Transcriptional activation of plant defense genes by fungal elicitor, wounding, and infection

The chalcone synthase multigene family of Petunia hybrida (V30): differential, light-regulated expression during flower development and UV light induction

We have analysed the expression of the 8-10 members of the gene family encoding the flavonoid biosynthetic enzyme chalcone synthase (CHS) from Petunia hybrida. During normal plant development only two members of the gene family (CHS-A and CHS-J) are expressed. Their expression is restricted to floral tissues mainly. About 90% of the total CHS mRNA pool is transcribed from CHS-A, wheares CHS-J delivers about 10% in flower corolla, tube and anthers. Expression of CHS-A and CHS-J during flower development is coordinated and (red) light-dependent. In young seedlings and cell suspension cultures expression of CHS-A and CHS-J can be induced with UV light. In addition to CHS-A and CHS-J, expression of another two CHS genes (CHS-B and CHS-G) is induced in young seedlings by UV light, albeit at a low level. In contrast to CHS genes from Leguminoseae, Petunia CHS genes are not inducible by phytopathogen-derived elicitors. Expression of CHS-A and CHS-J is reduced to a similar extent in a regulatory CHS mutant, Petunia hybrida Red Star, suggesting that both genes are regulated by the same trans-acting factors. Comparison of the promoter sequences of CHS-A and CHS-J reveals some striking homologies, which might represent cis-acting regulatory sequences.

Differential early activation of defense-related genes in elicitor-treated parsley cells

A cDNA library from cultured parsley (Petroselinum crispum) cells was differentially screened using labeled run-off transcripts derived from nucleic of elicitor-treated and untreated cells. This resulted in the isolation of 18 independent cDNA families representing putative defense-related genes. All genes are rapidly and transiently activated after elicitor application, but the time courses of transcriptional activity exhibit considerable variations, indicating differences in the mechanisms of gene regulation.

Differential expression within a family of novel wound-induced genes in potato

Wounding in higher plants leads to an increased synthesis of specific messenger RNAs. A cDNA clone complementary to a wound-induced message from potato tubers was used to isolate a lambda clone from a genomic library of Solanum tuberosum var. Maris Piper. DNA sequence analysis has shown that this single genomic clone contains two novel wound-induced genes, called win1 and win2, organised in close tandem array. The coding sequences of these two genes are highly homologous and are interrupted by a single intron. However, the sequences of the introns and flanking regions have diverged widely. Win1 and win2 encode cysteine-rich proteins of 200 and 211 amino-acids, respectively, which show striking homologies to several chitin-binding proteins. Southern analysis of genomic DNA has shown that win1 and win2 are members of a small multi-gene family which is estimated to have a minimum of five members per haploid genome of Maris Piper and appears to be conserved within the Solanaceae. We have shown by Northern analysis and S1 mapping that the two genes exhibit differential organ-specific expression after the wounding of a potato plant.

Purification, characterization and induction of L-phenylalanine ammonia-lyase in Phaseolus vulgaris

The enzyme L-phenylalanine ammonia-lyase was purified from leaves of Phaseolus vulgaris by Sephacryl S-200 gel filtration and Sepharose-4-B--succinyl-aminoethyl-L-phenylalanine affinity chromatography. L-Phenylalanine ammonia-lyase was specifically eluted from the affinity matrix with its substrate L-phenylalanine at 20-25 degrees C. The purified enzyme was shown to be homogeneous by gel electrophoresis both in presence and absence of SDS. Its Mr, determined by gel filtration and non-denaturing gel electrophoresis, was 320,000 +/- 9000 and 330,000 +/- 4000 respectively. After SDS electrophoresis only one band of Mr 83,000 +/- 4000 was detected, indicating that the enzyme is an oligomer containing four subunits. The pH optimum of enzyme activity was 8.8-9.2. Ampholyte isoelectrofocusing in polyacrylamide demonstrated the presence of a single charged species at pH 4.2. The homogeneous enzyme catalyzed the deamination of L-phenylalanine to trans-cinnamate but did not catalyze the transamination of L-phenylalanine to L-phenylpyruvate. The enzyme showed Km 1.25 mM for L-phenylalanine. Antibodies to homogeneous L-phenylalanine ammonia-lyase recognised specific epitopes on L-phenylalanine aminotransferase as demonstrated by immunoaffinity purification and immunoblotting. The induction of L-phenylalanine ammonia-lyase activity during phaseollin biosynthesis in the Phaseolus vulgaris--Colletotrichum lindemuthianum interaction was regulated by an increase in enzyme concentration resulting from an increase in de novo synthesis of L-phenylalanine ammonia-lyase protein.

Purification of tobacco O-methyltransferases by affinity chromatography and estimation of the rate of synthesis of the enzymes during hypersensitive reaction to virus infection

The three tobacco (Nicotiana tabacum L.) S-adenosyl-L-methionine: o-diphenol-O-methyltransferases (OMTs; EC 2.1.1.6) were purified to homogeneity by affinity chromatography on adenosine-agarose. Amounts and catalytic actities of the enzymes were measured in tobacco leaves during the hypersensitive reaction to tobacco mosaic virus. The drastic increase in activity of each enzyme upon infection was shown to arise from the accumulation of enzymatic protein with constant specific enzymatic activity. Rates of OMT synthesis were determined from pulse-labeling experiments with L-[(14)C]leucine injected into the leaves. The specific radioactivities of the homogenous enzymes were compared in healthy and tobacco mosaic virus-infected tobacco. The results demonstrated that increase in OMT amounts is a consequence of de novo synthesis of the enzymes.

Co-ordinated regulation of chitinase and β-1,3-glucanase in bean leaves

Ethylene induced chitinase (EC 3.2.1.14) and β-1,3-glucanase (EC 3.2.1.29) to a similar extent in primary leaves of bean seedlings (Phaseolus vulgaris cv. Saxa). Both enzymes were purified from ethylene-treated leaves, and monospecific antibodies were raised aginst them. Ethylene treatments strongly increased the amount of immunore-active chitinase and β-1,3-glucanase. Ethylene enhanced synthesis of chitinase in vivo, as tested by immunoprecipitation after pulse-labelling with [(35)S]methionine. RNA was isolated from bean leaves and translated in a rabbit reticulocyte lysate system in vitro. The chitinase and the β-1,3-glucanase antiserum each precipitated a single polypeptide from the translation products. The precipitated polypeptides were 1500 and 4000 daltons larger, respectively, than native chitinase and native β-1,3-glucanase, indicating that the two enzymes were synthesized as precursors in vitro. The translatable mRNAs for both enzymes increased at least tenfold within 2 h in response to a treatment with ethylene. When ethylene was withdrawn after 8 h of incubation, the translatable mRNAs for both enzymes decreased somewhat more slowly, reaching the basal level about 25 h later. In all cases, there was a close correlation between the levels of translatable mRNA for chitinase and β-1,3-glucanase. A putative β-1,3-glucanase cDNA clone, pCH16, was isolated by hybrid-selected translation. The amount of β-1,3-glucanase mRNA, as measured by RNA blot analysis using pCH16 as a probe, increased rapidly in response to ethylene and decreased again after withdrawal of ethylene, indicating that the amount of hybridizable RNA and of translatable mRNA for β-1,3-glucanase were correlated. In conclusion, the results indicate that chitinase and β-1,3-glucanase are regulated co-ordinately at the level of mRNA.

Glutathione causes a massive and selective induction of plant defense genes

The reduced form of glutathione (GSH), when supplied to suspension cultured cells of bean (Phaseolus vulgaris L.) at concentrations in the range 0.01 to 1.0 millimolar, stimulates transcription of defense genes including those that encode cell wall hydroxyproline-rich glycoproteins and the phenylpropanoid biosynthetic enzymes phenylalanine ammonialyase (PAL) and chalcone synthase (CHS) involved in lignin (PAL) and phytoalexin (PAL, CHS) production. Transcriptional activation of these genes leads to marked accumulation of the corresponding transcripts, contributing to a massive change in the overall pattern of protein synthesis which closely resembles that previously observed in response to fungal elicitor. GSH causes a marked increase in extractable PAL activity, whereas the oxidized form of glutathione, constituent amino acids, or other reducing agents are inactive. Possible roles of GSH in signaling biological stress are discussed.

NAD(P)H-dependent 6'-deoxychalcone synthase activity in Glycyrrhiza echinata cells induced by yeast extract

The crude extract prepared from Glycyrrhiza echinata cells treated with yeast extract catalyzed the formation of liquiritigenin (5-deoxyflavanone) and isoliquiritigenin (6'-deoxychalcone) in addition to naringenin (5-hydroxyflavanone) when incubated with 4-coumaroyl-CoA and malonyl-CoA in the presence of high concentrations (0.1 mM or higher) of NADPH. Incubation without NADPH, or with low concentrations (0.01 mM or lower), gave only naringenin as a reaction product. With NADH (1 mM), the major product was naringenin accompanied by a small quantity of liquiritigenin. The initial product of the assay with 1 mM NADPH was isoliquiritigenin, indicating a reaction catalyzed by 6'-deoxychalcone synthase (DOCS). Subsequent formation of liquiritigenin was attributed to the presence of chalcone isomerase in the crude extract. The results constitute the first demonstration in vitro of DOCS activity which, in G. echinata cells and other leguminous plants, is involved in the biosynthesis of retrochalcone and 5-deoxyisoflavonoid-derived phytoalexins.

Chitinase cDNA cloning and mRNA induction by fungal elicitor, wounding, and infection

Chitinase, which catalyzes the hydrolysis of beta-1,4 N-acetylglucosamine linkages of the fungal cell wall polymer chitin, is a component of the inducible defenses of plants. We show that chitinase synthesis is stimulated in bean (Phaseolus vulgaris L.) cell suspension cultures treated with fungal cell wall elicitors and in hypocotyls in response to infection with the fungus Colletotrichum lindemuthianum. Chitinase cDNA clones were isolated by antibody screening of a lambdagt11 cDNA library containing sequences complementary to poly A(+) RNA from elicited cells. The identity of these clones was confirmed by nucleotide sequence analysis and comparison of the deduced amino acid sequence with that determined for the amino-terminal sequence of bean chitinase. Elicitor causes a very rapid activation of chitinase transcription with a 10-fold stimulation after 5 minutes and 30-fold increase within 20 minutes. This leads to a marked, transient accumulation of chitinase transcripts with maximum levels 2 hours after elicitor treatment, concomitant with the phase of rapid enzyme synthesis. Chitinase transcripts also markedly accumulate in wounded and infected hypocotyls. Chitinase cDNA sequences hybridize to several genomic fragments suggesting there are several chitinase genes in the bean genome.

Organization and differential activation of a gene family encoding the plant defense enzyme chalcone synthase in Phaseolus vulgaris

Chalcone synthase (CHS) catalyzes the first and key regulatory step in the branch pathway of phenylpropanoid biosynthesis specific for synthesis of ubiquitous flavonoid pigments and UV protectants. In bean (Phaseolus vulgaris L.) and other members of the Leguminoseae, chalcone synthase is also involved in the synthesis of the isoflavonoid-derived phytoalexin antibiotics characteristic of this family. We have demonstrated that the haploid genome of bean contains a family of about six to eight CHS genes, some of which are tightly clustered. Treatment of bean cells with fungal elicitor activates several of these genes leading to the accumulation of at least five and probably as many as nine distinct CHS transcripts encoding a set of CHS isopolypeptides of Mr 42-43 kDa but with differing pI in the range pH 6-7. In elicited cells specific transcripts and encoded polypeptides are differentially induced with respect to both the extent and kinetics of accumulation. Wounding or infection of hypocotyl tissue also activates several CHS genes with marked differences in the pattern of accumulation of specific transcripts and encoded polypeptides in wounded compared to infected tissue or elicited cells, indicating operation of more than one cue for defense gene activation. Illumination induces accumulation of a different set of CHS transcripts including only one of the set hitherto demonstrated to be induced by biological stress. The organization and differential regulation of the CHS gene family in bean are discussed in relation to the functions of this enzyme in adaptative and protective responses to diverse environmental stresses.

Rapid induction by fungal elicitor of the synthesis of cinnamyl-alcohol dehydrogenase, a specific enzyme of lignin synthesis

A fivefold increase in the extractable activity of cinnamyl-alcohol dehydrogenase, an enzyme of phenylpropanoid metabolism specific for lignin synthesis, was observed within 10 h of treatment of cell-suspension cultures of bean (Phaseolus vulgaris L.) with a high-molecular-mass elicitor preparation heat-released from mycelial cell walls of the bean pathogen Colletotrichum lindemuthianum. Elicitor caused a rapid, marked but transient increase in the synthesis of cinnamyl-alcohol dehydrogenase with maximum rates 2-3 h after elicitation, concomitant with the phase of rapid increase in enzyme activity. There is a close correspondence between increased polysomal mRNA activity encoding cinnamyl-alcohol dehydrogenase, as measured by incorporation of [35S]methionine into immunoprecipitable enzyme subunits in vitro, and the stimulation of enzyme synthesis in vivo in response to elicitor. This marked increase in polysomal mRNA activity represents an increase as a proportion of total cellular mRNA activity, indicating that elicitor does not stimulate synthesis of this enzyme by selective recruitment from the total pool of cellular mRNA. Elicitor stimulation of cinnamyl-alcohol dehydrogenase activity and enzyme synthesis is more rapid than previously observed for other proteins involved inducible defense mechanisms, such as enzymes of phytoalexin biosynthesis or the apoproteins of cell-wall hydroxyproline-rich glycoproteins.

Elicitor induction of the synthesis of a novel lectin-like arabinosylated hydroxyproline-rich glycoprotein in suspension cultures of Phaseolus vulgaris L

A novel lectin-like glycoprotein which accumulates in response to fungal elicitor action has been characterised in endomembranes from suspension cultures of French bean (Phaseolus vulgaris L.). The lectin, which has specificity towards N-acetylglucosamine oligomers, consists of a polypeptide of apparent molecular weight (Mr) 31 000 which is rich in glycine and contains 6.7% hydroxyproline O-linked to arabinose-containing oligosaccharides to give a glycoprotein of Mr 42500. A dual-labelling technique has been used to identify changes in the synthesis of the glycoprotein in cells exposed to fungal elicitor molecules. Thus, incorporation of [(14)C]proline into membranes in vivo and of [1(-3)H]arabinose from uridine 5'-diphosphate [1(-3)H]arabinose in vitro and analysis by isoelectric focussing-polyacrylamide gel electrophoresis gave absolute correspondence of the labelled isoform of the glycoprotein. Having established the absence of contaminating polypeptides, subsequent analysis of microsomal fractions bysodium dodecyl sulfate-polyacrylamide gel electrophoresis showed that the peak of sythesis of the Mr-42500 glycoprotein occurred 4 h after the addition of fungal elicitor. The changes in the level of incorporation into the glycoprotein monomers were concomitant with increases in the activity of prolyl hydroxylase (EC 1.14.11.2)Incorporation of [(14)C]proline and its subsequent post-translational modification to hydroxyproline in microsomal polypeptides was followed by rapid transfer into the wall with an average t 1/2 of about 7 min. The Mr-42500 glycoprotein was rapidly transferred out of the endomembrane fraction with a t 1/2 of 2 min and could be detected in wall fractions where it became progressively less extractable. The glycoprotein, which clearly differs from bean extensin, accounts for up to 40% of the hydroxyproline newly exported in response to elicitor action. The lectin, which resembles those found in the Solanaceae and which is coinduced with enzymes of phytoalexin synthesis, may play some role in disease resistance.

Oligomerization and the sensitivity of phosphoenolpyruvate carboxylase to inactivation by proteinases

Phosphenolpyruvate (PEP) carboxylase from leaves of Crassula argentea displays varying levels of sensitivity to inactivation by various proteolytic enzymes. In general, the native enzyme is sensitive to proteinases known to attack at the carbonyl end of lysine or arginine (trypsin, papain, or bromelain). The ineffective proteolytic enzymes are those which have low specificity or which attack at the N-terminal end of hydrophobic amino acids, or which cannot attack lysine. The lack of an effect of endoproteinase arginine C, which is specific for arginine, probably indicates that lysine is the critical residue. When the native enzyme, which is comprised of an equilibrium of dimers with tetramers in approximately equal quantities, is treated by preincubation with 5 millimolar PEP, the enzyme becomes much more resistant to proteolytic inactivation. When the preincubation is with 5 millimolar malate rather than buffer alone, the effect is to slightly increase (ca. 15%) the sensitivity of the enzyme to inactivation by trypsin as measured by estimates of the pseudo-first order rate constant for inactivation. PEP carboxylase from corn leaves appears to be relatively susceptible to inactivation by trypsin, but is unaffected by preincubation with malate or PEP. The sensitivity of this C(4) enzyme to inhibition by malate is also unaffected by preincubation with these ligands.

Chitin oligosaccharides as elicitors of chitinase activity in melon plants

Chitin oligosaccharides elicited chitinase activity in melon plants. Hexamer to nonamer were the most efficient elicitors: hexamer for maximal stimulation of colorimetrically assessed chitinase activity, heptamer for maximal stimulation of radiochemically assessed chitinase activity. Chitinase elicitation was a rapid response to these elicitors: it occurred within 6 hours after treatment and was maximal at 12-24 hours. In addition, chitinase induction in melon plants by these oligosaccharides was both local and systemic.