactosidase, two aminopeptidases (none of the N-group), one chymotrypsin, 5 trypsins, and none β-glucanase. Electrophoretic and enzymological data agreed with transcriptome data in showing that there is a single β-galactosidase, two α-glucosidases, one preferring as substrate maltase and the other aryl α-glucoside, and two β-glucosidases. Chromatographic and enzymological data identified 4 trypsins, one chymotrypsin (also found in the transcriptome), and one non-identified proteinase. The major digestive trypsin is identifiable to a major P. americana allergen (Per a 10). The lack of β-glucanase expression in midguts was confirmed, thus lending support to claims that those enzymes are salivary. A salivary amylase was molecularly cloned and shown to be different from the one from the midgut. Enzyme distribution showed that most digestion occurs under the action of salivary and midgut enzymes in the foregut and anterior midgut, except the posterior terminal digestion of proteins. A counter-flux of fluid may be functional in the midgut of the cockroach to explain the low excretory rate of digestive enzymes. Ultrastructural and immunocytochemical localization data showed that amylase and trypsin are released by both merocrine and apocrine secretion mainly from gastric caeca. Finally, a discussion on Polyneoptera digestive physiology is provided.

A Chitinase Indispensable for Formation of Protoplast ofSchizophyllum communein Basidiomycete-lytic Enzyme Preparation Produced byBacillus circulansKA-304

KA-prep, a culture filtrate of Bacillus circulans KA-304 grown on a cell-wall preparation of Schizophyllum commune, has an activity to form protoplasts from S. commune mycelia. alpha-1,3-Glucanase, which was isolated from an ammonium sulfate fraction of 0-30% saturation of KA-prep, gave the protoplast-forming activity to an ammonium sulfate fraction of 30-50% saturation of KA-prep, which contained chitinase(s) and beta-glucanase(s) but was inactive in the protoplast formation. Chitinase(s) and beta-glucanase(s) in the ammonium sulfate fraction of 30-50% saturation were separated by DEAE-cellulofine A-500 column chromatography, and the protoplast-forming activity appeared when the chitinase preparation was mixed with the alpha-1,3-glucanase. The beta-glucanase preparation was not effective for the protoplast formation whereas its addition enhanced the protoplast-forming activity of the mixture of alpha-1,3-glucanase and the chitinase preparation. The chitinase preparation contained two chitinases (chitinase I and II). Chitinase I showed the protoplast-forming activity with alpha-1,3-glucanase, but chitinase II did not. Chitinase I, a monomeric protein with a molecular weight of 41,000, was active toward colloidal chitin and ethylene glycol chitin. Chitinase I produced predominantly N,N'-diacetylchitobiose and N,N',N"-triacetylchitotriose from colloidal chitin, and the enzyme was inactive to p-NP-beta-D-N-acetylglucosaminide, suggesting that it was an endo-type enzyme. The N-terminal amino acid sequence of chitinase I (A L A T P T L N V S A S S G M) had no sequential identity to those of known chitinases.

Cloning and Characterization of a Balsam Pear Class I Chitinase Gene (Mcchit1) and Its Ectopic Expression Enhances Fungal Resistance in Transgenic Plants

A balsam pear (Momordica charantia L.) chitinase (Mcchit1) was purified and sequenced at the N-terminal. The genomic and cDNA coding sequences of Mcchit1 were cloned by rapid amplification of 3' cDNA ends (3'-RACE) and the Y-shaped adaptor dependent extension (YADE) method. Sequence analysis showed that the Mcchit1 protein is a class I chitinase containing a chitin-binding domain and a catalytic domain, but no C-terminal extension. Northern blot indicated that the Mcchit1 transcription is wound-inducible. Overexpression of Mcchit1 dramatically increased intercellular and intracellular endochitinase activities, suggesting that the Mcchit1 gene encodes a secretory endochitinase. It was also found that overexpression of Mcchit1 significantly enhanced resistance to the plant pathogenic fungus Phytophthora nicotianae in transgenic N. benthamiana plants and against Verticillium wilt in transgenic cottons, indicating that the Mcchit1 gene can be a useful gene in plant engineering against fungal diseases.

Lung chitinolytic activity and chitotriosidase are elevated in chronic obstructive pulmonary disease and contribute to lung inflammation

Chronic obstructive pulmonary disease (COPD) is characterized by chronic airway inflammation and emphysematous alveolar destruction. In this study, we have investigated whether chitotriosidase (ChTRase) and acidic mammalian chitinase, two chitinases with chitinolytic activity, are selectively augmented in COPD and contribute to its pathogenesis. We found that smokers with COPD, but not asthmatics, had higher chitinolytic activity and increased levels of ChTRase in bronchoalveolar lavage, more ChTRase-positive cells in bronchial biopsies, and an elevated proportion of alveolar macrophages expressing ChTRase than smokers without COPD or never-smokers. ChTRase accounted for approximately 80% of bronchoalveolar lavage chitinolytic activity, while acidic mammalian chitinase was undetectable. Bronchoalveolar lavage chitinolytic activity and ChTRase were associated with airflow obstruction and emphysema and with the levels of interleukin (IL)-1beta, IL-8, tumor-necrosis factor (TNF)-alpha, and its type II soluble receptor. Tumor necrosis factor-alpha stimulated ChTRase release only from alveolar macrophages from smokers with COPD, and exposure of these cells to ChTRase promoted the release of IL-8, monocyte-chemoattractant protein-1, and metalloproteinase-9. Finally, ChTRase overexpression in the lung of normal mice promoted macrophage recruitment and the synthesis of the murine homologue of IL-8, keratinocyte-derived cytokine, and of monocyte-chemoattractant protein-1. We conclude that pulmonary ChTRase overexpression may represent a novel important mechanism involved in COPD onset and progression.

Defense-related gene expression and enzyme activities in transgenic cotton plants expressing an endochitinase gene from Trichoderma virens in response to interaction with Rhizoctonia solani

There are many reports on obtaining disease-resistance trait in plants by overexpressing genes from diverse organisms that encode chitinolytic enzymes. Current study represents an attempt to dissect the mechanism underlying the resistance to Rhizoctonia solani in cotton plants expressing an endochitinase gene from Trichoderma virens. Several assays were developed that provided a powerful demonstration of the disease protection obtained in the transgenic cotton plants. Transgene-dependent endochitinase activity was confirmed in various tissues and in the medium surrounding the roots of transformants. Biochemical and molecular analyses conducted on the transgenic plants showed rapid/greater induction of ROS, expression of several defense-related genes, and activation of some PR enzymes and the terpenoid pathway. Interestingly, even in the absence of a challenge from the pathogen, the basal activities of some of the defense-related genes and enzymes were higher in the endochitinase-expressing cotton plants. This elevated defensive state of the transformants may act synergistically with the potent, transgene-encoded endochitinase activity to confer a strong resistance to R. solani infection.

Enhanced resistance to Botrytis cinerea mediated by the transgenic expression of the chitinase gene ch5B in strawberry

Plants of strawberry (cultivar Pájaro) were transformed with three defense related genes: ch5B, gln2 and ap24 using Agrobacterium tumefaciens. The ch5B gene encodes for a chitinase from Phaseolus vulgaris, while gln2 and ap24 encode for a glucanase and a thaumatin-like protein, respectively, both from Nicotiana tabacum. Sixteen transgenic lines expressing one or a combination of two defense genes were obtained. Phytopathological tests showed that two transgenic lines expressing only the ch5B gene displayed high levels of resistance to gray mold disease (Botrytis cinerea). The resistance was correlated with the presence of the foreign protein CH5B and the increase of chitinolytic activity in leaves. However, resistance toward Colletotrichum acutatum, the etiological agent of the anthracnose disease, was not enhanced in the transgenic plants. These results suggest that the ch5B gene can be used to introduce transgene-mediated resistance to gray mold in strawberry, due to the lack of natural resistance to this disease in the crop.

Abundant class III acidic chitinase homologue in tamarind (Tamarindus indica) seed serves as the major storage protein

The phyla Leguminosae contains protease inhibitors, lectins, chitinases, and glycohydrolases as major defense proteins in their seeds. Electrophoretic analysis of the seed proteins of tamarind ( Tamarindus indica L.), an agri-waste material, indicated the unusual presence of two major proteins comparable to overexpression of recombinant proteins. These proteins were identified by amino-terminal analysis to be (1) Kunitz-type trypsin inhibitor and (2) class III endochitinase (34000 Da). These two proteins were purified to apparent homogeneity by a single-step chitin bead affinity chromatography and characterized. The Kunitz inhibitor was specific toward inhibiting trypsin with a stoichiometry of 1:1. The 33000 +/- 1000 Da protein, accounting for >50% of the total seed protein, is an acidic glycoprotein exhibiting a very low endotype hydrolytic activity toward chitin derivatives. SDS-PAGE followed by densitometry of tamarind seed germination indicates the disappearance of the chitinase with the concomitant appearance of a cysteine endopeptidase. On the basis of its abundance, accumulation without any pathogenesis-related stimulus, temporal regulation, amino acid composition, and very low enzyme activity, this 34000 Da protein designated "tamarinin" physiologically serves as the major storage protein.

Role of chitinase and beta-1,3-glucanase activities produced by a fluorescent pseudomonad and in vitro inhibition of Phytophthora capsici and Rhizoctonia solani

A study was conducted to investigate the possibility of involvement of chitinase and beta-1,3-glucanase of an antagonistic fluorescent Pseudomonas in growth suppression of phytopathogenic fungi, Phytophthora capsici and Rhizoctonia solani. Fluorescent Pseudomonas isolates GRC(3) and GRC(4) were screened for their antifungal potential against phytopathogenic fungi by using dual culture technique both on solid and liquid media. The percent inhibition was calculated. Various parameters were monitored for optimization of enzyme activities by fluorescent Pseudomonas GRC(3). The involvement of chitinases, beta-1,3-glucanases, and antifungal metabolites of nonenzymatic nature was correlated with the inhibition of P. capsici and R. solani. The results provide evidence for antibiosis as a mechanism for antagonism. The study also confirms that multiple mechanisms are involved in suppressing phytopathogens as evidenced by the involvement of chitinase and beta-1,3-glucanase in inhibition of R. solani but not P. capsici by isolate GRC3.

Role of mammalian chitinases in inflammatory conditions

It has been hypothesized that dysregulated host/microbial interactions play a pivotal role in the pathogenesis of inflammatory bowel disease. However, the exact mechanisms underlying the induction and perpetuation of the intestinal disorder are unclear. Recently, we unexpectedly discovered significantly upregulated gene expression of chitinase 3-like-1 in inflamed colon of the dextran sulfate sodium-induced colitis model by employing the DNA-microarray analysis. Chitinase 3-like-1 has a chitin binding ability, but lacks the enzymatic activity of lysing microbial cell wall. Chitinase 3-like-1 protein is mainly expressed in colonic epithelial cells and macrophages in the inflamed colon of dextran sulfate sodium-induced colitis. Chitinase 3-like-1, which can be upregulated after pro-inflammatory cytokine stimulation, possesses an ability to enhance the adhesion and internalization of intracellular bacteria into colonic epithelial cells. Most importantly, in vivo neutralization of chitinase 3-like-1 significantly suppressed the development of dextran sulfate sodium-induced colitis by dramatically decreasing the bacterial adhesion and invasion into colonic epithelial cells. Furthermore, anti-chitinase 3-like-1 antibody-treated mice exhibited a significantly lower load of Salmonella typhimurium in peripheral organs as compared to control rabbit IgG-treated mice. Recently, it has been reported that acidic mammalian chitinase is expressed in the setting of T helper-2-associated inflammation and subsequently induces airway hyperresponsiveness in allergic asthma patients. In addition, pan-chitinase inhibitor significantly ameliorates T helper-2-mediated inflammation and airway hypersensitivity. These studies provide to be a novel insight into the physiological role of mammalian chitinases in host/microbial interactions, and inhibition of chitinase activity would be considered a novel therapeutic strategy of allergic and inflammatory disorders.

Characterization of a chitinolytic enzyme from Serratia sp. KCK isolated from kimchi juice

The novel chitinolytic bacterium Serratia sp. KCK, which was isolated from kimchi juice, produced chitinase A. The gene coding for the chitinolytic enzyme was cloned on the basis of sequencing of internal peptides, homology search, and design of degenerated primers. The cloned open reading frame of chiA encodes for deduced polypeptide of 563 amino acid residues with a calculated molecular mass of 61 kDa and appears to correspond to a molecular mass of about 57 kDa, which excluded the signal sequence. The deduced amino acid sequence showed high similarity to those of bacterial chitinases classified as family 18 of glycosyl hydrolases. The chitinase A is an exochitinase and exhibits a greater pH range (5.0-10.0), thermostability with a temperature optimum of 40 degrees C, and substrate range other than Serratia chitinases thus far described. These results suggested that Serratia sp. KCK chitinase A can be used for biotechnological applications with good potential.

Conserved cis-Acting Elements Upstream of Genes Composing the Chitinolytic System of Streptomycetes Are DasR-Responsive Elements

For soil-dwelling bacteria that usually live in a carbon-rich and nitrogen-poor environment, the ability to utilize chitin - the second most abundant polysaccharide on earth - is a decisive evolving advantage as it is a source for both elements. Streptomycetes are high-GC Gram-positive soil bacteria that are equipped with a broad arsenal of chitinase-degrading genes. These genes are induced when the streptomycetes sense the presence of chitooligosaccharides. Their expression is repressed as soon as more readily assimilated carbon sources become available. This includes for example glucose or N-acetylglucosamine, the monomer subunit of chitin. Historically, the first cis-acting elements involved in carbon regulation in streptomycetes were found more than a decade ago upstream of chitinase genes, but the transcriptional regulator had so far remained undiscovered. In this work, we show that these cis-acting elements consist of inverted repeats with multiple occurrences and are bound by the HutC/GntR type regulator DasR. We have therefore designated these sites as DasR-responsive elements (dre). DasR, which is also the repressor of the genes for the N-acetylglucosamine-specific phosphotransferase transport system, should therefore play a critical role in sensing the balance between the monomeric and polymeric forms of N-acetylglucosamine.

A chitinase gene, chiB, involved in the autolytic process of Aspergillus nidulans

Chitinases are thought to be involved in the morphogenesis and autolysis of filamentous fungi. We cloned a gene (chiB) encoding a class V chitinase from Aspergillus nidulans. ChiB expressed in Escherichia coli had chitin-hydrolyzing activity, indicating that chiB encoded a chitinase. Deletion of chiB affected neither germination efficiency nor hyphal growth rate, but considerably reduced the intracellular and extracellular chitinase activities. The decrease in hyphal dry weight during autolytic phase was slower in the mutant than in the wild-type strain. Western blot analysis indicated that the quantity of ChiB significantly increased when the wild-type mycelia were starved for carbon sources, a condition that induced hyphal autolysis. These results suggest that chiB plays an important role in the autolytic process in A. nidulans.

Over-expression of a cacao class I chitinase gene in Theobroma cacao L. enhances resistance against the pathogen, Colletotrichum gloeosporioides

Theobroma cacao L. plants over-expressing a cacao class I chitinase gene (TcChi1) under the control of a modified CaMV-35S promoter were obtained by Agrobacterium-mediated transformation of somatic embryo cotyledons. Southern blot analysis confirmed insertion of the transgene in eight independent lines. High levels of TcChi1 transgene expression in the transgenic lines were confirmed by northern blot analysis. Chitinase activity levels were measured using an in vitro fluorometric assay. The transgene was expressed at varying levels in the different transgenic lines with up to a sixfold increase of endochitinase activity compared to non-transgenic and transgenic control plants. The in vivo antifungal activity of the transgene against the foliar pathogen Colletotrichum gloeosporioides was evaluated using a cacao leaf disk bioassay. The assay demonstrated that the TcChi1 transgenic cacao leaves significantly inhibited the growth of the fungus and the development of leaf necrosis compared to controls when leaves were wound inoculated with 5,000 spores. These results demonstrate for the first time the utility of the cacao transformation system as a tool for gene functional analysis and the potential utility of the cacao chitinase gene for increasing fungal pathogen resistance in cacao.

Review of fungal chitinases

Chitin is the second most abundant organic and renewable source in nature, after cellulose. Chitinases are chitin-degrading enzymes. Chitinases have important biophysiological functions and immense potential applications. In recent years, researches on fungal chitinases have made fast progress, especially in molecular levels. Therefore, the present review will focus on recent advances of fungal chitinases, containing their nomenclature and assays, purification and characterization, molecular cloning and expression, family and structure, regulation, and function and application.

The phylogenetically conserved molluscan chitinase-like protein 1 (Cg-Clp1), homologue of human HC-gp39, stimulates proliferation and regulates synthesis of extracellular matrix components of mammalian chondrocytes

Members of chitinase-like proteins (CLPs) have attracted much attention because of their ability to promote cell proliferation in insects (imaginal disc growth factors) and mammals (YKL-40). To gain insights into the molecular processes underlying the physiological control of growth and development in Lophotrochozoa, we report here the cloning and biochemical characterization of the first Lophotrochozoan CLP from the oyster Crassostrea gigas (Cg-Clp1). Gene expression profiles monitored by real time quantitative reverse transcription-PCR in different adult tissues and during development support the involvement of this protein in the control of growth and development in C. gigas. Recombinant Cg-Clp1 demonstrates a strong affinity for chitin but no chitinolytic activity, as was described for the HC-gp39 mammalian homolog. Furthermore, transient expression of Cg-Clp1 in primary cultures of rabbit articular chondrocytes as well as the use of both purified recombinant protein and conditioned medium from Cg-Clp1-expressing rabbit articular chondrocytes established that Cg-Clp1 stimulates cell proliferation and regulates extracellular matrix component synthesis, showing for the first time a possible involvement of a CLP on type II collagen synthesis regulation. These observations together with the fact that Cg-Clp1 gene organization strongly resembles that of its mammalian homologues argue for an early evolutionary origin and a high conservation of this class of proteins at both the structural and functional levels.

Promoter activation of pepper class II basic chitinase gene, CAChi2, and enhanced bacterial disease resistance and osmotic stress tolerance in the CAChi2-overexpressing Arabidopsis

The activation of the CAChi2 promoter as the result of bacterial infection and osmotic stresses was examined using the Agrobacterium-mediated transient expression assay. Several stress-related cis-acting elements were revealed within the upstream genomic sequence of the CAChi2 gene. In tobacco leaf tissues transiently transformed with the CAChi2 promoter-beta-glucuronidase (GUS) gene, the CAChi2 promoter was up-regulated by Pseudomonas syringae pv. tabaci infection. The CAChi2-GUS activation was closely related to osmotic stresses, including treatment with mannitol and NaCl. The -378 CAChi2 promoter was sufficient for the CAChi2 gene induction by salicylic acid treatment. CAChi2 overexpression in the transgenic Arabidopsis plants enhanced bacterial disease resistance against Pseudomonas syringae pv. tomato infection. CAChi2-overexpressing Arabidopsis plants also exhibited increased tolerance to NaCl-induced osmotic stresses during seed germination and seedling growth. CAChi2 overexpression induced the expression of the NaCl stress-responsive gene RD29A in the absence of NaCl stress. The CAChi2-overexpressing transgenic plants exhibited increased sensitivity to abscisic acid during seed germination.

An agglutinating chitinase with two chitin-binding domains confers fungal protection in transgenic potato

Brassica juncea BjCHI1 is a unique chitinase with two chitin-binding domains. Here, we show that, unlike other chitinases, potato-expressed BjCHI1 shows hemagglutination ability. BjCHI1 expression in B. juncea seedlings is induced by Rhizoctonia solani infection, suggesting its protective role against this fungus. To verify this, transgenic potato (Solanum tuberosum L. cv. Desiree) plants expressing BjCHI1 generated by Agrobacterium-mediated transformation were challenged with R. solani. We also transformed potato with a cDNA encoding Hevea brasiliensis beta-1,3-glucanase, designated HbGLU, and a pBI121-derivative that contains cDNAs encoding both BjCHI1 and HbGLU. In vitro fungal bioassays using Trichoderma viride showed that extracts from transgenic potato lines co-expressing BjCHI1 and HbGLU inhibited fungal growth better than extracts from transgenic potato expressing either BjCHI1 or HbGLU, suggesting a synergistic effect. Consistently, in vivo fungal bioassays with soil-borne R. solani on young transgenic potato plants indicated that the co-expressing plants showed healthier root development than untransformed plants or those that expressed either BjCHI1 or HbGLU. Light microscopy and transmission electron microscopy revealed abundant intact R. solani hyphae and monilioid cells in untransformed roots and disintegrated fungus in the BjCHI1-expressing and the BjCHI1 and HbGLU co-expressing plants. Observations of collapsed epidermal cells in the co-expressing potato roots suggest that these proteins effectively degrade the fungal cell wall, producing elicitors that initiate other defense responses causing epidermal cell collapse that ultimately restricts further fungal penetration.

Cloning, expression and functional characterisation of chitinase from larvae of tomato moth (Lacanobia oleracea): a demonstration of the insecticidal activity of insect chitinase

Chitinases are vital to moulting in insects, and may also affect gut physiology through their involvement in peritrophic membrane turnover. A cDNA encoding chitinase was cloned from larvae of tomato moth (Lacanobia oleracea), a Lepidopteran pest of crops. The predicted protein contains 553 amino acid residues, with a signal peptide of 20 a.a. Sequence comparison showed 75-80% identity with other Lepidopteran chitinases. L. oleracea chitinase was produced as a functional recombinant enzyme in the yeast Pichia pastoris. A fusion protein containing chitinase joined to the N-terminus of snowdrop lectin (GNA) was also produced, to determine whether GNA could deliver chitinase to the haemolymph of Lepidopteran larvae after oral ingestion. The purified recombinant proteins exhibited similar levels of chitinase activity in vitro. Both proteins were highly toxic to L. oleracea larvae on injection, causing 100% mortality at low dose (2.5 microg/g insect). Injection of chitinase prior to the moult resulted in decreased cuticle thickness. The recombinant proteins caused chronic effects when fed, causing reductions in larval growth and food consumption by up to 60%. The oral toxicity of chitinase was not increased by attaching GNA in the fusion protein, due to degradation in the larval gut, preventing GNA acting as a "carrier".

A putative double role of a chitinase in a cnidarian: pattern formation and immunity

Chitinases are enzymes that degrade chitin, the second most abundant polymer in nature. They are ubiquitous among living organisms where they play a role in development, food-digestion and innate immunity. We have cloned and characterized the first cnidarian chitinase cDNA from the hydroid Hydractinia. The Hydractinia chitinase exhibits a typical secreted family 18 hydrolases primary structure. In situ hybridization and RT-PCR experiments showed that it is exclusively expressed in ectodermal tissues of the animal, only following metamorphosis while undetectable in embryonic and larval stages. Most prominent expression was observed in the stolonal compartment of colonies, structures that are covered by a chitinous periderm. Chitinase mRNA was detected in new branching points along stolons and in hyperplastic stolons indicating a role of the enzyme in pattern formation and allorecognition. It was also expressed in polyps where it was mostly restricted to their basal portion. This expression pattern suggests that HyChit1 also fulfills a role in host defense, probably against fungal and nematode pathogens. Endodermal expression of HyChit1 has never been observed, suggesting that the enzyme does not participate in food-digestion.

Molecular characterization of a pathogenesis-related protein 8 gene encoding a class III chitinase in rice

A cDNA encoding a class III chitinase (Oschib1) was isolated from a cDNA library constructed from rice leaves infected with the blast fungus Magnaporthe grisea. The cDNA contains an open reading frame of 861 nucleotides encoding 286 amino acid residues with a pI of 5.06. The deduced amino acid sequence of Oschibl has a high level of similarity with class IIIb chitinases of Gladiolus gandavensis (46%) and Tulipa bakeri (49%). A high level of Oschibl mRNA was detected after inoculation with M. grisea or Xanthomonas oryzae pv. oryzae. Expression of Oschib1 was induced more rapidly when an avirulent strain of M. grisea was inoculated (incompatible interaction) than when a virulent strain was used (compatible interaction). Expression of Oschibl was also induced by treatment of signaling molecules such as salicylic acid, ethylene, and methyl jasmonic acid, and by treatment with H2O2 or CuSO4. The induction patterns of Oschibl expression suggest that Oschib1 may be involved in defense response against pathogen infections and may be classified as a member of pathogenesis-related protein 8 in rice.

Disruption of the gene encoding the ChiB1 chitinase of Aspergillus fumigatus and characterization of a recombinant gene product

The gene encoding a major, inducible 45 kDa chitinase of Aspergillus fumigatus was cloned and analysis of the deduced amino acid sequence identified a chitinase of the fungal/bacterial class which was designated ChiB1. Recombinant ChiB1, expressed in Pichia pastoris, was shown to function by a retaining mechanism of action. That is, the beta-conformation of the chitin substrate linkage was preserved in the product in a manner typical of family 18 chitinases. Cleavage patterns with the N-acetylglucosamine (GlcNAc) oligosaccharide substrates GlcNAc(4), GlcNAc(5) and GlcNAc(6) indicated that the predominant reaction involved hydrolysis of GlcNAc(2) from the non-reducing end of each substrate. Products of transglycosylation were also identified in each incubation. Following disruption of chiB1 by gene replacement, growth and morphology of disruptants and of the wild-type strain were essentially identical. However, during the autolytic phase of batch cultures the level of chitinase activity in culture filtrate from a disruptant was much lower than the activity from the wild-type. The search for chitinases with morphogenetic roles in filamentous fungi should perhaps focus on chitinases of the fungal/plant class although such an investigation will be complicated by the identification of at least 11 putative active site domains for family 18 chitinases in the A. fumigatus TIGR database (http://www.tigr.org/).

[BjCHI1 from Brassica juncea displays both chitinase and agglutination activity]

The proteins encoded by the Brassica juncea chitinase gene BjCHI1 and its derived genes BjCHI2 and BjCHI3 were expressed by Multi-copy Pichia expression system. The chitinase activity of FPLC purified BjCHI1, BjCHI2 and BjCHI3 were tested and the results showed that all the three proteins degraded both CM-chitin-RBV and colloidal chitin. The Km values of BjCHI1, BjCHI2 and BjCHI3 for CM-chitin-RBV were estimated as 0.799 mg/mL, 0.544 mg/mL and 0.793 mg/mL, respectively. When the colloidal chitin was used as substrate, the Km values were 0.281 mg/mL, 0.388 mg/mL and 1.643 mg/mL, respectively, indicating chitin-binding domain can increase affinity of chitinase to insoluble substrate. In the agglutination activity assay, only BjCHI1 shows activity when the protein concentration was more than 33 micrograms/mL, while BjCHI2 and BjCHI3 without agglutination activity even when the concentration was increased as high as 800 micrograms/mL. This means that the two chitin-binding domains in BjCHI1 are essential for agglutination and BjCHI1 is the first protein which shows both chitinase and agglutination activity identified so far in plants.

The chitinase 3-like protein human cartilage glycoprotein 39 (HC-gp39) stimulates proliferation of human connective-tissue cells and activates both extracellular signal-regulated kinase- and protein kinase B-mediated signalling pathways

Human cartilage glycoprotein 39 (HC-gp39) is a glycoprotein secreted by articular chondrocytes, synoviocytes and macrophages. Increased levels of HC-gp39 have been demonstrated in synovial fluids of patients with rheumatoid or osteoarthritis. The increased secretion of HC-gp39 under physiological and pathological conditions with elevated connective-tissue turnover suggests its involvement in the homoeostasis of these tissues. We report here that HC-gp39 promotes the growth of human synovial cells as well as skin and fetal lung fibroblasts. A dose-dependent growth stimulation was observed when each of the fibroblastic cell lines was exposed to HC-gp39 in a concentration range from 0.1 to 2 nM, which is similar to the effective dose of the well-characterized mitogen, insulin-like growth factor-1. At suboptimal concentrations, the two growth factors work in a synergistic fashion. The use of selective inhibitors of the mitogen-activated protein kinase and the protein kinase B (AKT) signalling pathways indicates that both are involved in mediating the mitogenic response to HC-gp39. Phosphorylation of both extracellular signal-regulated kinases 1/2 and AKT occurred in a dose- and time-dependent fashion upon addition of HC-gp39. Activation of these signalling pathways could also be demonstrated in human chondrocytes. Thus HC-gp39 initiates a signalling cascade in connective-tissue cells which leads to increased cell proliferation, suggesting that this protein could play a major role in the pathological conditions leading to tissue fibrosis.

Mark-release-recapture of sand flies fed on leishmanial dogs: the natural life-cycle of Leishmania infantum in Phlebotomus ariasi

Wild-caught Phlebotomus ariasi Tonnoir permitted to feed on dogs infected with Leishmania infantum Nicolle were marked with fluorescent powder and released into their natural habitat in an uninhabited area of the Cévennes in southern France. Over a period of 29 days after release, 253 females were recaptured with CDC miniature light traps or by active search at night with portable UV lamps. The ovaries and infections in the alimentary tract were then examined. The females oviposited 6 nights after in infecting blood meal. Second blood meals were never taken during the maturation of eggs. During the first ovarian cycle, midgut infections with promastigotes were only moderately heavy. The intensity of infection increased markedly during the second ovarian cycle and, in the third ovarian cycle, the first pharynx infected with paramastigotes was seen (on day 19). From day 19 to day 29, 76% of the flies had pharyngeal infections. Three out of 19 sand flies with pharyngeal infections recaptured during this period had metacyclic promastigotes in their mouthparts. The long time required for parasites to reach the proboscis in completely natural conditions suggests that their presence in the mouthparts is not a prerequisite for transmission by bite. It is more likely that transmission is most commonly by the regurgitation of metacyclic promastigotes from the thoracic midgut following damage to the stomodaeal valve by chitinase produced by the parasite during its development in the gut of the fly. Nevertheless, it is reasonable to assume that the bite of a fly with metacyclic promastigotes in the proboscis (or salivary glands) would also be infective.

The extracellular transport signal of the Vibrio cholerae endochitinase (ChiA) is a structural motif located between amino acids 75 and 555

ChiA, an 88-kDa endochitinase encoded by the chiA gene of the gram-negative enteropathogen Vibrio cholerae, is secreted via the eps-encoded main terminal branch of the general secretory pathway (GSP), a mechanism which also transports cholera toxin. To localize the extracellular transport signal of ChiA that initiates transport of the protein through the GSP, a chimera comprised of ChiA fused at the N terminus with the maltose-binding protein (MalE) of Escherichia coli and fused at the C terminus with a 13-amino-acid epitope tag (E-tag) was expressed in strain 569B(chiA::Kan(r)), a chiA-deficient but secretion-competent mutant of V. cholerae. Fractionation studies revealed that blockage of the natural N terminus and C terminus of ChiA did not prevent secretion of the MalE-ChiA-E-tag chimera. To locate the amino acid sequences which encoded the transport signal, a series of truncations of ChiA were engineered. Secretion of the mutant polypeptides was curtailed only when ChiA was deleted from the N terminus beyond amino acid position 75 or from the C terminus beyond amino acid 555. A mutant ChiA comprised of only those amino acids was secreted by wild-type V. cholerae but not by an epsD mutant, establishing that amino acids 75 to 555 independently harbored sufficient structural information to promote secretion by the GSP of V. cholerae. Cys77 and Cys537, two cysteines located just within the termini of ChiA(75-555), were not required for secretion, indicating that those residues were not essential for maintaining the functional activity of the ChiA extracellular transport signal.

What is the role of the hevein-like domain of fruit class I chitinases in their allergenic capacity?

BACKGROUND

Class I chitinases are the major panallergens in fruits associated with the latex-fruit syndrome. These enzymes contain an N-terminal hevein-like domain homologous to latex hevein, and a larger catalytic domain. The role of these domains in their allergenic capacity is still controversial.

OBJECTIVE

We sought to evaluate the role of both domains of class I chitinases in their IgE-binding properties, using Cas s 5, the major allergen from chestnut, as a model.

METHODS

Recombinant Cas s 5 and its deleted form, lacking the hevein-like domain, designated rCat, were expressed in Pichia pastoris using the pPIC 9 vector. Both recombinant products were purified from the supernatants of transformed yeast cultures by gel-filtration and cation-exchange chromatography. The isolated proteins were characterized by N-terminal sequencing, enzymatic activity and N-glycosylation tests, anti-chitinase and specific IgE immunodetection. Immunoblot, RAST and CAP inhibition assays were also performed.

RESULTS

Both purified rCas s 5 and rCat showed the expected N-terminal amino acid sequences and an enzymatic activity similar to that of their natural counterparts isolated from chestnut seeds, and were strongly recognized by anti-chitinase antibodies. In contrast, only rCas s 5, but not rCat, bound specific IgE from sera of patients suffering from the latex-fruit syndrome, and fully inhibited IgE-binding to natural Cas s 5 in immunoblot inhibition assays. Latex hevein also exerted a strong immunoblot inhibition of IgE-binding to chestnut Cas s 5. RAST and CAP inhibition using whole chestnut extract on the solid phase, rendered inhibition levels around 70-90% for rCas s 5 and 60% for rCat, in contrast to the immunoblotting results.

CONCLUSIONS

Recombinant Cas s 5 behaves like natural Cas s 5 in IgE-binding assays in vitro. The hevein-like domain of allergenic class I chitinases seems to include all their main IgE-binding epitopes when tested by immunodetection and immunoblot inhibition experiments. RAST and CAP inhibition assays, on the contrary, suggest that relevant epitopes are also harboured in the catalytic domain of these allergens.

The biological function of sand fly and Leishmania glycosidases

This is a summary of the recent work on some glycosidases of sand flies and their Leishmania parasites. Glycosidases catalyze the hydrolysis of complex sugar subunits of polysaccharides into simple sugars. Leishmania major parasites secrete chitinase and N-acetylglucosaminase, which enables them to survive in the gut of the sand fly and are important in facilitating their transmission by the phlebotomine sand fly Phlebotomus papatasi. These enzymes are found in a wide range of trypanosomatids and the gene locus is highly conserved. The sand flies feed on plants and the ingested tissues may contain cellulose particles that the sand flies are unable to digest. Cellulolytic enzymes are secreted by L. major promastigotes and this may help to break down cellulose in infected flies and sustain their growth. Starch is a main photosynthesis product that is stored in leaves. Starch grains have been found in the midguts of field caught sand flies and alpha-amylase, the specific enzyme for starch, has been found in the salivary glands and other organs of Lutzomyia longipalpis and P. papatasi. Alpha-amylase and alpha-glucosidase are expressed by L. major promastigotes and alpha-glucosidase is secreted by several trypanosomatid genera, but not by all those examined. Primers originally designed to amplify P. papatasi amylase DNA sequences, by polymerase chain reaction (PCR), also amplified DNA from all Old World Leishmania species, indicating that the gene is highly conserved between sand flies and these parasites.

Characterization of a chitinase and an endo-beta-1,3-glucanase from Trichoderma harzianum Rifai T24 involved in control of the phytopathogen Sclerotium rolfsii

Of 24 Trichoderma isolates, T harzianum Rifai (T24) showed a potential for control of the phytopathogenic basidiomycete Sclerotium rolfsii. When T24 was grown on different carbon sources, growth inhibition of S. rolfsii by the T24 culture filtrate correlated with the activity of extracellular chitinase and beta-1,3-glucanase. The 43-kilodalton (kDa) chitinase and the 74-kDa beta-1,3-glucanase were purified from the T24 culture filtrate in two and three steps, respectively, using ammonium sulphate precipitation followed by hydrophobic interaction chromatography (phenyl-Sepharose) and gel filtration (beta-1,3-glucanase). Km and Kcat were 3.8 g l(-1) and 0.71 s(-1) for the chitinase (chitin) and 1.1 g(-1) and 52 s(-1) for the beta-1,3-glucanase (laminarin). The chitinase showed higher activity on chitin than on less-acetylated substrate analogues (chitosan), while the beta-1,3-glucanase was specific for beta-1,3-linkages in polysaccharides. Both enzymes were stable at 30 degrees C, while at 60 degrees C the chitinase and the beta-1,3-glucanase were rapidly inactivated, showing half-lives of 15 and 20 min, respectively. The enzymes inhibited growth of S. rolfsii in an additive manner showing a promising ED50 (50% effective dose) value of 2.7 microg/ml.

Production of 6-methylsalicylic acid by expression of a fungal polyketide synthase activates disease resistance in tobacco

Salicylic acid (SA) has been shown to act as a signal molecule that is produced by many plants subsequent to the recognition of potentially pathogenic microbes. Increases in levels of SA often trigger the activation of plant defenses and can result in increased resistance to subsequent challenge by pathogens. We observed that the polyketide 6-methylsalicylic acid (6-MeSA), a compound that apparently is not endogenous to tobacco, can mimic SA. Tobacco leaves treated with 6-MeSA show enhanced accumulation of the pathogenesis-related (PR) proteins PR1, beta-1,3-glucanase, and chitinase and also develop increased resistance to tobacco mosaic virus. We transformed tobacco with 6msas, the 6-methylsalicylic acid synthase (6MSAS) gene from Penicillium patulum, to generate plants that constitutively accumulate 6-MeSA. Analysis of primary transformants and the first generation progeny of 6MSAS tobacco revealed that plants can be engineered to accumulate significant amounts of 6-MeSA as a conjugate. Levels of total 6-MeSA increased with plant age. Increased 6-MeSA accumulation correlated with increased levels of PR1 and chitinase proteins and resulted in enhanced resistance of NN genotype 6MSAS tobacco to tobacco mosaic virus. Our results demonstrate that a multistep biosynthetic pathway can be engineered into plants using a single fungal polyketide synthase gene. The functional expression of 6msas can be used to activate disease resistance pathways that normally are induced by SA.

Disruption of the gene which encodes a serodiagnostic antigen and chitinase of the human fungal pathogen Coccidioides immitis

Disruption of genes in medically important fungi has proved to be a powerful tool for evaluation of putative virulence factors and identification of potential protein targets for novel antifungal drugs. Chitinase has been suggested to play a pivotal role in autolysis of the parasitic cell wall of Coccidioides immitis during the asexual reproductive cycle (endosporulation) of this systemic pathogen. Two chitinase genes (CTS1 and CTS2) of C. immitis have been cloned. Preliminary evidence has suggested that expression of CTS1 is markedly increased during endospore formation. The secreted CTS1 chitinase has also been shown to react with patient anti-Coccidioides complement-fixing (CF) antibody and is a valuable aid in the serodiagnosis of coccidioidomycosis. To examine the role of CTS1 in the morphogenesis of parasitic cells, the CTS1 gene was disrupted by a single, locus-specific crossover event. This resulted in homologous integration of a pAN7.1 plasmid construct that contained a 1.1-kb fragment of the chitinase gene into the chromosomal DNA of C. immitis. Results of Southern hybridizations, immunoblot analyses of culture filtrates using both CTS1-specific murine antiserum and serum from a patient with confirmed coccidioidal infection, an immunodiffusion test for CF antigenicity, and substrate gel electrophoresis assays of chitinase activity confirmed that the CTS1 gene was disrupted and nonfunctional. This is the first report of a successful targeted gene disruption in C. immitis. However, loss of CTS1 function had no effect on virulence or endosporulation. Comparative assays of chitinase activity in the parental and Deltacts1 strains suggested that the absence of a functional CTS1 gene can be compensated for by elevated expression of the CTS2 gene. Current investigations are focused on disruption of CTS2 in the Deltacts1 host to further evaluate the significance of chitinase activity in the parasitic cycle of C. immitis.

Chitinases in biological control

The public concern over the harmful effects of chemical pesticides on the environment and human health has enhanced the search for safer, environmentally friendly control alternatives. Control of plant pests by the application of biological agents holds great promise as an alternative to the use of chemicals. It is generally recognized that biological control agents are safer and more environmentally sound than is reliance on the use of high volumes of pesticides. Due to the importance of chitinolytic enzymes in insect, nematode, and fungal growth and development, they are receiving attention in regard to their development as biopesticides or chemical defense proteins in transgenic plants and microbial biocontrol agents. In this sense, biological control of some soil-borne fungal diseases has been correlated with chitinase production. Fungi- and bacteria-producing chitinases exhibit antagonism against fungi, and inhibition of fungal growth by plant chitinases has been demonstrated. Insect pathogenic fungi have considerable potential for the biological control of insect pests. Entomopathogenic fungi apparently overcome physical barriers of the host by producing multiple extracellular enzymes including chitinolytic enzymes, which help to penetrate the cuticle and facilitate infection. In this chapter, the role of chitinases in biological control and their potential use in the improvement of biocontrol agents and crop plants by genetic engineering is analyzed in view of recent findings.

Identification of a novel eosinophil chemotactic cytokine (ECF-L) as a chitinase family protein

A novel eosinophil chemotactic cytokine (ECF-L) was purified from the culture supernatant of splenocytes of mice by a combination of anion-exchange chromatography, Procion red-agarose affinity chromatography, size exclusion high performance liquid chromatography (HPLC), and reverse phase HPLC. The NH(2)-terminal amino acid sequence was determined by direct protein sequencing. An ECF-L cDNA clone of 1,506 nucleotides was isolated from a cDNA library, and the nucleotide sequence predicted a mature protein of 397 amino acids. A recombinant ECF-L showed a level of eosinophil chemotactic activity comparable with that of natural ECF-L, and the activity was inhibited by a monoclonal antibody to ECF-L. ECF-L also attracted T lymphocytes and bone marrow polymorphonuclear leukocytes in vitro, whereas it caused selective extravasation of eosinophils in vivo. ECF-L mRNA was highly expressed in spleen, bone marrow, lung, and heart. A comprehensive GenBank data base search revealed that ECF-L is a chitinase family protein. ECF-L retains those amino acids highly conserved among chitinase family proteins, but Asp and Glu residues essential for the proton donation in hydrolysis were replaced by Asn and Gln, respectively. Although ECF-L contains a consensus CXC sequence near the NH(2) terminus akin to chemokine family proteins, the rest of ECF-L shows poor homology with chemokines.

Involvement of chitinases of Bacillus thuringiensis during pathogenesis in insects

Bacillus thuringiensis subsp. israelensis IPS78 and B. thuringiensis subsp. aizawai HD133 both secreted exochitinase activity when grown in a medium containing chitin. Allosamidin, a specific chitinase inhibitor, inhibited activity from both strains, with IC50 values of about 50 microM with colloidal chitin as substrate and between 1 and 10 microM with 4-methylumbelliferyl-diacetylchitobioside and 4-methylumbelliferyl-triacetylchitotrioside as substrates. The involvement of these chitinolytic activities during pathogenesis in insects has been investigated with B. thuringiensis subsp. israelensis IPS78 against larvae of the midge Culicoides nubeculosus, and with B. thuringiensis subsp. aizawai HD133 against caterpillars of the cotton leafworm Spodoptera littoralis. Presence of 100 microM allosamidin increased the LD50 by factors of 1.3 and 1.4, respectively, demonstrating a role for bacterial chitinases in the attack on the insects. Presence of chitinase A from Serratia marcescens considerably decreased the values for LD50 confirming previous observations with different systems of the potentiation of entomopathogenesis of B. thuringiensis by exogenous chitinases. The most likely action of the endogenous chitinases of B. thuringiensis is to weaken the insects' peritrophic membranes, allowing more ready access of the bacterial toxins to the gut epithelia. Addition of exogenous chitinases will then increase this effect. Complementary cross-infection experiments, strain HD133 against midge larvae and strain IPS78 against caterpillars, were performed to investigate the pathogen/host specificities of the effects. Results showed that much higher concentrations of bacteria were required to achieve even low mortalities, and addition of chitinase A gave no increase in death rate.

Chitosanase from Streptomyces sp. strain N174: a comparative review of its structure and function

Novel information on the structure and function of chitosanase, which hydrolyzes the beta-1,4-glycosidic linkage of chitosan, has accumulated in recent years. The cloning of the chitosanase gene from Streptomyces sp. strain N174 and the establishment of an efficient expression system using Streptomyces lividans TK24 have contributed to these advances. Amino acid sequence comparisons of the chitosanases that have been sequenced to date revealed a significant homology in the N-terminal module. From energy minimization based on the X-ray crystal structure of Streptomyces sp. strain N174 chitosanase, the substrate binding cleft of this enzyme was estimated to be composed of six monosaccharide binding subsites. The hydrolytic reaction takes place at the center of the binding cleft with an inverting mechanism. Site-directed mutagenesis of the carboxylic amino acid residues that are conserved revealed that Glu-22 and Asp-40 are the catalytic residues. The tryptophan residues in the chitosanase do not participate directly in the substrate binding but stabilize the protein structure by interacting with hydrophobic and carboxylic side chains of the other amino acid residues. Structural and functional similarities were found between chitosanase, barley chitinase, bacteriophage T4 lysozyme, and goose egg white lysozyme, even though these proteins share no sequence similarities. This information can be helpful for the design of new chitinolytic enzymes that can be applied to carbohydrate engineering, biological control of phytopathogens, and other fields including chitinous polysaccharide degradation.

Cloning and characterization of a chitinase-encoding gene (chiA) from Aspergillus nidulans, disruption of which decreases germination frequency and hyphal growth

We cloned a chitinase-encoding gene from Aspergillus nidulans by polymerase chain reaction using degenerated oligonucleotide primers designed from the conserved amino acid sequences among chitinases from yeasts and Rhizopus spp. The cloned gene, named chiA, encoded a polypeptide consisting of 660 amino acids. Disruption of chiA had no effect on hyphal or conidiophore morphology, but germination frequency and hyphal growth rate decreased substantially. Expression of chiA was investigated using Escherichia coli beta-galactosidase as a reporter enzyme. The beta-galactosidase activity was present during hyphal growth and increased twice as the conidiophores developed. In situ staining of beta-galactosidase activity found high expression in metulae, phialides, and conidia during conidiophore development, indicating that the expression of chiA is developmentally regulated. This is the first report to isolate a chitinase gene from A. nidulans and investigate its functions using the gene disruption technique and gene fusion methods in filamentous fungi.

Secreted enzymes of Aeromonas

A hallmark characteristic of species of Aeromonas is their ability to secrete a wide variety of enzymes associated with pathogenicity and environmental adaptability. Among the most intensively studied are beta-lactamases, lipases, hemolytic enterotoxins, proteases, chitinases, nucleases and amylases. Multiple copies of genes encoding each type of enzyme provide additional biological diversity. Except for the chitinases, these multiple copies show little evolutionary relatedness at the DNA level and only limited similarity at the protein level. Indeed a number of the genes, such as nuclease H of A. hydrophila, have no similarity to known prokaryotic or eukaryotic sequences. The challenge is to determine how these genes evolved, where they originated and why Aeromonas possesses them in such abundance and variety.

Interaction of tobacco nuclear protein with an elicitor-responsive element in the promoter of a basic class I chitinase gene

The expression of tobacco class I chitinase genes is effectively induced by a fungal elicitor in suspension-cultured cells. A putative cis-acting elicitor-responsive element (EIRE) was identified previously in the promoter of the class I chitinase gene, CHN5O. To confirm that the EIRE sequence directly mediates the regulation of gene expression by the elicitor, I constructed a deleted promoter that controlled a reporter gene for beta-glucuronidase (gus) and examined expression of the construct in transgenic tobacco calli. Both expression and responsiveness to the elicitor disappeared, when the region of the promoter that included the EIRE sequence had been deleted. To define the specific sequence within the EIRE that interacts with nuclear factor(s), a gel mobility shift assay was performed with wild-type and mutated elements. Results of binding and competition experiments revealed that the nuclear factor(s) bound specifically to the sequence motif, (-534)GGTCANNNAGTC(-523), and that both of the repeated sites were involved in the binding of the nuclear factors. Moreover, the binding was influenced by the distance between the two repeated sites. In addition, the elicitor-inducible activity of the binding to this motif was reduced in nuclear extracts prepared from the cells that had been treated with cycloheximide or staurosporine.

Leaf senescence in Brassica napus: expression of genes encoding pathogenesis-related proteins

Genes that are expressed during leaf senescence in Brassica napus were identified by the isolation of representative cDNA clones. DNA sequence and deduced protein sequence from two senescence-related cDNAs, LSC94 and LSC222, representing genes that are expressed early in leaf senescence before any yellowing of the leaves is visible, showed similarities to genes for pathogenesis-related (PR) proteins: a PR-1a-like protein and a class IV chitinase, respectively. The LSC94 and LSC222 genes showed differential regulation with respect to each other; an increase in expression was detected at different times during development of healthy leaves. Expression of both genes was induced by salicylic acid treatment. These findings suggest that some PR genes, as well as being induced by pathogen infection, may have alternative functions during plant development, for example in the process of leaf senescence.

Structure and function of a family of chitinase isozymes from Brugian microfilariae

A family of chitinase isozymes, consisting of three proteins from the microfilariae of Brugia pahangi and two previously described chitinases from the microfilariae of B. malayi, has been characterized. The five members of this family display closely related chitin-degrading activities, characterized by strong endo- rather than exochitinase activity. All five proteins have highly conserved sequences at their amino-termini and appear to share a two-domain tertiary structure, as demonstrated by proteolysis of the native molecules. The amino-terminal domain appears to be responsible for the enzymatic activity and retains this activity when cleaved and separated from the remainder of the molecule(s). Glycosylation differences are apparent for the isozymes from the two different Brugian species. No representatives of this family could be detected in the microfilariae of another filarial species, Dirofilaria immitis, which differs in several aspects of its lifestyle from the Brugian filariae.

Signal molecules involved in plant embryogenesis

In plant embryogenesis, inductive interactions mediated by diffusable signal molecules are most likely of great importance. Evidence has been presented that at late globular stages in plant embryogenesis, perturbation of the polar auxin transport results in abberrant embryo morphology. Rhizobium lipooligosaccharides or Nod factors are a newly discovered class of bacterial molecules that are able to trigger initial steps in root nodule development in legumes. Part of the activity of Nod factors may be directed towards alteration of endogenous plant growth regulator balance. The same bacterial Nod factors promoted the formation of globular embryos in the carrot cell line ts11. Whether there exist plant analogues of the Nod factors and whether these molecules are active as a more universal control system perhaps designed to initiate and or mediate gradients in auxin and cytokinin remains to be determined.

Sequence of a cDNA and expression of the gene encoding epidermal and gut chitinases of Manduca sexta

Insects use chitinolytic enzymes to digest chitin in the exoskeleton during the molting process. We have isolated and sequenced a chitinase-encoding cDNA from the tobacco hornworm, Manduca sexta, compared its sequence with genes encoding chitinolytic enzymes from other sources, and studied chitinase gene expression and hormonal regulation during the larval-pupal transformation. The insert DNA in this clone is 2452 nucleotides long with an open reading frame of 1662 nucleotides that encodes a protein of 554 amino acids with a molecular weight of 62 kDa. Several regions of the amino acid sequence in this protein are similar to sequences in yeast, cucumber and bacterial endo-beta-N-acetylglucosaminidases. Hybrid-selection of mRNA and in vitro translation yielded an immunoreactive protein with an apparent molecular mass of 75 kDa, which is similar to the size of a chitinase present in pharate pupal molting fluid. Southern blot analysis indicated that one or two genes related to the cDNA clone are encoding chitinases in the Manduca genome. The major tissues expressing chitinase genes were the epidermis and gut with mRNA levels highest on c. days 5-7 during the fifth larval instar. Injection of 20-hydroxyecdysone into ligated fifth instar abdomens caused about a 10-fold increase in mRNA levels in both epidermis and gut, and topical application of the juvenile hormone mimic, fenoxycarb, suppressed the ecdysteroid-induced accumulation of chitinase RNA.