Defense and resistance-inducing activities in tobacco of the sulfated beta-1,3 glucan PS3 and its synergistic activities with the unsulfated molecule.

Laminarin, a beta-1,3 glucan with single beta-glucose branches at position 6, was chemically sulfated to produce PS3 with a degree of sulfation of 2.4. PS3 has previously been shown to activate the salicylic acid (SA) signaling pathway in infiltrated tobacco and Arabidopsis thaliana leaf tissues.

Beta-1,3 glucan sulfate, but not beta-1,3 glucan, induces the salicylic acid signaling pathway in tobacco and Arabidopsis.

Sulfate substituents naturally occurring in biomolecules, such as oligosaccharides and polysaccharides, can play a critical role in major physiological functions in plants and animals. We show that laminarin, a beta-1,3 glucan with elicitor activity in tobacco (Nicotiana tabacum), becomes, after chemical sulfation, an inducer of the salicylic acid (SA) signaling pathway in tobacco and Arabidopsis thaliana. In tobacco cell suspensions, the oxidative burst induced by the laminarin sulfate PS3 was Ca2+ dependent but partially kinase independent, whereas laminarin triggered a strickly kinase-dependent oxidative burst.

Metabolic reprogramming in plant innate immunity: the contributions of phenylpropanoid and oxylipin pathways.

In their environment, plants interact with a multitude of living organisms and have to cope with a large variety of aggressions of biotic or abiotic origin. To survive, plants have acquired, during evolution, complex mechanisms to detect their aggressors and defend themselves. Receptors and signaling pathways that are involved in such interactions with the environment are just beginning to be uncovered.

Biological and molecular comparison between localized and systemic acquired resistance induced in tobacco by a Phytophthora megasperma glycoprotein elicitin.

We have compared localized (LAR) and systemic (SAR) acquired resistance induced in tobacco by a hypersensitive response (HR) inducing Phytophthora megasperma glycoprotein elicitin. Three different zones were taken into account: LAR, SAR(T) and SAR(S). The LAR zone was 5-10 mm wide and surrounded the HR lesion.

Sulfated fucan oligosaccharides elicit defense responses in tobacco and local and systemic resistance against tobacco mosaic virus.

Sulfated fucans are common structural components of the cell walls of marine brown algae. Using a fucan-degrading hydrolase isolated from a marine bacterium, we prepared sulfated fucan oligosaccharides made of mono- and disulfated fucose units alternatively bound by alpha-1,4 and alpha-1,3 glycosidic linkages, respectively. Here, we report on the elicitor activity of such fucan oligosaccharide preparations in tobacco.

Scopoletin expression in elicitor-treated and tobacco mosaic virus-infected tobacco plants.

Localized acquired resistance (LAR) characterizes a narrow zone of living cells expressing strong defense responses and surrounding cells undergoing a hypersensitive response (HR). In Samsun NN tobacco plants, tissues undergoing tobacco mosaic virus-induced or elicitor-induced LAR exhibit a strong blue fluorescence under UV light. We have shown that scopoletin and its glucoside, scopolin, accounted for the fluorescence: (1) both compounds were identified after extraction and purification by thin layer and high performance liquid chromatography; (2) there was a strict correlation between the occurrence of fluorescence and accumulation of high amounts of scopoletin; and (3) infiltration of commercial scopoletin caused a similar fluorescence to that occurring in LAR tissues.

Downregulation of a pathogen-responsive tobacco UDP-Glc:phenylpropanoid glucosyltransferase reduces scopoletin glucoside accumulation, enhances oxidative stress, and weakens virus resistance.

Plant UDP-Glc:phenylpropanoid glucosyltransferases (UGTs) catalyze the transfer of Glc from UDP-Glc to numerous substrates and regulate the activity of compounds that play important roles in plant defense against pathogens. We previously characterized two tobacco salicylic acid- and pathogen-inducible UGTs (TOGTs) that act very efficiently on the hydroxycoumarin scopoletin and on hydroxycinnamic acids. To identify the physiological roles of these UGTs in plant defense, we generated TOGT-depleted tobacco plants by antisense expression.

A pharmacological approach to test the diffusible signal activity of reactive oxygen intermediates in elicitor-treated tobacco leaves.

The capacity of H(2)O(2), the most stable of the reactive oxygen species (ROI), to diffuse freely across biological membranes and to signal gene expression suggests that H(2)O(2) could function as a short-lived second messenger diffusing from cell to cell. We tested this hypothesis in tobacco plants treated with a glycoprotein elicitor. Applied at 50 nM, it induces H(2)O(2) accumulation and the hypersensitive response restricted to the infiltrated zone 1 tissue.

[Stimulation of plant natural defenses].

Some defense mechanisms of plants are of the passive type while others are induced after perception of the pathogenic microorganism (very specific gene-for-gene recognition) or of microbial components (non specific elicitors). These recognition events trigger an array of plant signals and a cascade of signalling pathways which activate a battery of metabolic alterations responsible for the observed induced resistance. These include the stimulated production of low molecular weight molecules with antibiotic activity, cell wall reinforcement by deposition and cross-linking of various macromolecules, and accumulation of a wide range of PR ('pathogenesis-related') proteins that exhibit direct and/or indirect antimicrobial activities.

Free and conjugated benzoic acid in tobacco plants and cell cultures. Induced accumulation upon elicitation of defense responses and role as salicylic acid precursors.

Salicylic acid (SA) is a key endogenous component of local and systemic disease resistance in plants. In this study, we investigated the role of benzoic acid (BA) as precursor of SA biosynthesis in tobacco (Nicotiana tabacum cv Samsun NN) plants undergoing a hypersensitive response following infection with tobacco mosaic virus or in tobacco cell suspensions elicited with beta-megaspermin, an elicitor from Phytophthora megasperma. We found a small pool of conjugated BA in healthy leaves and untreated cell suspensions of tobacco, whereas free BA levels were barely detectable.

Linear beta-1,3 glucans are elicitors of defense responses in tobacco.

Laminarin, a linear beta-1,3 glucan (mean degree of polymerization of 33) was extracted and purified from the brown alga Laminaria digitata. Its elicitor activity on tobacco (Nicotiana tabacum) was compared to that of oligogalacturonides with a mean degree of polymerization of 10. The two oligosaccharides were perceived by suspension-cultured cells as distinct chemical stimuli but triggered a similar and broad spectrum of defense responses.

Hydrogen peroxide from the oxidative burst is neither necessary nor sufficient for hypersensitive cell death induction, phenylalanine ammonia lyase stimulation, salicylic acid accumulation, or scopoletin consumption in cultured tobacco cells treated with elicitin.

H(2)O(2) from the oxidative burst, cell death, and defense responses such as the production of phenylalanine ammonia lyase (PAL), salicylic acid (SA), and scopoletin were analyzed in cultured tobacco (Nicotiana tabacum) cells treated with three proteinaceous elicitors: two elicitins (alpha-megaspermin and beta-megaspermin) and one glycoprotein. These three proteins have been isolated from Phytophthora megasperma H20 and have been previously shown to be equally efficient in inducing a hypersensitive response (HR) upon infiltration into tobacco leaves. However, in cultured tobacco cells these elicitors exhibited strikingly different biological activities.

An early salicylic acid-, pathogen- and elicitor-inducible tobacco glucosyltransferase: role in compartmentalization of phenolics and H2O2 metabolism.

Treatment of tobacco cell suspension cultures with a fungal elicitor of defense responses resulted in an early accumulation of the phenylpropanoid glucosyltransferase TOGT, along with the rapid synthesis and secretion of scopolin, the glucoside of scopoletin. Elicitor-triggered extracellular accumulation of the aglycone scopoletin and of free caffeic and ferulic acids could only be revealed in the presence of diphenylene iodonium, an inhibitor of extracellular H2O2 production. Our results strongly support a role for TOGT in the elicitor-stimulated production of transportable phenylpropanoid glucosides, followed by the release of free antioxidant phenolics into the extracellular medium and subsequent H2O2 scavenging.

Two tobacco genes induced by infection, elicitor and salicylic acid encode glucosyltransferases acting on phenylpropanoids and benzoic acid derivatives, including salicylic acid.

Two tobacco genes (TOGT) with homology to glucosyltransferase genes known to be induced by salicylic acid (SA) also responded rapidly to a fungal elicitor or to an avirulent pathogen. SA, although an efficient inducer, was shown not to be essential in the signal transduction pathway regulating TOGT gene expression during the resistance response. Recombinant TOGT proteins produced in Escherichia coli exhibited low, but significant, glucosyltransferase activity towards SA, but very high activity towards hydroxycoumarins and hydroxycinnamic acids, with glucose esters being the predominant products.

Substrate specificities of tobacco chitinases.

Ten tobacco chitinases (1,4-N-acetyl-beta-D-glucosaminide glycanhydrolase, EC 3.2.1.

Antimicrobial proteins in induced plant defense.

During the past few years a wide spectrum of plant antimicrobial proteins has been detailed, and enhanced resistance has been obtained by introducing the corresponding genes into crop species to produce transgenic lines. With the aim of manipulating the plant signals that regulate an array of defense responses, the most intense research focuses on the avr-R-mediated recognition events and elucidation of the subsequent signaling pathways that govern the activation of genes encoding antimicrobial proteins.

Expression of class I O-methyltransferase in healthy and TMV-infected tobacco.

Tobacco possesses two distinct classes of O-methyltransferases (OMTs; S-adenosyl-L-methionine:o-diphenol O-methyltransferases; EC 2.1.1.

A new elicitor of the hypersensitive response in tobacco: a fungal glycoprotein elicits cell death, expression of defence genes, production of salicylic acid, and induction of systemic acquired resistance.

A 32 kDa glycoprotein whose effects in tobacco and other Nicotianae mimic a typical hypersensitive response, was isolated from Phytophthora megasperma. Infiltration of a few nanograms of the protein into leaves caused the formation of lesions that closely resemble hypersensitive response lesions. Transcripts of genes encoding enzymes of the phenylpropanoid and sesquiterpenoid pathways accumulated rapidly after elicitor application followed by salicylic acid production.

Structural features of fungal beta-D-glucans for the efficient inhibition of the initiation of virus infection on Nicotiana tabacum.

Glucans of fungal origin have been shown to inhibit the early stages of infection of Nicotiana by numerous viruses of different taxonomic groups. Several glucans were isolated from the cell walls of Phytophthora parasitica, Phytophthora megasperma f. sp.

Pathogenesis-related PR-1 proteins are antifungal. Isolation and characterization of three 14-kilodalton proteins of tomato and of a basic PR-1 of tobacco with inhibitory activity against Phytophthora infestans.

Three distinct basic 14-kD proteins, P14a, P14b, and P14c, were isolated from tomato (Lycopersicon esculentum Mill. cv Baby) leaves infected with Phytophthora infestans. They exhibited antifungal activity against P.

Phenylalanine ammonia-lyase in tobacco. Molecular cloning and gene expression during the hypersensitive reaction to tobacco mosaic virus and the response to a fungal elicitor.

A tobacco (Nicotiana tabacum L. cv Samsun NN) cDNA clone coding the enzyme phenylalanine ammonia-lyase (PAL) was isolated from a cDNA library made from polyadenylated RNA purified from tobacco mosaic virus (TMV)-infected leaves. Southern analysis indicated that, in tobacco, PAL is encoded by a small family of two to four unclustered genes.

Molecular characterization of a novel tobacco pathogenesis-related (PR) protein: a new plant chitinase/lysozyme.

A new PR (pathogenesis-related) protein was isolated from tobacco leaves (Nicotiana tabacum cv. Samsun NN), reacting hypersensitively to tobacco mosaic virus (TMV), by zinc chelate chromatography and was therefore named Pz. Its reactivity toward several lectins indicated the presence of bound sugar residues.

One-step purification and characterization of a lignin-specific O-methyltransferase from poplar.

O-Methyltransferases (OMT; EC 2.1.1.

Molecular cloning and expression of a new class of ortho-diphenol-O-methyltransferases induced in tobacco (Nicotiana tabacum L.) leaves by infection or elicitor treatment.

In tobacco (Nicotiana tabacum L. cv Samsun NN), three distinct enzymes account for ortho-diphenol-O-methyltransferase (OMT) activity. OMT I is the major enzyme of healthy leaves, whereas enzymes OMT II and III are preferentially induced during the hypersensitive reaction to tobacco mosaic virus (TMV).

cDNA cloning and gene expression analysis of the microbial proteinase inhibitor of tobacco.

Tobacco mosaic virus-infected tobacco (Nicotiana tabacum var. Samsun NN) leaves produce a serine proteinase inhibitor that has evolved a specificity for microbial proteinases. We have isolated two closely related cDNAs that were shown to encode two active inhibitors.