Dissociation and Reassociation of Xanthomonas α-Amino Acid Ester Hydrolase

We isolated a cDNA for basic class I chitinase (ChitiWb1). ChitiWb1 cDNA encodes a protein that consists of 315 amino acid residues and has a signal peptide. Northern blot analysis indicated that the class I chitinase mRNA in leaves and cultured cells of winged bean was increased by treatments with NaCl, KCl, CaCl₂, mannitol or saccharose, but not with abscisic acid. Thus, class I chitinase expression was shown to be up-regulated by osmotic stress.     

Removal of Vacuolar Targeting Signal from Class I Vacuolar Chitinase leads to its Extracellular Secretion in Transgenic Tobacco

Chitinase, an antifungal pathogenesis related (PR) protein is present in different isoforms. Class I basic chitinase which is generally more antifungal in nature compared to other chitinase classes, is present in vacuoles. It is speculated that extracellular secretion of this vacuolar enzyme by removing its vacuolar targeting signal at C- terminus might further increase its effectivity. Tobacco class I chitinase cDNA was earlier modified by PCR to add two stop codons before vacuolar targeting signal, so that the protein without this signal would be secreted extracellularly.Transgenic tobacco plants were raised with modified chitinase cDNA and native unmodified cDNA, both under the control of CaMV 35 S promoter, using Agrobacterium mediated transformation. Transgenic plants with unmodified class I chitinase cDNA expressed the enzyme in vacuoles and those having modified cDNA expressed the enzyme in extracellular spaces while retaining its biological activity.     

Cloning and characterization of a small family 19 chitinase from moss (Bryum coronatum)

Chitinase-A (BcChi-A) was purified from a moss, Bryum coronatum, by several steps of column chromatography. The purified BcChi-A was found to be a molecular mass of 25 kDa by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and an isoelectric point of 3.5. A cDNA encoding BcChi-A was cloned by rapid amplification of cDNA ends and polymerase chain reaction. It consisted of 1012 nucleotides and encoded an open reading frame of 228 amino acid residues. The predicted mature BcChi-A consists of 205 amino acid residues and has a molecular weight of 22,654. Sequence analysis indicated that BcChi-A is glycoside hydrolase family-19 (GH19) chitinase lacking loops I, II, IV and V, and a C-terminal loop, which are present in the catalytic domain of plant class I and II chitinases. BcChi-A is a compact chitinase that has the fewest loop regions of the GH19 chitinases. Enzymatic experiments using chitooligosaccharides showed that BcChi-A has higher activity toward shorter substrates than class II enzymes. This characteristic is likely due to the loss of the loop regions that are located at the end of the substrate-binding cleft and would be involved in substrate binding of class II enzymes. This is the first report of a chitinase from mosses, nonvascular plants.     

Molecular characterization of four chitinase cDNAs obtained fromCladosporium fulvum-infected tomato

Complementary DNA clones encoding acidic and basic isoforms of tomato chitinases were isolated fromCladosporium fulvum-infected leaves. The clones were sequenced and found to encode the 30 kDa basic intracellular and the 26 and 27 kDa acidic extracellular tomato chitinases previously purified (M.H.A.J. Joostenet al., in preparation). A fourth truncated cDNA which appears to encode an extracellular chitinase with 82% amino acid similarity to the 30 kDa intracellular chitinase was also isolated. Characterization of the clones revealed that the 30 kDa basic intracellular protein is a class I chitinase and that the 26 and 27 kDa acidic extracellular proteins which have 85% peptide sequence similarity are class II chitinases. The characterized cDNA clones represent four from a family of at least six tomato chitinases. Southern blot analysis indicated that, with the exception of the 30 kDa basic intracellular chitinase, the tomato chitinases are encoded by one or two genes. Northern blot analysis showed that the mRNA encoding the 26 kDa acidic extracellular chitinase is induced more rapidly during an incompatibleC. fulvum-tomato interaction than during a compatible interaction. This difference in timing of mRNA induction was not observed for the 30 kDa basic intracellular chitinase.     

A tobacco gene encoding a novel basic class II chitinase: a putative ancestor of basic class I and acidic class II chitinase genes

Various chitinases have been identified in plants and categorized into several groups based on the analysis of their sequences and domains. We have isolated a tobacco gene that encodes a predicted polypeptide consisting of a 20-amino acid N-terminal signal peptide, followed by a 245-amino acid chitinolytic domain. Although the predicted mature protein is basic and shows greater sequence identity to basic class I chitinases (75%) than to acidic class II chitinases (67%), it lacks the N-terminal cysteine-rich domain and the C-terminal vacuolar targeting signal that is diagnostic for class I chitinases. Therefore, this gene appears to encode a novel, basic, class II chitinase, which we have designated NtChia2;B1. Accumulation of Chia2;B1 mRNA was induced in leaves in association with the local-lesion response to tobacco mosaic virus (TMV) infection, and in response to treatment with salicylic acid, but was only slightly induced by treatment with ethephon. Little or no Chia2;B1 mRNA was detected in roots, flowers, and cell-suspension cultures, in which class I chitinase mRNAs accumulate to high concentrations. Sequence comparisons of Chia2;B1 with known tobacco class I and class II chitinase genes suggest that Chia2;B1 might encode an ancestral prototype of the present-day class I and class II isoforms. Possible mechanisms for chitinase gene evolution are discussed.     

Characterzation of chitinases able to rescue somatic embryos of the temperature-sensitive carrot variantts11

To characterize the acidic endochitinase EP3, able to rescue somatic embryos of the carrot cell linets11, the enzyme was purified from the medium of wild-type suspension cultures. Peptide sequences, deduced amino acid sequences of corresponding PCR-generated cDNA clones, serological relation and biochemical properties showed that there were at least five closely related chitinases, four of which could be identified as class IV EP3 chitinases with an apparent size of 30 kDa. Two other proteins were identified as a serologically related class I acidic chitinase (DcChitI) of 34 kDa, and a serologically unrelated 29 kDa class II acidic chitinase (DcChitII), respectively. Additional cDNA sequences, Western and Southern analysis showed the presence of a least two, but possibly more, highly homologous class IV EP3 genes in the carrot genome. Two class IV EP3 chitinases were tested and found to be able to increase the number ofts11 globular embryos formed under non-permissive conditions. One of the class IV EP3 chitinases as well as the class I chitinase DcChitI promoted the transition from globular to heart-stagets11 embryos. The class II endochitinase and a heterologous class IV chitinase from sugar-beet were not active onts11. This suggests that there are differences in the specificity of chitinases in terms of their effect on plant somatic embryos.     

Cloning,expression, and characterization of an antifungal chitinase from Leucaena leucocephala de Wit

Chitinase cDNAs from Leucaena leucocephala seedlings were cloned by PCR amplification with degenerate primers based on conserved class I chitinase sequences and cDNA library screening. Two closely related chitinase cDNAs were sequenced and inferred to encode precursor proteins of 323 (KB1) and 326 (KB2) amino acids. Expression of the KB2 chitinase from a pET32a plasmid in Origami (DE3) Escherichia coli produced high chitinase activity in the cell lysate. The recombinant thioredoxin fusion protein was purified and cleaved to yield a 32-kDa chitinase. The recombinant chitinase hydrolyzed colloidal chitin with endochitinase-type activity. It also inhibited growth of 13 of the 14 fungal strains tested.     

A tobacco gene encoding a novel basic class II chitinase: a putative ancestor of basic class I and acidic class II chitinase genes

Various chitinases have been identified in plants and categorized into several groups based on the analysis of their sequences and domains. We have isolated a tobacco gene that encodes a predicted polypeptide consisting of a 20-amino acid N-terminal signal peptide, followed by a 245-amino acid chitinolytic domain. Although the predicted mature protein is basic and shows greater sequence identity to basic class I chitinases (75%) than to acidic class II chitinases (67%), it lacks the N-terminal cysteine-rich domain and the C-terminal vacuolar targeting signal that is diagnostic for class I chitinases. Therefore, this gene appears to encode a novel, basic, class II chitinase, which we have designated NtChia2;B1. Accumulation of Chia2;B1 mRNA was induced in leaves in association with the local-lesion response to tobacco mosaic virus (TMV) infection, and in response to treatment with salicylic acid, but was only slightly induced by treatment with ethephon. Little or no Chia2;B1 mRNA was detected in roots, flowers, and cell-suspension cultures, in which class I chitinase mRNAs accumulate to high concentrations. Sequence comparisons of Chia2;B1 with known tobacco class I and class II chitinase genes suggest that Chia2;B1 might encode an ancestral prototype of the present-day class I and class II isoforms. Possible mechanisms for chitinase gene evolution are discussed. Received: 25 May 1998 / Accepted: 29 June 1998     

Cloning, sequencing, and expression of the tulip bulb chitinase-1 cDNA

A cDNA encoding tulip bulb chitinase-1 (TBC-1) was cloned using a combination of immunoscreening from a lambda ZAP cDNA library with anti-TBC-1 antiserum and the 5' rapid amplification of cDNA end (RACE) method, and sequenced. The cDNA consists of 1,106 nucleotides and included an open reading frame encoding a polypeptide of 314 amino acids. Comparison of the deduced amino acid sequence and the determined protein sequence indicated the presence of a signal peptide and an extra peptide composed of 26 and 13 amino acids at the N- and C-termini, respectively. The deduced sequence of TBC-1 had 10-20% and 63% sequence similarities to plant class III chitinases and gladiolus bulb class IIIb chitinase (GBC-a), respectively. The cDNA encoding mature TBC-1 was amplified by polymerase chain reaction (PCR), ligated into the expression vector pET-22b, and expressed in Escherichia coli BL21(DE3). The recombinant TBC-1 (rTBC-1) expressed in E. coli was purified by gel filtration followed by ion-exchange chromatography. Specific activity of the rTBC-1 was almost same as the authentic TBC-1 toward glycolchitin. This is the first report on the cDNA cloning of a class III chitinase having C-terminal extra peptide.     

Identification and molecular characterization of a chitinase from the hard tick Haemaphysalis longicornis

A cDNA encoding tick chitinase was cloned from a cDNA library of mRNA from Haemaphysalis longicornis eggs and designated as CHT1 cDNA. The CHT1 cDNA contains an open reading frame of 2790 bp that codes for 930 amino acid residues with a coding capacity of 104 kDa. The deduced amino acid sequence shows a 31% amino acid homology to Aedes aegypti chitinase and a multidomain structure containing one chitin binding peritrophin A domain and two glycosyl hydrolase family 18 chitin binding domains. The endogenous chitinase of H. longicornis was identified by a two-dimensional immunoblot analysis with mouse anti-rCHT1 serum and shown to have a molecular mass of 108 kDa with a pI of 5.0. A recombinant baculovirus AcMNPV.CHT1-expressed rCHT1 is glycosylated and able to degrade chitin. Chitin degradation was ablated by allosamidin in a dose-dependent manner. The optimal temperature and pH for activity of the purified chitinase were 45 degrees C and pH 5-7. The CHT1 cDNA has an ELR motif for chemokine-mediated angiogenesis and appears to be a chitinase of the chemokine family. Localization analysis using mouse anti-rCHT1 serum revealed that native chitinase is highly expressed in the epidermis and midgut of the tick. AcMNPV.CHT1 topically applied to H. longicornis ticks exhibited replication. This is the first report of insect baculovirus infection of ticks. The importance of AcMNPV.CHT1 as a novel bio-acaricide for tick control is discussed.     

Use of alternate splice sites in granule-bound starch synthase mRNA from low-amylose rice varieties

A soybean chitinase which has an apparent molecular mass of 28 kDa by SDS-PAGE, and has chitinase specific activity of 133 units per mg protein at pH 5.2 and an apparent pI of 5.7, was purified from mature dry seeds. Based upon the selected part (the residue positions 10–17) of the determined N-terminal 38 amino acid sequence, a 23-mer degenerate oligonucleotide was synthesized and used for the PCR cloning of the chitinase cDNA. The resulting 1340 bp cDNA was comprised of a 5-untranslated region of 39 bases, a coding region corresponding to a 25 amino acid signal sequence, followed by a mature 308 amino acid sequence (calculated molecular mass 34269, calculated pI 4.7), and a 235 nucleotide 3-terminal untranslated region including 24 bases of the poly(A) tail. By comparing the deduced primary sequence with those of plant chitinases known to date, this enzyme was more than 50% identical to every class III acidic chitinase, but has no significant similarity to other families of chitinases. The comparison also showed that the C-termininal region of this chitinase is markedly extended, by at least 31 residues. Northern blot analysis demonstrated that this mRNA species is remarkably transcribed from the early stage until the late middle stage of seed development, whilst it is hardly expressed in the leaves and the stems of soybean. Spatial and temporal expression of this single gene imply that this class III chitinase is mainly devoted to the seed defense, not only in development but also in dormancy of soybean seed. This is the first reported isolation and cDNA cloning of a class III acidic endochitinase from seeds. According to the chitinase nomenclature we propose that this enzyme would be classified into a new class of chitinase PR-8 family, together with a Sesbania homologue.     

Purification,cDNA cloning,and characterization of LysM-containing plant chitinase from horsetail (Equisetum arvense)

Chitinase-A (EaChiA), molecular mass 36 kDa, was purified from the vegetative stems of a horsetail (Equisetum arvense) using a series of column chromatography. The N-terminal amino acid sequence of EaChiA was similar to the lysin motif (LysM). A cDNA encoding EaChiA was cloned by rapid amplification of cDNA ends and polymerase chain reaction. It consisted of 1320 nucleotides and encoded an open reading frame of 361 amino acid residues. The deduced amino acid sequence indicated that EaChiA is composed of a N-terminal LysM domain and a C-terminal plant class IIIb chitinase catalytic domain, belonging to the glycoside hydrolase family 18, linked by proline-rich regions. EaChiA has strong chitin-binding activity, however, no antifungal activity. This is the first report of a chitinase from Equisetopsida, a class of fern plants, and the second report of a LysM-containing chitinase from a plant.     

A new class of tobacco chitinases homologous to bacterial exo-chitinases displays antifungal activity

A novel chitinase gene of tobacco was isolated and characterized by DNA sequence analysis of a genomic clone and a cDNA clone. Comparative sequence analysis of both clones showed an identity of 94%. The proteins encoded by these sequences do not correspond to any of the previously characterized plant chitinases of classes I–IV and are designated as class V chitinases. Comparison of the chitinase class V peptide sequence with sequences in the Swiss Protein databank revealed significant sequence similarity with bacterial exo-chitinases from Bacillus circulans, Serratia marcescens and Streptomyces plicatus. It was demonstrated that class V chitinase gene expression is induced after treatment of tobacco with different forms of stress, like TMV-infection, ethylene treatment, wounding or ultraviolet irradiation. Two related chitinase class V proteins of 41 and 43 kDa were purified from Samsun NN tobacco leaves inoculated with tobacco mosaic virus. The proteins were purified by Chelating Superose chromatography and gel filtration. In vitro assays demonstrated that class V chitinases have endo-chitinase activity and exhibit antifungal activity toward Trichoderma viride and Alternaria radicina. In addition, it was shown that class V chitinase acts synergistically with tobacco class I β-1,3-glucanase against Fusarium solani germlings.     

The complete amino acid sequence of yam (Dioscorea japonica) chitinase. A newly identified acidic class I chitinase.

The complete amino acid sequence of acidic chitinase from yam (Dioscorea japonica) aerial tubers was determined. The protein is composed of a single polypeptide chain of 250 amino acid residues and has a calculated molecular mass of 27,890 Da. There is an NH2-terminal domain, a hinge region, and a main structure, typical for class I chitinases (Shinshi, H., Neuhaus, J.-M., Ryals, J., and Meins, F., Jr. (1990) Plant Mol. Biol. 14, 357-368). We have obtained the first evidence for an acidic class I chitinase. Comparison with sequences of other class I chitinases revealed approximately 40% sequence similarity, a value lower than that for other class I chitinases (70-80%). We assume that there is a local conformational change in the molecule; cysteine residues that probably form disulfide bonds are completely conserved, with the exception of Cys-178. The difference in structure between this chitinase and other basic class I chitinases suggests that acidic and basic isoforms should be grouped into subclasses; this protein is an ethylene- or a pathogen-independent chitinase produced by a gene that is inherent in the tuber.     

Cloning and expression of a fat body-specific chitinase cDNA from the spider, Araneus ventricosus

A fat body-specific chitinase cDNA was cloned from the spider, Araneus ventricosus. The cDNA encoding A. ventricosus chitinase (AvChit1) is 1515 bp long with an open reading frame (ORF) of 431 amino acid residues. AvChit1 possesses the chitinase family 18 active site signature and one N-glycosylation site. The deduced amino acid sequence of AvChit1 cDNA showed 43% identity to both Glossina morsitans morsitans chitinase and a human chitotriosidase, and 30-40% to some insect chitinases which lack both the serine/threonine and chitin binding domains. Southern blot analysis of genomic DNA suggested the presence of AvChit1 gene as a single copy. Northern and Western blot analysis and enzyme activity assay showed the tissue-specific expression of AvChit1 in the A. ventricosus fat body. The AvChit1 cDNA was expressed as a 61 kDa polypeptide in baculovirus-infected insect Sf9 cells and the recombinant AvChit1 showed activity in the chitinase enzyme assay using 0.1% glycol chitin as a substrate. Treatment of recombinant virus-infected Sf9 cells with tunicamycin, a specific inhibitor of N-glycosylation, revealed that AvChit1 is N-glycosylated, but the carbohydrate moieties are not essential for chitinolytic activity.