Structure and expression of a barley acidic beta-glucanase gene

Powdery mildew pathogens can suppress the chitinase gene expression induced in detached inner epidermis of barley coleoptile

Two-step PCR (RT-PCR and nested PCR) was used to detect gene expression in powdery mildew pathogen-infected cells of detached inner epidermis of barley coleoptiles. Cellular contents of infected cells were microscopically suctioned with a micropipette and subjected to PCR. Triosephosphate isomerase and glyceraldehyde-3-phosphate dehydrogenase genes involved in the glycolytic pathway and a stimulus-induced endochitinase gene were targeted, and their expression was determined by detecting cDNAs derived from spliced transcripts. The two gycolysis-related genes were constantly expressed in the tissue irrespective of pathogen inoculation. In contrast, chitinase gene expression was induced in non-infected inner epidermis after detachment. After inoculation, this expression was selectively suppressed in pathogen-invaded cells, in spite of continuous expression in non-invaded cells of the same epidermis. Thus, the present method enabled us to directly analyze transcripts in individual cells at the infection site and assess the capability of the pathogen to regulate host gene expression.

Effect of manganese toxicity on the proteome of the leaf apoplast in cowpea

Excess manganese (Mn) supply causes formation of visible brown depositions in the cell walls of leaves of cowpea (Vigna unguiculata), which consist of oxidized Mn and oxidized phenols. Because oxidation of Mn and phenolic compounds in the leaf apoplast was proposed to be catalyzed by apoplastic peroxidases (PODs), induction of these enzymes by Mn excess was investigated. POD activity increased upon prolonged Mn treatment in the leaf tissue. Simultaneously, a significant increase in the concentration of soluble apoplastic proteins in "apoplastic washing fluid" was observed. The identity of the released proteins was systematically characterized by analysis of the apoplast proteome using two-dimensional gel electrophoresis and liquid chromatography-tandem mass spectrometry. Some of the identified proteins exhibit sequence identity to acidic PODs from other plants. Several other proteins show homologies to pathogenesis-related proteins, e.g. glucanase, chitinase, and thaumatin-like proteins. Because pathogenesis-related-like proteins are known to be induced by various other abiotic and biotic stresses, a specific physiological role of these proteins in response to excess Mn supply remains to be established. The specific role of apoplastic PODs in the response of plants to Mn stress is discussed.

Isolation of fungal cell wall degrading proteins from barley (Hordeum vulgare L.) leaves infected with Rhynchosporium secalis

Proteins with antifungal activity towards Rhynchosporium secalis conidia were isolated from the intercellular washing fluid (IWF) of barley leaves. The active components were purified by high-performance liquid chromatography under conditions that maintained biological activity. Five major barley IWF proteins deleterious to the cell wall of viable R. secalis conidia were isolated and identified by a combination of N-terminal amino acid sequencing, peptide mapping, and determination of mass and isoelectric point. They were a 32-kDa beta-1,3-glucanase (Pr32), a 25-kDa chitinase (Pr25), and three 22-kDa thaumatin-like (TL) proteins (Pr22-1, Pr22-2, and Pr22-3). Pr22-1 and Pr22-2 were similar to the protein R class of TL proteins, whereas Pr22-3 was more similar to the S class. Pr22-3 was shown to digest laminarin, indicating that this TL protein has glucanase activity. In addition, Pr22-3 was more active in the spore bioassay than Pr22-2. Various combinations of the five proteins had a greater effect on R. secalis spores than did the individual proteins. The extraction of proteins with antifungal activity from the IWF of barley leaves indicates their possible role in defense against leaf pathogens. A similar bioassay may be developed for other systems to identify particular isoforms of pathogenicity-related proteins that might have a role in plant disease resistance.

Pathogenesis-related proteins of plants as allergens

OBJECTIVE

Many pathogenesis-related (PR) proteins from plants are allergenic. We review the evidence that PR proteins represent an increasingly important group of plant-derived allergens.

DATA SOURCES

A detailed literature search was conducted through PubMed and GenBank databases.

STUDY SELECTION

All reports in PubMed and GenBank related to PR protein allergens for which at least partial amino acid sequence is known were included.

RESULTS

Production of PR proteins by plants is induced in plants by stress. Members of PR-protein groups 2, 3, 4, 5, 8, 10, and 14 have demonstrated allergenicity. PR2-, 3-, 4-, and 8-homologous allergens are represented by the latex allergens. Cross-reactivity of PR3 latex allergen, Hev b 6.02, with some fruit allergens may be a reflection of the representation of homologous PR proteins among varied plants. The expression of one of the representative PR5-homologous cedar pollen allergens, Jun a 3, is highly variable across years and geographic areas, possibly because of variable induction of this PR protein by environmental factors. PR10-homologous birch pollen allergen, Bet v 1, is structurally similar to and cross-reacts with PR10 proteins from fruits (eg, Mal d 1) which cause oral allergy syndrome. PR14 allergens (eg, Zea m 14) consist of lipid transfer proteins found in grains and fruits and are inducers of anaphylaxis.

CONCLUSIONS

PR-homologous allergens are pervasive in nature. Similarity in the amino acid sequences among members of PR proteins may be responsible for cross-reactivity among allergens from diverse plants. Induced expression of PR-homologous allergens by environmental factors may explain varying degrees of allergenicity. Man-made environmental pollutants may also alter the expression of some PR protein allergens.

New perspectives on the endo-beta-glucanases of glycosyl hydrolase Family 17

Isozymes of glycosyl hydrolase Family 17 hydrolyze 1,3-beta-glucan polysaccharides found in the cell wall matrix of plants and fungi, enabling these plant enzymes to serve diverse roles in plant defense and plant development. Fourteen genes from Family 17 have been characterized in the genome of rice. A sequence dendrogram analysis divided these genes into four subfamilies. The recombinant GNS1 enzyme from subfamily B had 1,3;1,4-beta-glucanase activity, suggesting a role for this isozyme in plant development.

Molecular size and net charge of pathogenesis-related enzymes from barley (Hordeum vulgare L., v. Karat) infected with Drechslera teres f. teres (Sacch.) Shoem

Molecular size and net charge of isoforms of pathogenesis-related (PR) chitinase, beta-1,3-glucanase and peroxidase were studied in uninfected barley (Hordeum vulgare L., v. Karat) leaves and in barley leaves infected with the pathogenic fungus Drechslera teres f. teres (Sacch.) Shoem. Molecular characteristics were determined by time-dependent polyacrylamide gradient gel electrophoresis under native conditions and by applying an extended version of the computer program MOL-MASS (Rothe, G. M., Weidmann, H., Electrophoresis 1991, 12, 703-709). Uninfected barley leaves contained predominantly one peroxidase isozyme but also three very weak peroxidases. Activities of all of these three peroxidases increased considerably after infection with Drechslera teres. The molecular masses of peroxidases 1 and 3 were estimated to be 38 +/- 5 and 42 +/- 7 kDa and their apparent valences at pH 8.4 were Z = 3.13 and 3.20, respectively. Amongst the chitinase isoforms, chitinase 1 and chitinase 2 appeared after infection, while chitinase 3 was also observed in uninfected leaves of barley. The molecular mass of chitinase 3 (31 +/- 6 kDa; f/fo = 1.20) was larger than that of chitinase 1 (20 +/- 2 kDa; f/fo = 1.04) and chitinase 2 (23 +/- 3 kDa; f/fo = 1.06). The valence of constitutive chitinase 3 (Z = 1.44 +/- 0.81) at pH 8.4 was lower than that of adaptive chitinase 1 (Z = 3.27 +/- 1.02) and chitinase 2 (Z = 2.96 +/- 1.38). Infection of barley leaves with Drechslera teres also induced the hydrolytic enzyme beta-1,3-glucanase 1; beta-1,3-glucanase 2 appeared in uninfected and in infected leaves. Constitutive beta-1,3-glucanase 2 was smaller (molecular mass 19 +/- kDa; f/fo = 1.05) than adaptive beta-1,3-glucanase 1 (molecular mass 26 +/- 4 kDa; f/fo = 1.07). The valence of adaptive beta-1,3-glucanase 1 (Z = 9.58 +/- 4.17) was approximately threefold that of beta-1,3-glucanase 2 (Z = 2.80 +/- 0.93).

Cloning and characterization of the genomic region encoding toxin IV-5 from the scorpion Tityus serrulatus Lutz and Mello

By means of PCR and using synthetic oligonucleotides designed from the reported cDNA, we amplified the gene that codes for toxin IV-5 from the Brazilian scorpion Tityus serrulatus. The analysis of the nucleotide sequence shows that the amplified genomic region is composed of 659 base pairs (bp) comprising two exons (28 and 284 bp) and an intron of 347 bp interrupting the region that encodes the signal peptide of the precursor toxin. Based on these findings a model for the structural organization of scorpion toxin genes is proposed.

The expression of an abundant transmitting tract-specific endoglucanase (Sp41) is promoter-dependent and not essential for the reproductive physiology of tobacco

In angiosperms the interactions between the secretory matrix of the stylar transmitting tract and the growing pollen tubes have central roles in determining a successful fertilization. Sp41 is a major glycosylated component of the soluble proteins of the transmitting tract matrix and exhibits (1-3)-beta-glucanase activity. It is a member of the pathogenesis-related protein superfamily, but shows developmental regulation as opposed to pathogen induction. In order to investigate the mechanisms regulating Sp41 expression, we isolated and characterized genomic clones corresponding to the sp41 alpha gene. Sp41 alpha contains an intervening sequence localized between the sequences encoding for a putative signal peptide and the mature protein. A fragment of 2.5 kb that lies 5' to the coding region of the gene was sufficient to confer transmitting tract specific expression to a beta-glucuronidase reporter gene in transgenic tobacco plants. The sp41 transcripts have unusually long 5'-untranslated sequences. The leader sequences contain small open reading frames, include secondary structures, and may be involved in post-transcriptional regulation. A possible function for Sp41 in reproductive physiology was tested by monitoring tobacco plants transformed with antisense stylar sp41 alpha RNA: Transgenic antisense plants with immunologically and enzymatically undetectable levels of (1-3)-beta-glucanase were obtained and their offspring analyzed. The progeny plants did not show any detectable phenotypic modifications as they had a normal flower morphology and were fully fertile.

A tetrad of ionizable amino acids is important for catalysis in barley beta-glucanases

Determination of the crystal structures of a 1,3-beta-D-glucanase (E.C. 3.2.1.39) and a 1,3-1,4-beta-D-glucanase (E.C. 3.2.1.73) from barley (Hordeum vulgare) (Varghese, J.N, Garrett, T. P. J., Colman, P. M., Chen, L., Høj, P. B., and Fincher, G. B. (1994) Proc. Natl. Acad. Sci. U.S.A. 91, 2785-2789) showed the spatial positions of the catalytic residues in the substrate-binding clefts of the enzymes and also identified highly conserved neighboring amino acid residues. Site-directed mutagenesis of the 1,3-beta-glucanase has now been used to investigate the importance of these residues. Substitution of glutamine for the catalytic nucleophile Glu231 (mutant E231Q) reduced the specific activity about 20,000-fold. In contrast, substitution of glutamine for the catalytic acid Glu288 (mutant E288Q) had less severe consequences, reducing kcat approximately 350-fold with little effect on Km. Substitution of two neighboring and strictly conserved active site-located residues Glu279 (mutant E279Q) and Lys282 (mutant K282M) led to 240- and 2500-fold reductions of Kcat, respectively, with small increases in Km. Thus, a tetrad of ionizable amino acids is required for efficient catalysis in barley beta-glucanases. The active site-directed inhibitor 2,3-epoxypropyl beta-laminaribioside was soaked into native crystals. Crystallographic refinement revealed all four residues (Glu231, Glu279, Lys282, and Glu288) to be in contact with the bound inhibitor, and the orientation of bound substrate in the active site of the glucanase was deduced.

Heterologous expression of cDNAs encoding barley (Hordeum vulgare) (1-->3)-beta-glucanase isoenzyme GV

Two cDNAs have been isolated from libraries generated from poly(A)+RNA of young barley roots and leaves, using a cDNA encoding barley (1-->3)-beta-glucanase isoenzyme GII as a probe. Nucleotide sequence analyses and ribonuclease protection assays show that the two cDNAs differ only in the length of their 3'-untranslated regions; the corresponding mRNAs are likely to originate from a single gene by tissue-specific processing at separate polyadenylation sites. When the coding region of the cDNA is expressed in E. coli, the resultant protein catalyses the hydrolysis of (1-->3)-beta-glucan with an action pattern characteristic of a (1-->3)-beta-glucan endohydrolase (EC 3.2.1.39). The enzyme has been designated isoenzyme GV of the barley (1-->3)-beta-glucanase family).