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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.
Mol Gen Genet 1998 Sep
PMID:A tobacco gene encoding a novel basic class II chitinase: a putative ancestor of basic class I and acidic class II chitinase genes. 979 May 82

Alfalfa (Medicago sativa) varieties with antibiosis-based resistance to the root-lesion nematode (Pratylenchus penetrans), a migratory endoparasite of many crops, have been developed by recurrent selection. Individual plants from these varieties that support significantly lower nematode reproduction were identified for molecular and biochemical characterization of defense responses. Before nematode infection, RNA blot analysis revealed 1.3-1.8-fold higher phenylpropanoid pathway mRNA levels in roots of three resistant plants as compared to three susceptible alfalfa plants. The mRNAs encoded the first enzyme in the pathway (phenylalanine ammonia-lyase), the first in the pathway branch for flavonoid biosynthesis (chalcone synthase), a key enzyme in medicarpin biosynthesis (isoflavone reductase) and a key enzyme in the pathway branch for biosynthesis of lignin cell wall precursors (caffeic acid O-methyltransferase). After nematode infection, the mRNAs declined over 48 h in resistant roots but rose in susceptible plants during the first 12 h after-infection and then declined. Acidic beta-1,3-glucanase mRNA levels were initially similar in both root types but accumulated more rapidly in resistant than in susceptible roots after nematode infection. Levels of a class I chitinase mRNA were similar in both root types. Histone H3.2 mRNA levels, initially 1.3-fold higher in resistant roots, declined over 6-12 h to levels found in susceptible roots and remained stable in both root types thereafter. Defense-response gene transcripts in roots of nematode-resistant and susceptible alfalfa plants thus differed both constitutively and in inductive responses to nematode infection. HPLC analysis of isoflavonoid-derived metabolites of the phenylpropanoid pathway revealed similar total constitutive levels, but varying relative proportions and types, in roots of the resistant and susceptible plants. Nematode infection had no effect on isoflavonoid levels. Constitutive levels of the phytoalexin medicarpin were highest in roots of the two most resistant plants. Medicarpin inhibited motility of P. penetrans in vitro.
Plant Mol Biol 1998 Dec
PMID:Alfalfa (Medicago sativa L.) resistance to the root-lesion nematode, Pratylenchus penetrans: defense-response gene mRNA and isoflavonoid phytoalexin levels in roots. 986 6

The molecular packing in beta-chitin unit cells was experimentally determined by a combination of unidirectional degradation by Bacillus circulans chitinase A1 and microdiffraction electron crystallography using highly crystalline beta-chitin microfibrils from the protective tubes secreted by Lamellibrachia satsuma. The mode of chain packing was found to be identical with that of the previously published crystal model for beta-chitin, despite a controversial definition of the unit cell parameters. Here, a "parallel-down" packing was determined, where the reducing ends of chains point in an opposite direction to the crystallographic c-axis. Microdiffraction analyses of nascent beta-chitin microfibrils generated from diatom Thalassiosira sp. showed that the c-axis of the crystal was directed toward the diatoms, and therefore the reducing end of a growing chain pointed away from the locus of biosynthesis. This mechanism agreed well with what we found recently in the cellulose biosynthesis system, and provides strong evidence that the polymerization by the processive glycosyl transferase takes place at the non-reducing end of the growing polysaccharide chains.
J Mol Biol 1999 Feb 12
PMID:Molecular directionality of beta-chitin biosynthesis. 993 Dec 63

Urtica dioica agglutinin (UDA) has previously been found in roots and rhizomes of stinging nettles as a mixture of UDA-isolectins. Protein and cDNA sequencing have shown that mature UDA is composed of two hevein domains and is processed from a precursor protein. The precursor contains a signal peptide, two in-tandem hevein domains, a hinge region and a carboxyl-terminal chitinase domain. Genomic fragments encoding precursors for UDA-isolectins have been amplified by five independent polymerase chain reactions on genomic DNA from stinging nettle ecotype Weerselo. One amplified gene was completely sequenced. As compared to the published cDNA sequence, the genomic sequence contains, besides two basepair substitutions, two introns located at the same positions as in other plant chitinases. By partial sequence analysis of 40 amplified genes, 16 different genes were identified which encode seven putative UDA-isolectins. The deduced amino acid sequences share 78.9-98.9% identity. In extracts of roots and rhizomes of stinging nettle ecotype Weerselo six out of these seven isolectins were detected by mass spectrometry. One of them is an acidic form, which has not been identified before. Our results demonstrate that UDA is encoded by a large gene family.
Plant Mol Biol 1999 Jan
PMID:Characterization of Urtica dioica agglutinin isolectins and the encoding gene family. 1008 Jun 99

Expression patterns of chitinase transcripts induced by N-acetylchitooligosaccharide elicitor were analyzed by northern blot hybridization in order to reveal a signal transduction pathway leading to the activation of class I chitinase genes (Cht-1 and Cht-3), which may play an important role in producing N-acetylchitooligosaccharide elicitor. The transcription level of both genes was enhanced in response to N-acetylchitooligosaccharides larger than pentaose at subnanomolar concentrations. These structure and dose dependencies were consistent not only with those for a 75 kDa high-affinity binding protein for N-acetylchitooligosaccharide elicitor in the plasma membrane, but also with other series of cellular responses including phytoalexin production and the expression of elicitor-responsive genes (EL2, EL3). Therefore, the elicitor signal to evoke these cellular responses including the activation of the chitinase genes could be common and transmitted into cells through the 75 kDa protein. However, the signal transduction pathway for the activation of the chitinase gene appeared to diverge from those for the other elicitor-responsive genes shortly after the signal perception. It was shown that the induction of chitinase expression by N-acetylchitooligosaccharide would require protein phosphorylation, but not de novo protein synthesis. The oxidative burst was demonstrated not to be necessary for transcriptional induction of the all four elicitor-responsive genes (Cht, PAL, EL2, EL3) by N-acetylchitooligosaccharide.
Plant Mol Biol 1999 Mar
PMID:Regulation of the chitinase gene expression in suspension-cultured rice cells by N-acetylchitooligosaccharides: differences in the signal transduction pathways leading to the activation of elicitor-responsive genes. 1034 96

The nuclear matrix is thought to partition the genome into functional and structural loop domains, and it has been implicated in several cellular processes, such as the replication and transcription of DNA and the processing of RNA. Therefore, the analysis of scaffold/matrix-associated DNA regions (S/MARs) might enhance our understanding of the functional roles of the higher-order organization of chromatin. In this study, the upstream region between positions -3320 and -1095 of the basic class I chitinase gene, CHN50, was shown to have specific affinity for the tobacco nuclear scaffold. Detailed analysis of nuclear scaffold-DNA binding in vitro revealed that two regions (positions -3320 to -2621 and -2221 to -1371) bound specifically to the nuclear scaffold. These S/MAR elements, designated S/M I and S/M II, are A+T-rich sequences with 75% and 74% A+T residues, respectively, and may include a number of sequence motifs that have frequently been found in other S/MARs. Moreover, S/M II contains a curved DNA sequence with anomalous mobility on polyacrylamide gels. A circular permutation assay revealed that the center of this curved region was located between positions -1767 and -1759. The possible functions and structural features of the S/MAR elements in the upstream region of CHN50 are discussed.
Plant Mol Biol 1999 Mar
PMID:Characterization of matrix attachment sites in the upstream region of a tobacco chitinase gene. 1034 9

We have isolated cDNA clones encoding class I chitinase (ChtC) from potato leaves which share a high degree of nucleotide and amino acid sequence similarity to other, previously described basic (class I) chitinases (ChtB) from potato. Despite this similarity, characteristic features distinguish ChtC from ChtB, including an extended proline-rich linker region between the hevein and catalytic domains and presence of a potential glycosylation site (NDT) in the deduced protein. These differences are in accordance with the properties of purified chitinase C which is glycosylated and hence has a higher molecular mass in comparison to chitinase B. In contrast to the coding sequences, the 3'-untranslated regions of ChtC and ChtB exhibited a low degree of similarity, which allowed us to generate gene-specific probes to study the genomic organization and expression of both types of gene. Genomic DNA blots suggest that ChtC and ChtB are each encoded by one or two genes per haploid genome. RNA blot analysis showed that in healthy potato plants ChtC mRNA is most abundant in young leaves, the organs which also contain high levels of chitinase C. By contrast, ChtB mRNA abundance is highest in old leaves, which accumulate chitinase B. By in situ RNA hybridization with gene-specific probes we could demonstrate that ChtC mRNA in leaves is restricted to epidermal cells, whereas ChtB mRNA showed no distinct pattern of cell-type-specific localization. Infection of potato leaves with Phytophthora infestans, or treatment with fungal elicitor, ethylene, or wounding resulted in accumulation of both ChtC and ChtB mRNAs; however, for ChtC, in contrast to ChtB, no corresponding accumulation of the encoded protein could be detected, suggesting a post-transcriptional mechanism of regulation. Salicylic acid treatment did not induce accumulation of either mRNA. The possible functional implications of these findings for pathogen defence and developmental processes are discussed.
Plant Mol Biol 1999 Apr
PMID:A distinct member of the basic (class I) chitinase gene family in potato is specifically expressed in epidermal cells. 1038 Aug 1

A cDNA encoding a chitinase of Pheadon cochleariae was isolated from a larval gut library. The cDNA encodes a preenzyme with a putative 20 amino-acid signal peptide and a 385 amino-acid mature enzyme of calculated mass of 42.7 kDa. Amino-acid alignment shows 24-33% identity to other insect and crustacea chitinases. The sequence lacks C-terminus domains but active site residues are conserved. Northern analysis localizes the mRNA to guts of feeding larvae. Southern blot analysis, with a complete cDNA probe, suggests that the P. cochleariae genome may contain several chitinase genes. Activity gels show that two groups of chitinases are expressed in the insect. One group comprises chitinases of 30-40 kDa that are active at pH 5.0 and detected in guts of feeding larvae and adults, as well as in pre-pupae and pupae. The other group comprises chitinases of 40-70 kDa that are more active at pH 7.0 and are mainly expressed in pre-pupae and pupae. The biological significance of both groups of chitinases is discussed.
Insect Biochem Mol Biol 1999 Jun
PMID:Molecular cloning of a gut-specific chitinase cDNA from the beetle Phaedon cochleariae. 1040 92

A gene encoding chitinase from Serratia marcescens BJL200 was cloned into a broad-host-range vector (pRK415) and mobilized into Sinorhizobium fredii USDA191. Chitinolytic activity was detected in S. fredii USDA191 transconjugants that carried the S. marcescens chiB gene. Chitinase-producing S. fredii USDA191 formed nodules on soybean cultivar McCall. However, there was a delay in nodule formation and a marked decrease in the total number of nodules formed by the chitinase-producing S. fredii in comparison with the wild-type strain. Expression of chitinase in S. meliloti RCR2011 also impeded alfalfa nodulation. Thin-layer chromatography of 14C-labeled Nod factors from chitinase-producing S. fredii USDA191 revealed hydrolysis of lipochitooligosaccharides.
Mol Plant Microbe Interact 1999 Aug
PMID:Expression of a Serratia marcescens chitinase gene in Sinorhizobium fredii USDA191 and Sinorhizobium meliloti RCR2011 impedes soybean and alfalfa nodulation. 1043 38

The yeast transcription factor Ace2p regulates expression of the chitinase gene CTS1 in a cell cycle-dependent manner. Nuclear localisation of Ace2p is restricted to late M and early G phases of the mitotic cell cycle. We show here that this nuclear localisation is directly associated with regulation of CTS1 expression. Using a version of Ace2p tagged with a c-myc epitope, we show that the protein is excluded from the nucleus of cells during most phases of the mitotic cell cycle. A mutant derivative in which one threonine and two serine residues, which are candidate phosphorylation sites, were replaced by alanine (to mimic constitutive dephosphorylation) is localised in the nucleus throughout the cell cycle. The mechanism of localisation of Ace2p therefore involves regulation of its phosphorylation state, and closely resembles that used by the homologous transcription factor Swi5p. The wild-type Ace2 protein associates with Cdc28p in vivo, suggesting this may be the kinase that mediates the phosphorylation event. The stability of the protein is greatly reduced in a mutant that is constitutively localised to the nucleus, but is restored in a deletion derivative which remains in the cytoplasm. Ace2p is therefore controlled throughout the cell cycle at three levels: transcription, nuclear localisation, and proteolysis.
Mol Gen Genet 1999 Sep
PMID:Regulated nuclear localisation of the yeast transcription factor Ace2p controls expression of chitinase (CTS1) in Saccharomyces cerevisiae. 1051 23


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