Leaf-specific thionins of barley-a novel class of cell wall proteins toxic to plant-pathogenic fungi and possibly involved in the defence mechanism of plants

Hordothionins inhibit protein synthesis at the level of initiation in the wheat-germ system

The inhibitory effect of pure alpha and beta hordothionins on protein synthesis directed by pea mRNA has been studied in the wheat-germ translation system. It is demonstrated that a component of the wheat germ counteracts the thionin effect. Formation of polysomes in vitro in the presence of thionin was inhibited to the same extent as the total translation system while run-off translation of isolated polysomes from pea plants was not affected by thionin. These data are consistent with an effect of thionin on the initiation reaction. Analyses of the formation of initiation complexes in the presence and absence of mRNA support this view and show that thionin interferes with the formation of the 43S complex. In accordance with this observation and in contrast to earlier studies no evidence has been obtained for a direct interaction between mRNAs and thionins. The analysis of the translation products also gave no indication for preferential translation of individual mRNAs by the thionin-inhibited translation system. Compared to translation in vitro, exposure of barley protoplasts to thionins showed a less dramatic effect on protein synthesis as measured by incorporation of [35S]methionine into proteins. These data are discussed with respect to the effects of thionins on the plasma membranes as shown previously with animal cell cultures. It is concluded that at least in barley such effects would need higher concentrations of thionins than are required for the inhibition of protein synthesis.

Expression of biologically active hordothionins in tobacco. Effects of pre- and pro-sequences at the amino and carboxyl termini of the hordothionin precursor on mature protein expression and sorting

Hordothionins (HTHs) are small anti-bacterial proteins present in barley endosperm which are processed from larger precursor proteins, consisting of an amino-terminal signal peptide (SP), the mature highly basic HTH and a carboxy-terminal acidic peptide (AP). Different HTH precursor proteins were expressed in tobacco to study the effects of the pre-sequences (SP) and pro-sequences (AP) on expression, processing, sorting and biological activity and hence the feasibility of engineering bacterial disease resistance into crops which lack these proteins. Maximum HTH expression levels of approximately 0.7% (11 mumol/kg) of total soluble protein in young tobacco leaves were obtained using a semi-synthetic gene construct encoding a complete chimaeric HTH precursor protein. Tenfold lower HTH expression levels (maximum 1.3 mumol/kg) were obtained using synthetic gene constructs without the AP-coding sequence and no expression was found in plants containing synthetic HTH gene constructs without SP- and AP-coding sequences. In both cases where expression was found, the precursors were apparently correctly processed, although the HTH produced in plants containing a construct without AP sequence appeared to be slightly modified. No effect on plant phenotype was observed. Localization studies indicated that the HTH was in identical fractions of plants expressing the two different precursors, albeit at a different ratio, and was not secreted into the intercellular spaces of leaves or culture medium by protoplasts. Our results indicated that the AP is not involved in sorting and suggested that it might facilitate transport through membranes. The in vitro toxicity of HTH isolated from transgenic tobacco plants expressing the two different precursor proteins for the bacterial plant pathogen Clavibacter michiganensis subsp. michiganensis appeared similar to that of the HTH purified from barley endosperm.

cDNA-derived identification of novel thionin precursors in Viscum album that contain highly divergent thionin domains but conserved signal and acidic polypeptide domains

The existence of new thionin variants in Viscum album has been deduced from cDNA sequences. Unlike the viscotoxins and related thionins previously found in different members of the Viscaceae, these novel thionins contain eight rather than six cysteine residues. In this respect they resemble thionins described previously from various cereals and from Pyrularia pubera, which also contain eight cysteine residues at identical positions. All of the new thionins of V. album are encoded as higher-molecular-weight precursors consisting of a signal peptide, a thionin domain and an acidic polypeptide domain. While the deduced amino acid sequences of the thionin domains of different precursor molecules are highly divergent, the two other domains are conserved among all of the variants and are distinct from the corresponding domains of thionin precursors of other plant species.

A novel fingerprint method for analyzing the expression of complex multigene families of very low transcript abundance

A novel RNA fingerprint method has been developed based on the polymerase chain reaction to identify individual mRNA species derived from different members of a complex multigene family of very low transcript abundance. Using this method, changes in the composition of complex thionin mRNA populations and in the appearance of individual thionin mRNA species in different organs and in response to external stimuli were detected in Hordeum murinum. A single nucleotide exchange within the transcribed DNA may be sufficient to allow the distinction between otherwise identical transcripts.

Effect of Jasmonic Acid on the Interaction of Barley (Hordeum vulgare L.) with the Powdery Mildew Erysiphe graminis f.sp. hordei

Jasmonic acid or its methyl ester induce de novo synthesis of a number of proteins of mostly unknown function in barley (Hordeum vulgare L.). In a topical spray application, 30 [mu]g of jasmonic acid per plant effectively protected barley against subsequent infection by Erysiphe graminis f.sp. hordei. Examination of jasmonic acid-induced barley proteins revealed the presence of several acid-soluble (pH 2.8) proteins. Two prominent groups of 25 kD and 10 to 12 kD apparent molecular mass were present in the intercellular washing fluid. The set of extracellular, induced proteins showed no similarity to barley pathogenesis-related proteins. An in vivo test against E. graminis revealed no antifungal activity of the extracellular jasmonic acid-induced proteins. Experiments with the transcription inhibitor cordycepin showed no correlation between accumulation of jasmonic acid-induced proteins and protection. The application of jasmonic acid and E. graminis simultaneously resulted in independent extracellular accumulation of both jasmonic acid-induced proteins and of pathogenesis-related proteins. The data suggest that jasmonic acid directly inhibits appressoria differentiation of the fungus, and that it is not involved in the signal transduction mechanism leading to induction of pathogenesis-related proteins.

The barley alpha-thionin promoter is rich in negative regulatory motifs and directs tissue-specific expression of a reporter gene in tobacco

The promoter of the barley alpha-thionin gene (1.6 kb) fused to the beta-glucuronidase (GUS) gene directs temporally-controlled, tissue-specific expression in the endosperm of transgenic tobacco. The nucleotide sequence of this promoter shows negative regulatory motifs which have been functionally analyzed in other genes.

The Anticyclic Timing of Leaf Senescence in the Parasitic Plant Viscum album Is Closely Correlated with the Selective Degradation of Sulfur-Rich Viscotoxins

Leaf senescence and abscission have been studied in the semi-parasitic plant mistletoe (Viscum album). Leaf senescence and abscission occur in the summer, when the metabolic activity of the host has reached its maximum. In contrast with their hosts, mistletoes selectively degrade only one major leaf protein during leaf senescence, the sulfur-rich viscotoxin, whereas most of the remaining leaf proteins are lost during abscission. The changes in viscotoxin content are paralleled by changes in the concentration of the corresponding mRNA. Shortly before the onset of leaf senescence, the mRNA for viscotoxin has disappeared from the leaves. The anticyclic timing of leaf senescence and the degradation of only one major leaf protein seems to reflect an adaptation of the parasite to its habitat.

A non-specific lipid transfer protein from Arabidopsis is a cell wall protein

Lipid transfer proteins (LTPs), mediate the transfer of phospholipids between membranes in vitro. However, the in vivo function of LTPs is not known. To determine the precise location of a non-specific LTP from Arabidopsis, a cDNA clone was used to produce an Arabidopsis LTP:protein A fusion. Antibodies raised against the fusion were used to localize the Arabidopsis LTP by immunoelectron microscopy. LTP was found to be located in the cell wall, mainly in epidermal cells. This location appears to be inconsistent with the proposed role of the protein in intracellular lipid transfer.

Expression of the alpha-thionin gene from barley in tobacco confers enhanced resistance to bacterial pathogens

Thionins are cysteine-rich, 5 kDa polypeptides which are toxic to plant pathogens in vitro. Expression of the gene encoding alpha-thionin from barley endosperm, under the 35S promoter from cauliflower mosaic virus, conferred to transgenic tobacco enhanced resistance to the bacterial plant pathogens Pseudomonas syringae pv. tabaci 153 and P. syringae pv. syringae. The barley alpha-thionin gene, which has two introns, was correctly spliced in tobacco. The alpha-thionin in transgenic plants had the expected mobility in the gradient, when separated by high-performance liquid chromatography, reacted with monospecific antibodies and showed the expected antibiotic properties in vitro.

Solution structure of gamma 1-H and gamma 1-P thionins from barley and wheat endosperm determined by 1H-NMR: a structural motif common to toxic arthropod proteins

The complete assignment of the proton NMR spectra of the homologous gamma 1-hordothionin and gamma 1-purothionin (47 amino acids, 4 disulfide bridges) from barley and wheat, respectively, has been performed by two-dimensional sequence-specific methods. A total of 299 proton-proton distance constraints for gamma 1-H and 285 for gamma 1-P derived from NOESY spectra have been used to calculate the three-dimensional solution structures. Initial structures have been generated by distance geometry methods and further refined by dynamical simulated annealing calculations. Both proteins show identical secondary and tertiary structure with a well-defined triple-stranded antiparallel beta-sheet (residues 1-6, 31-34, and 39-47), an alpha-helix (residues 16-28), and the corresponding connecting loops. Three disulfide bridges are located in the hydrophobic core holding together the alpha-helix and the beta-sheet and forming a cysteine-stabilized alpha-helical (CSH) motif. Moreover, a clustering of positive charges is observed on the face of the beta-sheet opposite to the helix. The three-dimensional structures of the gamma-thionins differ remarkably from plant alpha- and beta-thionins and crambin. However, they show a higher structural analogy with scorpion toxins and insect defensins which also present the CSH motif.

The effect of heat shock on morphogenesis in barley : coordinated circadian regulation of mRNA levels for light-regulated genes and of the capacity for accumulation of chlorophyll protein complexes

The effect of daily heat-shock treatments on gene expression and morphogenesis of etiolated barley (Hordeum vulgare) was investigated. Heat-shock treatments in the dark induced shortening of the primary leaves and the coleoptiles to the length of those in light-grown plantlets. In addition, the mRNA levels of the light-induced genes that were investigated were raised under these conditions and showed distinct oscillations over a period of at least 3 d. While the mRNA levels for chlorophyll a/b binding protein (LHC II), plastocyanin, and the small subunit of ribulose-1,5-bisphosphate carboxylase had maxima between 8 and 12 pm (12-16h after the last heat-shock treatment), the mRNA levels for thionin oscillated with a phase opposed to that of LHC II. Etiolated barley, the circadian oscillator of which was synchronized by cyclic heatshock treatments, was illuminated for a constant interval at different times of the day; this led to the finding that greening was fastest at the time when the maximal levels of mRNA for LHC II were also observed. Whereas accumulation of chlorophyll a during a 4-h period of illumination oscillated by a factor of 3, chlorophyll b accumulation changed 10- to 15-fold. Similarly, accumulation of LHC II was highest when pigments accumulated maximally. Hence, greening or, in other words, thylakoid membrane assembly is under control of the circadian oscillator.

Purification of maize pollen exines and analysis of associated proteins

Zea mays (maize) pollen exines have been purified with the use of differential centrifugation and sucrose gradients, followed by mild detergent and high salt treatment. The final exine fraction is highly purified from other organelles and subcellular structures as assayed by transmission electron microscopy. Using mature maize pollen as the starting material, 0.2 to 0.3% of the total pollen protein remained associated with the exine fraction throughout the purification. Seven abundant sodium dodecyl sulfate-extractable proteins are detected by sodium dodecyl sulfate-polyacrylamide gel electrophoresis in the final fraction. Amino acid analysis reveals that one of the proteins contains a substantial amount of hydroxyproline, a characteristic of some primary cell wall proteins. The amino acid composition of the 25-kD protein strongly implies that it is an arabinogalactan protein. When exines are purified from earlier pollen developmental stages, a subset of the proteins found in the mature pollen exine is seen.

Roles for the extracellular matrix in plant development and pollination: a special case of cell movement in plants

Pattern formation in plants is now thought to be primarily dependent on positional information during development. We discuss the prevalent theories on how position is deciphered by cells in an organism and highlight the recent advances implicating molecules of the cell wall or extracellular matrix (ECM) in this process. We compare the functions of the ECM in plants and animals and describe the various cell and substrate adhesion molecules of the animal ECM which play a role in morphogenesis and cell movement. We propose that analogous molecules may occur in plants and provide evidence for the presence of a substrate adhesion molecule like vitronectin in plants and algae. We provide a model for how substrate adhesion molecules may be involved in a special case of cell movement in plants, pollination.

Elicitor- and wound-induced oxidative cross-linking of a proline-rich plant cell wall protein: a novel, rapid defense response

Treatment of bean or soybean cells with fungal elicitor or glutathione causes a rapid insolubilization of preexisting (hydroxy)proline-rich structural proteins in the cell wall. This insolubilization, which involves H2O2-mediated oxidative cross-linking, is initiated within 2 min and is complete within 10 min under optimal conditions, and hence, precedes the expression of transcription-dependent defenses. Cross-linking is also under developmental control during hypocotyl growth and in tissues subject to mechanical stress such as the stem-petiole junction. Stimulus-dependent oxidative cross-linking of wall structural proteins is a novel site of cellular regulation with potentially important functions in cell maturation and toughening of cell walls in the initial stages of plant defense.

A flower-specific cDNA encoding a novel thionin in tobacco

We isolated a flower-specific cDNA, FST (flower-specific thionin), which encodes a novel thionin from tobacco. Thionins are basic and cysteine (Cys)-rich, low molecular weight proteins found in many plants. They are believed to play a role in plant defense against pathogens. The central domain of the FST protein shares homology with three gamma-thionins. Like other thionin precursors, the FST protein has an N-terminal domain characteristic of a signal peptide and an acidic C-terminal domain. FST mRNA accumulates specifically in developing flowers and its level drops as flowers mature. Transcripts are present in petals, stamens and pistil but are not detectable in sepals. In situ hybridization revealed that FST mRNA is most abundant in the epidermal cells along the adaxial surface of petals, and in the surface cell layers of the carpel and anther walls. If the FST protein indeed has a protective role in flowers, this pattern of spatial distribution of FST mRNA would appear to maximize this effect on the two internal reproductive whorls. A possible biological role for FST is discussed.

Extreme divergence of a novel wheat thionin generated by a mutational burst specifically affecting the mature protein domain of the precursor

A new type of neutral thionin (type V), specifically expressed in developing wheat endosperm, has been found to be encoded by a set of single-copy genes located in the long arms of chromosomes 1A, 1B and 1D, within less than 10,000 base-pairs of those corresponding to the highly basic type-I thionins. Divergence between types I and V has occurred through a process of accelerated evolution that has affected the amino acid sequence of the mature thionin but not the precursor domains corresponding to the N-terminal signal peptide and the long C-terminal acidic peptide. This process involved a deletion and a non-synonymous nucleotide substitution rate equal to the synonymous rate in the thionin sequence.

A comparison of leaf thionin sequences of barley cultivars and wild barley species

Leaf thionins of several barley cultivars and wild barley species were analysed. We found large differences in the numbers of leaf thionin genes in different Hordeum species. While, for instance, cultivars of Hordeum vulgare (Section Hordeum) contain more than 50 copies of thionin genes per haploid genome, the numbers are much lower in Hordeum species belonging to the sections Critesion and Stenostachys. The apparent number of genes correlates with the concentration of leaf thionin and its mRNA, which differs more than 100-fold among various Hordeum species. Leaf thionins are synthesized as high molecular weight precursor proteins that contain a signal peptide domain, a thionin domain and an acidic polypeptide domain. Analysis of cDNA clones of leaf thionins revealed a family of related transcripts. When the predicted amino acid sequences of the precursor molecules of wild barley species were compared, differences in the sequence variability of the three domains became apparent. The frequency of amino acid exchanges is much higher within the thionin domain than in the signal peptide and acidic polypeptide domains. The amino acid exchanges within the thionin domain do not occur at random but are confined to variable regions that alternate with highly conserved areas. Conserved regions comprise mostly cysteine residues and adjacent amino acids and may be important for the correct formation of the specific disulphide configuration of thionins.

Effects of thionins on beta-glucuronidase in vitro and in plant protoplasts

Thionins cause the irreversible inactivation of beta-glucuronidase (GUS) in vitro in a dose- and time-dependent manner. The enzyme is also sensitive to externally added thionins when expressed in the cytoplasmic compartment of tobacco protoplasts transformed with the Gus gene under the 35S promoter of the cauliflower mosaic virus. In protoplasts transformed with the Gus gene fused to a signal peptide, where GUS is translocated into the lumen of the endoplasmic reticulum, the activity is significantly increased both by externally-added and by transiently-expressed thionin, suggesting that it interferes with GUS secretion.

Molecular characterization of two stamen-specific genes, tap1 and fil1, that are expressed in the wild type, but not in the deficiens mutant of Antirrhinum majus

Deficiens, a homeotic gene involved in the genetic control of flower development, codes for a putative transcription factor. Upon mutation of the gene, petals are transformed to sepals and stamens to carpels, indicating that deficiens is essential for the activation of genes required for petal and stamen formation. In a search for putative target genes of deficiens, several stamen- and petal-specific genes were cloned that are expressed in wild type but not in the deficiensglobifera mutant. In this report the molecular characterization of two of these genes, tap1 and fil1, is presented. They are transiently expressed during flower development. In situ hybridization data demonstrate that tap1 is expressed in the tapetum of the anthers and fil1 in the filament of the stamen and at the bases of the petals. Both genes encode small proteins with N-terminal hydrophobic domains suggesting that they are secreted. We discuss possible functions of the gene products and their relationship to the deficiens gene.

Amino acid sequence and disulfide bridges of an antifungal protein isolated from Aspergillus giganteus

A very basic secreted protein which displays antifungal activity was isolated from the medium of the mold Aspergillus giganteus. The protein consists of 51 amino acid residues whose sequence was determined as Ala-Thr-Tyr-Asn-Gly-Lys-Cys-Tyr-Lys-Lys-Asp-Asn- Ile-Cys-Lys-Tyr-Lys-Ala-Gln-Ser-Gly-Lys-Thr-Ala-Ile-Cys-Lys-Cys-Tyr-Val- Lys- Lys-Cys-Pro-Arg-Asp-Gly-Ala-Lys-Cys-Glu-Phe-Asp-Ser-Tyr-Lys-Gly-Lys-Cys- Tyr-Cys . Disulfide bonds were formed between Cys7-Cys33, Cys14-Cys40, Cys26-Cys28 and Cys49-Cys51. These results suggest that the antifungal protein forms a loop structure and is similar to phospholipase A2.

5S-RNA genes of barley are located on the second chromosome

The genes coding for 5S RNA in barley were cloned, sequenced, and their cluster was assigned to chromosome 2 using wheat-barley chromosome addition lines. High-resolution gel-electrophoresis of DNA and subsequent hybridization revealed new details of the organization of 5S DNA both in wheat and barley. The in situ hybridization of the cloned 5S gene with triploid endosperm nuclei also suggests that these genes are located in a single locus.

Histochemical localization of cysteine-rich proteins by tissue printing on nitrocellulose

A rapid technique for the histochemical localization of cysteine-rich proteins in plant tissues was developed. It is based on the immediate transfer of proteins to nitrocellulose membranes when a fresh cut organ is pressed against the membrane surface. The print was labeled for cysteine-rich proteins by reduction and alkylation of cysteinyl residues with dansylated iodoacetamide [N-iodoacetyl-N'-(-5-sulfo-1-naphthyl)ethylenediamine]. The S-carboxymethylated proteins were visualized by their fluorescence when excited with 360 nm light.

cis-analysis of the wound-inducible promoter wun1 in transgenic tobacco plants and histochemical localization of its expression

The 5' region of the wound-inducible gene wun1, derived from potato, has been sequenced and analyzed for cis-acting elements important in controlling gene expression in transgenic tobacco plants. Different 5' deletion fragments were linked to the reporter gene beta-glucuronidase (GUS) as transcriptional fusions, and the expression of these chimeric genes was analyzed in leaf tissue. Sequences 111 base pairs upstream of the transcriptional start site were not able to drive the GUS expression over background levels, whereas sequences between -111 and -571 showed a slightly higher activity with equal levels of transcription in wounded and nonwounded tissue. The addition of further upstream sequences (-571 to -1022) enhanced the level of expression by a factor between 13 and 370. The expression driven by this fragment was inducible by a factor of twofold to ninefold by wounding. Histochemical analysis of different tissue from transgenic plants that contain wun1-GUS fusions demonstrates wound-inducible and cell-specific wun1 promoter activity in plants containing the -1022-base pair fragment. The location of GUS activity appears to be cell-specific, being highest in epidermal cells of leaves and stems and lower in vascular cells. Activity was reduced to levels that could not be detected by histochemical staining in leaves, stems, and roots of plants containing the deleted promoter fragments. Plants that contain the different deletion constructs and plants that carry the -1022-base pair fragment show high expression in anthers and pollen grains that could not be stimulated by wounding.

Cultivar-related differences in the distribution of cell-wall-bound thionins in compatible and incompatible interactions between barley and powdery mildew

Leaf-specific thionins of barley (Hordeum vulgare L.) have been identified as a novel class of cell-wall proteins toxic to plant-pathogenic fungi and possibly involved in the defence mechanism of plants. The distribution of these polypeptides has been studied in the host-pathogen system of barley and Erisyphe graminis DC.f.sp. hordei Marchal (powdery mildew). Immunogold-labelling of thionins in several barley cultivars indicates that resistance or susceptibility may be attributed to the presence or absence of thionins at the penetration site in walls and papillae of epidermal leaf cells.All of the leaf-specific thionin genes are confined to the distal end of the short arm of chromosome 6 of barley. None of the genes for cultivarspecific resistance to powdery mildew which have previously been mapped on barley chromosomes are found close to this locus.

The effect of light on the biosynthesis of leaf-specific thionins in barley, Hordeum vulgare

In barley seedlings grown in the dark large amounts of thionin-specific mRNAs are present, the concentration of which rapidly declines once the seedling is exposed to light. This rapid light effect is mediated by a complex interaction of possibly two photoreceptors, phytochrome and a blue-light-absorbing photoreceptor. Parallel to the decline in mRNA content, the de novo synthesis of leaf-specific thionins ceases rapidly upon illumination of etiolated seedlings. However, thionins which have accumulated before the onset of illumination remain stable within the seedling at high concentrations. In younger leaves of mature, nonstressed barley plants grown under a 16-h-light/8-h-dark cycle thionins are still present, although at much lower concentrations. In these plants, synthesis and accumulation of thionins occur predominantly in the meristematic zone at the leaf basis, which is shielded from light through the sheath of the preceding leaf. In mature light-adapted barley plants, mRNA encoding leaf-specific thionins may reaccumulate if these plants are exposed to pathogens or other stresses. Thus, the inhibitory effect of light on the biosynthesis of thionins may be overruled by stress- and pathogen-induced signals.

The effect of chemical stress on the polypeptide composition of the intercellular fluid of barley leaves

The effect of chemical stress on the polypeptide composition of the intercellular fluid of barley (Hordeum vulgare L.) and tomato (Lycopersicon esculentum Mill.) leaves has been studied. In some dicotyledonous plant species, including tomato, exposure to chemical stress leads to the denovo synthesis of intercellular proteins known as pathogenesis-related proteins which have been implicated to be part of a defence mechanism. In barley, however, no such changes in the polypeptide composition of the intercellular fluid could be detected. On the other hand, similar stress conditions induce in barley a strong accumulation of mRNA encoding leaf-specific thionins. These barley thionins represent a novel class of cell-wall proteins toxic to phytopathogenic fungi and are possibly involved in the defence mechanism. These proteins could not be detected in tomato plants. In contrast to the pathogenesis-related proteins of dicotyledonous plants, the leaf-specific thionins of barley are not present in the intercellular fluid of leaves. These results indicate that barley may have evolved a different mechanism to cope with the presence of stress.

A highly conserved Brassica gene with homology to the S-locus-specific glycoprotein structural gene

The S-locus-specific glycoprotein of Brassica and the gene encoding it (the SLG gene) are thought to be involved in determining self-incompatibility phenotype in this genus. It has been shown that the Brassica genome contains multiple SLG-related sequences. We report here the cloning and characterization of a Brassica oleracea gene, SLR1, which corresponds to one of these SLG-related sequences. Like the SLG gene, SLR1 is developmentally regulated. It is maximally expressed in the papillar cells of the stigma at the same stage of flower development as the onset of the incompatibility response. Unlike SLG, the SLR1 genes isolated from different S-allele homozygotes are highly conserved, and this gene, which appears to be ubiquitous in crucifers, is expressed in self-compatible strains as well as self-incompatible strains. Most importantly, we show that the SLR1 gene is not linked to the S-locus and therefore cannot be a determinant of S-allele specificity in Brassica.

5' upstream sequences from the wun1 gene are responsible for gene activation by wounding in transgenic plants

A 1.2-kilobase pair fragment of the 5' upstream region of a potato wound-inducible gene (wun1) was fused to different marker genes (wun1-CAT, wun1-NPTII). Stable integration of a wun1-CAT chimeric gene into the tobacco genome led to a high wound-inducible chloramphenicol acetyltransferase activity in leaves. Transient expression experiments in potato protoplasts showed that wun1 carries a strong promoter sequence similar in strength to the 35S promoter. The same intensity of expression was also observed using wun1 constructs in transient experiments with rice protoplasts. wun1 mRNA was shown to accumulate to high levels in potato leaves collapsing as a result of infection with the phytopathogen Phytophthora infestans. The wun1 product might, therefore, play a role in a general physiological reaction to stress correlated with cell death.