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The xylanase inhibitor TAXI-III limits cell death induced by a xylanase secreted by Fusarium graminearum during wheat infection.
No full textCereals contain xylanase inhibitor proteins (XIs) which inhibit microbial xylanases from glycoside hydrolase families 10 and 11. In wheat, three types of XIs have been identified: Triticum aestivum XI (TAXI), xylanase inhibitor protein (XIP) and thaumatin-like XI (TLXI). These inhibitors are considered part of the defence mechanisms that plants use to counteract microbial pathogens and recently we provided in planta evidences for the protective role of TAXI-III, a member of the TAXI type XIs. To elucidate the molecular mechanism underlying the capacity of the transgenic plants expressing Taxi-III to limit Fusarium Head Blight (FHB) disease symptoms caused by F. graminearum, we performed infiltration experiments on wheat tissues with a xylanase strongly expressed by F. graminearum during wheat spike infection which we have previously demonstrated to induce cell death and hydrogen peroxide accumulation. Experiments performed on glumes of flowering wheat spikes showed that the presence of TAXI-III significantly decreased cell death and hydrogen peroxide accumulation. Most interestingly, similar results were also obtained by infiltrating the same xylanase on glumes of transgenic wheat plants expressing TAXI-III. These results suggest that the reduced FHB symptoms on transgenic TAXI-III plants can be due to the direct inhibition of xylanase activity secreted by the pathogen but also to the capacity of TAXI-III to prevent the recognition of xylanase by a plant receptor possibly involved in cell death elicitation
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
Overexpression of the xylanase inhibitor TAXI-III reduces Fusarium Head Blight symptom in durum wheat.
No full textXylanase inhibitor proteins (XIs) inhibit microbial xylanases from glycoside hydrolase
families 10 and 11. The wheat genome contains three types of XIs: Triticum aestivum XI (TAXI),
xylanase inhibitor protein (XIP) and thaumatin-like XI (TLXI). The genes encoding these inhibitors
may exist in multiple copies in the wheat genome and some of these are localized on chromosome
group 5. XIs are induced by pathogen infection and are responsive to wounding, jasmonic acid and
salicylic acid treatments. They are localized in the apoplastic region and are effective against
xylanases of microbial origin and not against endogenous plant xylanases. On the basis of these
features XIs are considered part of the defence mechanisms that plants use to counteract the activity
of xylanases secreted by microbial pathogens during infection. An additional aspect that reinforces
this possibility is the observation that xylaneses are important components during pathogenesis for
the fungal pathogens Botrytis cinerea and Septoria tritici.
In this report we focus our attention on TAXI-III, one member of the TAXI type XIs that have
been reported to be induced by Fusarium graminearum infection. The expression of the endogenous
Taxi-III is regulated in a tissue-specific manner, being expressed only in developing caryopsis and
roots. In order to facilitate the understanding of its contribution in wheat resistance, we expressed
Taxi-III under control of the constitutive maize Ubiquitin promoter. Results show that TAXI-III
accumulates in all tissues, including those that normally do not contain this inhibitor and its
presence endows the transgenic wheat with new inhibition capacities. We show also that the
transgene-encoded protein is correctly secreted into the apoplast and possesses the expected
inhibition properties against microbial xylanases. In particular, total protein wheat extract or
purified TAXI-III from transgenic plants fully inhibit a purified xylanase from Fusarium
graminearum and to some extent the total xylanase activity produced in vitro by this fungal
pathogen. These new inhibition properties of the transgenic tissues correlate with a significant
reduction of Fusarium Head Blight (FHB) disease symptom caused by F. graminearum.
In conclusion, our results provide for the first time specific evidences at the plant level that
XIs are involved in plant defence against fungal pathogens and show the possibility to manipulate
TAXI-III accumulation to improve wheat resistance against F. graminearum
Durum wheat improvement against fungal pathogens by using protein inhibitors of cell wall degrading enzymes.
No full textBroad-spectrum and durable resistance is one of the most attracting perspective in breeding projects aimed at increasing crop resistance. Since most microbial pathogens need to surmount the plant cell wall to penetrate the host tissue, the reinforcement of this complex compartment should increase the capacity of the host plant to resist the attack of different pathogens.
We pursued this goal by enhancing the host ability to abolish or limit the activity of Cell Wall Degrading Enzymes (CWDEs) secreted by the pathogens during the penetration and colonization of the host tissue. We concentrated our efforts on the containment of the activity of two different CWDEs: the PolyGalacturonases (PGs) and the xylanase inhibitors (XI). PolyGalacturonases (PGs) are among the first CWDEs secreted by fungal pathogens during infection and in some pathosystems they are virulence factors. PGs depolymerize the cell wall pectin, a minor components of the wheat cell wall, and are inhibited by Polygalacturonase Inhibiting proteins (PGIPs). PG activity is also negatively affected by an high degree of pectin methyl esterification. The level of pectin methyl esterification is controlled by the activity of pectin methylesterases (PMEs), which remove the methyl groups, and by its protein inhibitor called Pectin MethylEsterase Inhibitor (PMEI). Thus, indirectly PMEI may negatively affect the activity of PGs by maintaining the pectin with a high degree of methyl esterification. Xylanases are key enzymes in the degradation of arabinoxylans, a main component of the wheat cell wall. These enzymes have been shown to be virulence factors for the fungal pathogens Botrytis cinerea and Mycosphaerella graminicola. The activity of microbial xylanases is controlled in vitro by xylanase inhibitors (XIs) localized in the plant cell wall. However, no evidences in planta for a role of XIs in plant resistance against pathogens have not been reported yet. By using a transgenic approach we showed that PGIP or PMEI can endows durum wheat with new capacities to control the activity of fungal PGs, possibly through a direct interaction or indirectly by modifying the level and pattern of methyl esterification of cell wall pectin. Similarly, transgenic durum wheat plants over-expressing TAXI-III, a member of the TAXI-type XIs, showed new abilities to control fungal xylanases in all tissues, including those that normally do not accumulate this inhibitor. By phytopathogenic tests we demonstrated that these modifications are effective in limiting wheat diseases caused by the fungal pathogens Fusarium graminearum and Bipolaris sorokiniana. We showed also that the reduction of disease symptoms is associated with a reduced accumulation of mycotoxins. In conclusion, these results indicated that the host cell wall polysaccharides, irrespective of their amount and type, plays a key role as functional barrier against different pathogens and that the increased accumulation of glycosidase inhibitors can contribute to maintain their integrity and improve wheat resistance against fungal pathogens
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
Expression of a wheat xylanase inhibitor and of a Fusarium graminearum xylanase in plants increase resistance to pathogens.
No full textDuring host plant infection, pathogens produce many cell wall degrading enzymes (CWDE) in order to colonize the host tissue and also to obtain nutrients. Xylanases are hydrolytic enzymes with a dual role: they catalyze the hydrolysis of xylan, the largest structural polysaccharide of plant cell wall, and some of them can cause necrosis in the host tissue. Since a wheat xylanase inhibitor (TAXI-I) has been shown to inhibit a Botrytis cinerea xylanase, a well known virulence factor of the fungus, we transiently expressed TAXI-I and TAXI-III inhibitors, which has similar inhibitory capability, in tobacco leaves by agroinfiltration. Total leaves protein extracts expressing TAXIs inhibited fungal xylanase activity and TAXIs agroinfiltrated tobacco plants were less susceptible towards B. cinerea by about 20-25%.
Recently we have identified a Fusarium graminearum xylanase (FGSG_03624) shown to cause H2O2 accumulation in wheat tissues and induction of defense genes in Arabidopsis thaliana; we therefore tested its ability to increase resistance against bacterial and fungal pathogens. Exogenous treatment with the xylanase showed a slight reduction of symptoms caused by Pseudomonas syringae pv. maculicola, while the treatment was ineffective against B. cinerea. To further verify this result we also transiently expressed the xylanase in tobacco plants through agroinfiltration; preliminary infection experiments seem to confirm previous results.
Finally we also produced by floral dip transformation Arabidopsis transgenic plants constitutively expressing TAXI-I, TAXI-III and the xylanase FGSG_03624. Infection experiments of these plants with B. cinerea and P. syringae pv. maculicola are in progress
The xylanase inhibitor TAXI-III is involved in wheat resistance against Fusarium graminearum.
No full textCereals contain xylanase inhibitor proteins (XIs) which inhibit microbial xylanases from glycoside hydrolase families 10 and 11. In wheat, three types of XIs have been identified: Triticum aestivum XI (TAXI), xylanase inhibitor protein (XIP) and thaumatin-like XI (TLXI). Each type of XIs is represented by a multiple number of genes. These inhibitors are considered part of the defence mechanisms that plants use to counteract microbial pathogens. Indeed, XIs are induced by pathogen infection and are responsive to mechanical wounding and jasmonic acid and salicylic acid treatments. They are localized in the apoplastic region and are effective against xylanases of microbial origin and not against endogenous plant xylanases. An additional aspect that reinforces the possibility that the XIs are involved in plant defence derives from the observation that xylaneses are important components during pathogenesis for the fungal pathogens Botrytis cinerea and Septoria tritici. Nevertheless, more direct evidences have not been reported yet. Therefore, we produced a number of transgenic plants over-expressing TAXI-III, a member of the TAXI type XIs that is expressed only in developing caryopsis and roots and is induced by pathogen infection, wounding and elicitor treatments. In order to facilitate the understanding of its possible contribution in wheat defence, we designated the transgenic plants to express Taxi-III constitutively. Results showed that TAXI-III accumulated accumulates in all tissues including those that normally do not accumulate it and its presence endows the transgenic wheat with new inhibition capacity. We show also that TAXI-III is correctly secreted into the apoplast and possesses the expected inhibition capacity against microbial xylanases. In particular, total protein wheat extract or purified TAXI-III from transgenic plants inhibits a purified xylanase from Fusarium graminearum and to some extent the total xylanase activity produced in vitro by the fungal pathogens F. graminearum and Bipolaris sorokiniana. The new inhibition properties of the transgenic tissues correlate with a significant reduction of fusarium Fusarium head Head blight Blight (FHB) disease symptom caused by F. graminearum but do not influence significantly leaf spot symptoms caused by B. sorokiniana. Possible differences on the efficacy of TAXI-III to inhibit specific xylanases produced by the two fungal pathogens during host colonization or the presence of additional factors conditioning host colonization at floral or leaf tissues can be responsible for this different outcome.
In conclusion, our results provide for the first time a straight evidence in planta that XIs are involved in plant defence against fungal pathogens and show the possibility to manipulate TAXI-III accumulation to improve wheat resistance against F. graminearum
The wheat xylanase inhibitor TAXI-III interacts with a xylanase secreted by Fusarium graminearum and limits wheat cell death.
No full textCereals contain xylanase inhibitor proteins (XIs) which inhibit microbial xylanases from glycoside hydrolase families 10 and 11. In wheat, three types of XIs have been identified: Triticum aestivum XI (TAXI), xylanase inhibitor protein (XIP) and thaumatin-like XI (TLXI). These inhibitors are considered part of the defence mechanisms that plants use to counteract microbial pathogens: recently, we provided in planta evidences for the protective role of TAXI-III, a member of the TAXI type XIs. To elucidate the molecular mechanism underlying the capacity of the transgenic wheat plants expressing TAXI-III to limit Fusarium Head Blight (FHB) disease symptoms caused by Fusarium graminearum, we performed infiltration experiments on wild-type and transgenic wheat tissues with a xylanase strongly expressed by F. graminearum during wheat spike infection, which we have previously demonstrated to induce cell death and hydrogen peroxide accumulation. Experiments performed on glumes of flowering wild-type wheat spikes showed that the co-infiltration with TAXI-III significantly decreased cell death and hydrogen peroxide accumulation. Most interestingly, similar results were also obtained by infiltrating the same xylanase on glumes of transgenic wheat plants expressing TAXI-III. Molecular modelling studies predict an interaction between the TAXI-III and the active site of the xylanase, thus the formation of this complex might prevent the recognition of the xylanase by a plant receptor possibly involved in cell death elicitation. Therefore these results suggest that the reduced FHB symptoms on transgenic TAXI-III plants can be due to the direct inhibition of xylanase activity secreted by the pathogen but also to the capacity of TAXI-III to block the xylanase necrotizing activity
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