Immunogold localization of beta-1,3-glucanases in two plants infected by vascular wilt fungi

The endophytic strain Fusarium oxysporum Fo47: a good candidate for priming the defense responses in tomato roots

The protective Fusarium oxysporum strain Fo47 is effective in controlling Fusarium wilt in tomato. Previous studies have demonstrated the role of direct antagonism and involvement of induced resistance. The aim of the present study was to investigate whether priming of plant defense responses is a mechanism by which Fo47 controls Fusarium wilt. An in vitro design enabled inoculation of the tap root with Fo47 and the pathogenic strain (Fol8) at different locations and different times. The expression levels of six genes known to be involved in tomato defense responses were quantified using reverse-transcription quantitative polymerase chain reaction (qPCR). Three genes-CHI3, GLUA, and PR-1a-were overexpressed in the root preinoculated with Fo47, and then challenged with Fol8. The genes GLUA and PR-1a were upregulated in cotyledons after inoculation of Fo47. Fungal growth in the root was assessed by qPCR, using specific markers for Fo47 and Fol8. Results showed a reduction of the pathogen growth in the root of the tomato plant preinoculated with Fo47. This study demonstrated that priming of tomato defense responses is one of the mechanisms of action of Fo47, which induces a reduced colonization of the root by the pathogen.

β-1,3-glucanase class III promotes spread of PVYNTN and improves in planta protein production

Glucanases are enzymes regulating the size exclusion limit and permeability of plasmodesmata and play a role in biotic stress. In plant genomes, they are encoded as relatively large gene families divided into four classes. Most studies of plant virus interactions have focused on glucanases from classes I and II. In our study, we have evaluated the role of the β-1,3-glucanase class III (Glu-III) gene in the potato-potato virus Y^NTN (PVY^NTN) interaction and implemented the findings to plant biotechnology application. Potato cultivars Désirée and Santé, which are tolerant and extremely resistant to PVY^NTN, respectively, were stably transformed with Agrobacterium tumefaciens harbouring constructs for Glu-III overexpression. Localization of Glu-III protein in patches within the cell wall was determined by tagging the Glu-III protein with green fluorescent protein. Transgenic and non-transgenic plants were challenged with PVY^NTN and its multiplication and spreading was followed. Differences in viral spread were observed between transgenic lines overexpressing Glu-III and non-transgenic lines, with stronger and faster viral spread in transgenic Désirée, and some multiplication in transgenic Santé. In addition, the ability of Glu-III to improve in planta protein production after agroinfiltration was tested. The results have shown that Glu-III overexpression enables faster spreading of vectors between cells and better protein production, which could be beneficial in improving in planta protein production system using viral vectors.

Transcriptome analysis of quantitative resistance-specific response upon Ralstonia solanacearum infection in tomato

Bacterial wilt, caused by the soil-borne bacterium Ralstonia solanacearum, is a lethal disease of tomato, but the molecular mechanisms of the host resistance responses to R. solanacearum remain unclear. In this study, we report the first work describing the transcriptome of cultivar resistance and susceptible tomato cultivar after inoculation with R. solanacearum. To elucidate the characteristics of resistance early in the interaction, we analyzed microarrays for resistant cultivar LS-89 and susceptible cultivar Ponderosa 1 day after stem inoculation. No change in gene expression was detected for Ponderosa, but expression levels of over 140 genes, including pathogenesis-related, hormone signaling and lignin biosynthesis genes, increased in LS-89. Expression of β-1,3-glucanase genes increased substantially. In an immunohistochemical study, glucanase in LS-89 accumulated in the xylem and pith tissues surrounding xylem vessels filled with R. solanacearum. The expression of these genes also increased in four other resistant cultivars, but changed little in four susceptible cultivars in response to R. solanacearum, suggesting that similar reactions occur in other cultivars. These gene expression profiles will serve as fundamental information to elucidate the molecular mechanisms in the resistance response to R. solanacearum in tomato.

Function of a novel GDSL-type pepper lipase gene, CaGLIP1, in disease susceptibility and abiotic stress tolerance

GDSL-type lipase is a hydrolytic enzyme whose amino acid sequence contains a pentapeptide motif (Gly-X-Ser-X-Gly) with active serine (Ser). Pepper GDSL-type lipase (CaGLIP1) gene was isolated and functionally characterized from pepper leaf tissues infected by Xanthomonas campestris pv. vesicatoria (Xcv). The CaGLIP1 protein was located in the vascular tissues of Arabidopsis root. The CaGLIP1 gene was preferentially expressed in pepper leaves during the compatible interaction with Xcv. Treatment with salicylic acid, ethylene and methyl jasmonate induced CaGLIP1 gene expression in pepper leaves. Sodium nitroprusside, methyl viologen, high salt, mannitol-mediated dehydration and wounding also induced early and transient CaGLIP1 expression in pepper leaf tissues. Virus-induced gene silencing of CaGLIP1 in pepper conferred enhanced resistance to Xcv, accompanied by the suppressed expression of basic PR1 (CaBPR1) and defensin (CaDEF1) genes. The CaGLIP1 lipase produced in Escherichia coli hydrolyzed the substrates of short and long chain nitrophenyl esters. The CaGLIP1-overexpressing Arabidopsis exhibited enhanced hydrolytic activity toward short and long chain nitrophenyl ester, as well as enhanced susceptibility to the bacterial pathogen Pseudomonas syringae pv. tomato and the biotrophic oomycete Hyaloperonospora parasitica. SA-induced expression of AtPR1 and AtGST1, also was delayed in CaGLIP1-overexpressing plants by SA application. During seed germination and plant growth, the CaGLIP1 transgenic plants showed drought tolerance and differential expression of drought- and abscisic acid (ABA)-inducible genes AtRD29A, AtADH and AtRab18. ABA treatment differentially regulated seed germination and gene expression in wild-type and CaGLIP1 transgenic Arabidopsis. Overexpression of CaGLIP1 also regulated glucose- and oxidative stress signaling. Together, these results indicate that CaGLIP1 modulates disease susceptibility and abiotic stress tolerance.

Immunolocalization of a class III chitinase in two muskmelon cultivars reacting differently to Fusarium oxysporum f. sp. melonis

Fusarium oxysporum f. sp. melonis is a highly specialized fungus that attacks the root system of melon (Cucumis melo L.). In this work the presence of a class III chitinase was examined by immunological techniques in the root and stem base of a susceptible (cv. Galia) and a resistant (cv. Bredor) melon during the infection process. By immunolocalization it was not possible to detect the constitutive presence of class III chitinase in any of the cultivars. However, the immunolabelling appeared in the root tissues of both cultivars as a consequence of wounding and of infection by F. oxysporum f. sp. melonis. Distinct patterns of chitinase detection were observed in the roots of the two cultivars as the infection progressed. Furthermore, by western blotting distinct class III chitinase isoforms were detected, which responded differently to the F. oxysporum f. sp. melonis infection. Our results strongly indicate that a relationship exists between class III chitinase and melon resistance to Fusarium infection, and that the resistance is associated with certain isoforms of this enzyme.

Overexpression of a cell wall glycoprotein in Fusarium oxysporum increases virulence and resistance to a plant PR-5 protein

Fusarium oxysporum f. sp. nicotianae is a causal agent for vascular wilt disease in tobacco. It is sensitive to osmotin, a tobacco pathogenesis-related protein (PR-5) that is implicated in plant defense against phytopathogenic fungi. We show that osmotin susceptibility of F. oxysporum f. sp. nicotianae was reduced by overexpression of the heterologous cell wall glycoprotein Saccharomyces cerevisiae protein containing inverted repeats (PIR2), a member of the PIR family of fungal cell wall glycoproteins that protect S. cerevisiae from the toxic action of osmotin. S. cerevisiae PIR2 was targeted to the cell wall of F. oxysporum. Disease severity and fungal growth were increased in tobacco seedlings inoculated with F. oxysporum transformed with PIR2 compared to seedlings infected with untransformed F. oxysporum or that transformed with vector, although accumulation of transcript and protein of defense genes was similar. The results show that fungal cell wall components can increase resistance to plant defense proteins and affect virulence.

Modulation of defense responses of Malus spp. during compatible and incompatible interactions with Erwinia amylovora

Erwinia amylovora is the causal agent of fire blight, a disease affecting members of subfamily Maloideae. In order to analyze mechanisms leading to compatible or incompatible interactions, early plant molecular events were investigated in two genotypes of Malus with contrasting susceptibility to fire blight, after confrontation with either E. amylovora or the incompatible tobacco pathogen Pseudomonas syringae pv. tabaci. Many defense mechanisms, including generation of an oxidative burst and accumulation of pathogenesis-related proteins, were elicited in both resistant and susceptible genotypes by the two pathogens at similar rates and according to an equivalent time course. This elicitation was linked with the functional hypersensitive reaction and pathogenicity (hrp) cluster of E. amylovora, because an hrp secretion mutant did not induce such responses. However, a delayed induction of several genes of various branch pathways of the phenylpropanoid metabolism was recorded in tissues of the susceptible genotype challenged with the wild-type strain of E. amylovora, whereas these genes were quickly induced in every other plant-bacteria interaction, including interactions with the hrp secretion mutant. This suggests the existence of hrp-independent elicitors of defense in the fire blight pathogen as well as hrp-dependant mechanisms of suppression of these nonspecific inductions.

Mass spectrometric identification of isoforms of PR proteins in xylem sap of fungus-infected tomato

The protein content of tomato (Lycopersicon esculentum) xylem sap was found to change dramatically upon infection with the vascular wilt fungus Fusarium oxysporum. Peptide mass fingerprinting and mass spectrometric sequencing were used to identify the most abundant proteins appearing during compatible or incompatible interactions. A new member of the PR-5 family was identified that accumulated early in both types of interaction. Other pathogenesis-related proteins appeared in compatible interactions only, concomitantly with disease development. This study demonstrates the feasibility of using proteomics for the identification of known and novel proteins in xylem sap, and provides insights into plant-pathogen interactions in vascular wilt diseases.

An antifungal protein from the marine bacterium streptomyces sp. Strain AP77 is specific for Pythium porphyrae, a causative agent of red rot disease in Porphyra spp

A novel antifungal protein (SAP) was found in the culture supernatant of a marine bacterium, Streptomyces sp. strain AP77, and was purified. This protein was characterized by chemical, biochemical, and biological analyses. By using gel filtration, the molecular mass of SAP was estimated to be 160 kDa. Structural analysis of SAP by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and matrix-assisted laser desorption ionization-time of flight mass spectrometry suggested that SAP is composed of three heterologous protein subunits of 41.7 kDa (SAP1), 21.7 kDa (SAP2), and 18.7 kDa (SAP3) at a molar ratio of 1:1:5 (or 1:1:6). N-terminal amino acid sequence analysis and a homology search revealed that SAP1, SAP2, and SAP3 exhibit 64.3, 68.4, and 86.7% similarity to three Streptomyces coelicolor polypeptides, puromycin resistance protein (Pur8), a conserved hypothetical protein, and bacterioferritin, respectively. The MIC of purified SAP against Pythium porphyrae was determined to be 1.6 microg/disk, whereas no inhibitory effect was observed at concentrations up to 100 microg/disk against most of the fungal and bacterial strains tested; the only exception was relatively strong antifungal activity against Pythium ultimum (MIC, 6.3 microg/disk). In vitro and in vivo toxicity tests demonstrated that SAP showed no toxicity against Porphyra yezoensis cells, human normal dermal fibroblasts, and mice at doses up to 700 microg/ml (for 24 h), 250 microg/ml (for 12 h), and 75 mg/kg (for 35 days), respectively. SAP was labile when it was subjected to a heated-air drying treatment, which is a great advantage in food production procedures. These results indicated that Streptomyces sp. strain AP77 might be useful as a gene source for safe transgenic Porphyra breeding for tolerance to Pythium infection.

Isolation and characterization of an Arabidopsis thaliana gene for the 54 kDa subunit of the signal recognition particle

The first step in the routing of newly synthesized proteins into the secretory pathway is the binding of the nascent signal sequence to the signal recognition particle. The mammalian signal recognition particle is a complex consisting of 6 proteins and a single 7S RNA molecule. Signal recognition particle-like complexes have been described from wheat and maize but none of the protein components have yet been described from any plant species. Here we report the cloning and characterization of an Arabidopsis thaliana gene encoding the 54 kDa protein subunit of the signal recognition particle. This is the first report of a SRP-54 sequence for any plant species and the first genomic sequence for any multicellular organism.

Nonhost resistance genes and race-specific resistance

Apart from physical barriers, plants have two major types of defense against potential pathogens. In 'race-specific' resistance, plants match single mendelian resistance genes with the 'avirulence' genes possessed by races of a pathogen. Plants also employ the more complex and evolutionarily more robust system of 'nonhost resistance' against a broad range of pathogenic species. In peas, both types of resistance are associated with the expression of a common group of 'resistance response' genes.

Plant 'pathogenesis-related' proteins and their role in defense against pathogens

The hypersensitive reaction to a pathogen is one of the most efficient defense mechanisms in nature and leads to the induction of numerous plant genes encoding defense proteins. These proteins include: 1) structural proteins that are incorporated into the extracellular matrix and participate in the confinement of the pathogen; 2) enzymes of secondary metabolism, for instance those of the biosynthesis of plant antibiotics; 3) pathogenesis-related (PR) proteins which represent major quantitative changes in soluble protein during the defense response. The PRs have typical physicochemical properties that enable them to resist to acidic pH and proteolytic cleavage and thus survive in the harsh environments where they occur: vacuolar compartment or cell wall or intercellular spaces. Since the discovery of the first PRs in tobacco many other similar proteins have been isolated from tobacco but also from other plant species, including dicots and monocots, the widest range being characterized from hypersensitively reacting tobacco. Based first on serological properties and later on sequence data, the tobacco PRs have been classified in five major groups. Group PR-1 contains the first discovered PRs of 15-17 kDa molecular mass, whose biological activity is still unknown, but some members have been shown recently to have antifungal activity. Group PR-2 contains three structurally distinct classes of 1,3-beta-glucanases, with acidic and basic counterparts, with dramatically different specific activity towards linear 1,3-beta-glucans and with different substrate specificity. Group PR-3 consists of various chitinases-lysozymes that belong to three distinct classes, are vacuolar or extracellular, and exhibit differential chitinase and lysozyme activities. Some of them, either alone or in combination with 1,3-beta-glucanases, have been shown to be antifungal in vitro and in vivo (transgenic plants), probably by hydrolysing their substrates as structural components in the fungal cell wall. Group PR-4 is the less studied, and in tobacco contains four members of 13-14.5 kDa of unknown activity and function. Group PR-5 contains acidic-neutral and very basic members with extracellular and vacuolar localization, respectively, and all members show sequence similarity to the sweet-tasting protein thaumatin. Several members of the PR-5 group from tobacco and other plant species were shown to display significant in vitro activity of inhibiting hyphal growth or spore germination of various fungi probably by a membrane permeabilizing mechanism.(ABSTRACT TRUNCATED AT 400 WORDS)

Ethylene-induced chitinase and β-1,3-glucanase accumulate specifically in the lower epidermis and along vascular strands of bean leaves

We have studied the spatial pattern of accumulation of chitinase (EC 3.2.1.14) and β-1,3-glucanase (EC 3.2.1.39) in ethylene-treated leaves of bean (Phaseolus vulgaris L.). Electron-microscopical examination of chemically fixed tissue demonstrated the presence of large electron-dense aggregates in the vacuoles of ethylene-treated leaf cells. No such vacuolar structures were observed in untreated control cells. Immunogold labelling with antisera directed against the basic forms of chitinase and β-1,3-glucanase indicated that the vacuolar aggregates were the major site of accumulation of chitinase and β-1,3-glucanase. The chitinase- and β-1,3-glucanase-containing vacuolar aggregates were not randomly distributed within the leaf tissue but were restricted to the lower epidermal cells and to parenchyma cells adjacent to vascular strands. In addition, heavy β-1,3-glucanase labelling was observed over spongy plugs of expanded middle-lamella material that appear to occlude the transition regions between the airspaces underlying the stomata and those throughout the rest of the leaf. Some labelling was also seen to extend along the surface layer of the cell walls lining all of the airspaces. Protein analysis by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunoblotting as well as enzyme-activity measurements showed that the peeled lower epidermis of the ethylene-treated leaves contained on a protein and on a per-weight basis several times more chitinase and β-1,3-glucanase than the remainder of the leaf.

Accumulation of beta-Fructosidase in the Cell Walls of Tomato Roots following Infection by a Fungal Wilt Pathogen

Active defense in plants is associated with marked metabolic alterations, but little is known about the exact role of the reported changes in specific activity of several enzymes in infected plant tissues. beta-Fructosidase (invertase), the enzyme that converts sucrose into glucose and fructose, increases upon infection by fungi and bacteria. To understand the relationship between fungal growth and beta-fructosidase accumulation, we used an antiserum raised against a purified deglycosylated carrot cell wall beta-fructosidase to study by immunogold labeling the spatial and temporal distribution of the enzyme in susceptible and resistant tomato (Lycopersicon esculentum) root tissues infected with the necrotrophic fungus, Fusarium oxysporum f. sp. racidis-lycopersici. In susceptible plants, the enzyme started to accumulate in host cell walls about 72 hours after inoculation. Accumulation occurred only in colonized cells and was mainly restricted to areas where the walls of both partners contacted each other. In resistant plants, accumulation of beta-fructosidase was noticeable as soon as 48 hours after inoculation and appeared to reach an optimum by 72 hours after inoculation. Increase in wall-bound beta-fructosidase was not restricted to infected cells but occurred also, to a large extent, in tissues that remained uncolonized during the infection process. The enzyme also accumulated in wall appositions (papillae) and intercellular spaces. This pattern of enzyme distribution suggests that induction of beta-fructosidase upon fungal infection is part of the plant's defense response. The possible physiological role(s) of this enzyme in infected tomato plants is discussed in relation to the high demand in energy and carbon sources during pathogenesis.

Time-course study of the accumulation of hydroxyproline-rich glycoproteins in root cells of susceptible and resistant tomato plants infected by Fusarium oxysporum f. sp. radicis-lycopersici

The accumulation of hydroxyproline-rich glycoproteins (HRGPs) in cell walls of dicotyledonous plants is thought to be involved in the defense response to pathogens. An antiserum raised against deglycosylated HRGPs from melon was used for studying the subcellular localization of these glycoproteins in susceptible and resistant tomato (Lycopersicon esculentum Mill.) root tissues infected by Fusarium oxysporum f.sp. radicis-lycopersici. A time-course of HRGP accumulation revealed that these glycoproteins increased earlier and to a higher extent in resistant than in susceptible cultivars. In the compatible interaction, increase in HRGPs was largely correlated with pathogen invasion and appeared to occur as a result of wall damage. In the incompatible interaction, HRGPs accumulated in the walls of uninvaded cells, thus indicating a possible role in the protection against fungal penetration. The occurrence of substantial amounts of HRGPs in papillae, known to be physical barriers formed in response to infection, and in intercellular spaces provides additional support to the concept that such glycoproteins play an important role in disease resistance.

Induction of Arabidopsis defense genes by virulent and avirulent Pseudomonas syringae strains and by a cloned avirulence gene

We developed a model system to study the signal transduction pathways leading to the activation of Arabidopsis thaliana genes involved in the defense against pathogen attack. Here we describe the identification and characterization of virulent and avirulent Pseudomonas syringae strains that elicit disease or resistance symptoms when infiltrated into Arabidopsis leaves. The virulent and avirulent strains were characterized by determining growth of the pathogen in Arabidopsis leaves and by measuring accumulation of mRNA corresponding to Arabidopsis phenylalanine ammonia-lyase (PAL), beta-1,3-glucanase (BG), and chalcone synthase (CHS) genes in infected leaves. The virulent strain, P. syringae pv maculicola ES4326, multiplied 10(5)-fold in Arabidopsis leaves and strongly elicited BG1, BG2, and BG3 mRNA accumulation but had only a modest effect on PAL mRNA accumulation. In contrast, the avirulent strain, P. syringae pv tomato MM1065, multiplied less than 10-fold in leaves and had only a minimal effect on BG1, BG2, and BG3 mRNA accumulation, but it induced PAL mRNA accumulation. No accumulation of CHS mRNA was found with either ES4326 or MM1065. We also describe the cloning of a putative avirulence (avr) gene from the avirulent strain MM1065 that caused the virulent strain ES4326 to grow less well in leaves and to strongly elicit PAL but not BG1 and BG3 mRNA accumulation. These results suggest that the Arabidopsis PAL and BG genes may be activated by distinct signal transduction pathways and show that differences in plant gene induction by virulent and avirulent strains can be attributed to a cloned presumptive avr gene.

Extracellular beta-1,3-Glucanases in Stem Rust-Affected and Abiotically Stressed Wheat Leaves : Immunocytochemical Localization of the Enzyme and Detection of Multiple Forms in Gels by Activity Staining with Dye-Labeled Laminarin

Endo-beta-1,3-glucanase activity in intercellular washing fluid (IWF) from leaves of wheat (Triticum aestivum) increased 10-fold 4 days after leaves were infected with the wheat stem rust fungus (Puccinia graminis f.sp. tritici), while exo-beta-1,3-glucanase activity remained unchanged at a low level. Heat and ethylene stress had no effect, whereas mercury treatment resulted in a 2-fold increase in endo-beta-1,3-glucanase activity. With a new method of activity staining using laminarin-Remazol brilliant blue as substrate in overlay gels, 18 electrophoretic forms of endo-beta-1,3-glucanase were detected in IWF from unstressed leaves and up to 24 forms in IWF from stem rust-infected leaves. Most of the increase in beta-1,3-glucanase activity and in the number of beta-1,3-glucanases after rust infection was due to a nonspecific, stress-related effect on the plant, but two major forms of the enzyme probably originated from the fungus. beta-1,3-Glucanase was localized cytochemically with anti-barley-beta-1,3-glucanase antibodies. With preembedding labeling, the enzyme was demonstrated on the outside of host and fungal cell walls. Postembedding labeling localized the enzyme in the host plasmalemma and in the domain of host cell walls adjoining the plasmalemma, throughout walls of intercellular hyphal cells and haustoria, in the fungal cytoplasm, and in the extrahaustorial matrix. Cross-reactivity of beta-1,3-glucanases from wheat and germinated uredospores of the rust fungus with the anti-barley-beta-1,3-glucanase antibodies was confirmed in dot blot assays and on Western blots.

Subcellular Localization of Chitinase and of Its Potential Substrate in Tomato Root Tissues Infected by Fusarium oxysporum f. sp. radicis-lycopersici

Antiserum raised against a tomato (Lycopersicon esculentum Mill.) chitinase (molecular mass of 26 kilodaltons) was used as a probe to study the subcellular localization of this enzyme in tomato root tissues infected with Fusarium oxysporum f. sp. radicis-lycopersici. A time-course experiment revealed that chitinase accumulated earlier in the incompatible interaction than in the compatible one. However, in both systems, chitinase deposition was largely correlated with pathogen distribution. The enzyme was found to accumulate in areas where host walls were in close contact with fungal cells. In contrast, the enzyme could not be detected in vacuoles and intracellular spaces. The substantial amount of chitinase found at the fungus cell surface supports the view of an antifungal activity. However, the preferential association of the enzyme with altered fungal wall areas indicates that chitinase activity is either preceded by the hydrolytic action of other enzymes such as beta-1,3-glucanases or coincides with these enzymes. The possibility that fungal glucans released through the action of beta-1,3-glucanases may act as elicitors of chitinase production is discussed.