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Looking for a role of polygalacturonase of Fusaria during cereal infection
Full text linkTo penetrate and colonize host tissue most pathogenic fungi produce enzymes degrading the cuticle and the plant cell wall. Among these, pectinases and in particular endo-polygalacturonases (PGs), are expressed in the early stages of host infection and contribute to the virulence or the pathogenicity of several phytopathogenic fungi by degrading the pectin component of the cell wall and middle lamella. Pectic enzymes are considered the main factors responsible for the maceration of the pectin rich cell wall of dicotyledonous plants. Recently, the importance of these enzymes has been shown also in the pathogenesis of some Graminaceous, although these plants have a cell wall consisting of small amount of pectin.
Fusarium graminearum and Fusarium verticillioides are two relevant pathogens of cereal species and are know to produce PG activity in liquid culture. The demonstration that the PGs of these fungi are virulence factors might contribute to develop strategies aimed to increase the resistance of host plants to infection by these pathogens. To clarify the importance of these enzymes during pathogenesis, firstly the two endo-PGs secreted in vitro by F. graminearum were purified and characterized. These PGs showed different biochemical properties, like optimum pH and substrate cleavage mechanism. The expression of their encoding genes was analysed also during wheat infection compared to the expression of pectin lyase and xylanase encoding genes: since pectinases genes were expressed earlier than xylanase gene, pectinases, and in particular PGs, might play a role during the early stage of infection.
To establish the importance in pathogenesis of the two purified and characterized F. graminearum PGs, and of F. verticillioides PG, previously characterized (Sella et al., 2004; Raiola et al., in press), their encoding genes were disrupted by targeted homologous recombination. The pathogenicity of each mutant was tested by inoculating host plants. Single F. graminearum mutants maintained the capability to infect wheat plants. However, since the loss of PG activity due to the knock-out of a single pg gene could be compensated by the activity of the remaining PG, a double knock-out mutant should be obtained and tested in infection experiments. Also the F. verticillioides mutant maintained the capability to infect maize plants, but in this case the pg gene disruption caused a reduction of virulence. In particular, the necrotic symptom observed during infection with the wild-type strain might be related to the presence of the PG in the infected tissue
Expression of two Sclerotinia sclerotiorum endo-PG genes correlates with endo-polygalacturonase activity during Glycine max colonization
Full text linkQuantitative expression of Sclerotinia sclerotiorum genes encoding two endo-polygalacturonase (endo-PG) isoforms (PGa and PGb), malate dehydrogenase (MDH, a key enzyme in fungal biosynthetic pathway of oxalic acid), and plant polygalacturonase-inhibiting protein (PGIP) were monitored by real-time reverse transcription-polymerase chain reaction (qRT-PCR) during the early stages (0-48 h) of soybean seedling infection. The activity of the two endo-PGs was also investigated during plant infection. PGa and PGb activity reflected very closely the pattern of their transcript accumulation as determined by qRT-PCR. In particular, the PGb encoding gene (Sspgb) was induced at 8 h after inoculation and reached a maximum at 16 h; expression of the PGa encoding gene (Sspga) was comparatively lower, reaching its maximum level later and its rate of increase paralleled that of the S. sclerotiorum b-tubulin gene; the expression of the MDH encoding gene (Ssmdh) was maximal 16 h after infection; soybean pgip transcript began to accumulate 8 h after inoculation reaching a maximum after 24 h. Expression patterns of reported genes are discussed in relation to the ability of S. sclerotiorum to induce disease by regulating endo-PGs and oxalate accumulation to elude the effect of plant PGIP
Characterization and expression of Fusarium graminearum endo-polygalacturonases in vitro and during wheat infection
No full textThis study investigated the expression and characterization of two polygalacturonases (PG1 and PG2) of Fusarium graminearum during infection of wheat spikelets; after purification, these were demonstrated to be products of two unique endo - pg genes annotated in the genome database of F. graminearum . Both genes (Fgpg1 and Fgpg2) were expressed in vitro and during spike infection. PG1 had a greater specific activity, with a maximum at pH 5–7, was largely secreted in liquid culture and clearly detectable in the infected ovary tissue. PG2 was more active at pH 7–7.8, was poorly secreted in liquid culture and faintly detectable in infected ovaries. Both PG-encoding genes were maximally expressed 24 h after wheat spikelet infection, paralleling the expression of a pectin lyase (Fgpnl1) gene; they anticipated the expression of a xylanase gene (FgxylA) that was induced only 48 h after infection with a maximum at 96 h. These data strongly indicate F. graminearum -secreted PG activity at an early stage of wheat infection
Characterization of Fusarium graminearum pectic enzymes secreted in liquid culture and during wheat infection
No full textFusarium graminearum (teleomorph Giberella zeae) causes important diseases in cereals, like wheat, barley and maize. During the infection process this fungus produces mycotoxins and secretes several cell wall degrading enzymes (CWDEs) which could have a role in host colonization. Among CWDEs, we analyzed pectic enzymes produced in liquid culture and during wheat infection. In culture, activity of endo-polygalacturonase (endo-PG) resulted much greater than that of pectin lyase (PNL). Two endo-PGs are secreted and they exhibit different pH range and optimum: one of them, named PG1, has an optimum pH of 5.0 and is inactive at pH 8.0; the second one, named PG2, has an optimum pH of 7.0 and is still active at pH 8.0.
Gene expression analysis performed by real time RT-PCR (qRT-PCR) and enzyme activity data showed that, in liquid culture, PG1 was more expressed than PG2. The expression of pg1 and pg2 genes during the infection of wheat spikes was compared to that of pnl gene, encoding a pectin lyase, and xylA gene, encoding an endo-xylanase. This latter gene was later expressed than pg and pnl genes, but its expression resulted higher. To clarify the importance of F. graminearum endo-PGs in the infection process we performed transformation-mediated gene disruptions. A phenotypic characterization of these mutants will be presented
Wheat transgenic lines overexpressing a bean PGIP showed increased resistance to fungal pathogen
No full textGene disruption approach to investigate the role of Fusarium graminearum and Fusarium verticillioides polygalacturonases during plant infection
No full textFusarium graminearum and Fusarium verticillioides are two important pathogens of cereal species, causing yield and quality losses. These fungi are known to produce polygalacturonase (PG) activity during liquid culture, but the role played by these enzymes during plant infection has not been ascertained yet. In particular, F. graminearum secretes two endo-PG isoforms, encoded by the two putative endo-pg genes contained in its genome, and F. verticillioides secretes an isoform which has been previously characterized together with its encoding gene. In order to establish the role of these PGs in pathogenesis, we have obtained by targeted homologous recombination the transformation-mediated disruption of their pg encoding genes, and the virulence of each knock-out mutant has been therefore evaluated by infecting host plants.
Two different strains of F. graminearum have been transformed: preliminary infection experiments of wheat plants seem to indicate that both pg knock-out mutants maintain the capability to infect wheat, although colonization of spikes appears delayed compared to the wild-type strain. Infection experiments with the F. verticillioides pg knock-out mutant have been performed on maize seedlings and corn husks: the mutant maintains the capability to infect both tissues, but it shows a clearly evident delay in the progression of symptoms.
The demonstration of the importance of F. graminearum and F. verticillioides PGs in pathogenesis might contribute to develop strategies aimed to increase the resistance of host plants to infection by these pathogens
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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