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Abscisic acid negatively interferes with basal defence of barley against Magnaporthe oryzae
Full text linkBackground: Plant hormones are well known regulators which balance plant responses to abiotic and biotic stresses. We investigated the role of abscisic acid (ABA) in resistance of barley (Hordeum vulgare L.) against the plant pathogenic fungus Magnaporthe oryzae.
Results: Exogenous application of ABA prior to inoculation with M. oryzae led to more disease symptoms on barley leaves. This result contrasted the finding that ABA application enhances resistance of barley against the powdery mildew fungus. Microscopic analysis identified diminished penetration resistance as cause for enhanced susceptibility. Consistently, the barley mutant Az34, impaired in ABA biosynthesis, was less susceptible to infection by M. oryzae and displayed elevated penetration resistance as compared to the isogenic wild type cultivar Steptoe. Chemical complementation of Az34 mutant plants by exogenous application of ABA re-established disease severity to the wild type level. The role of ABA in susceptibility of barley against M. oryzae was corroborated by showing that ABA application led to increased disease severity in all barley cultivars under investigation except for the most susceptible cultivar Pallas. Interestingly, endogenous ABA concentrations did not significantly change after infection of barley with M. oryzae.
Conclusion: Our results revealed that elevated ABA levels led to a higher disease severity on barley leaves to M. oryzae. This supports earlier reports on the role of ABA in enhancing susceptibility of rice to the same pathogen and thereby demonstrates a host plant-independent function of this phytohormone in pathogenicity of monocotyledonous plants against M. oryzae
Vergleich der Wirt- und Nichtwirt-Interaktion von Gerste mit verschiedenen Magnaporthe-Arten anhand von histologischen Untersuchungen, Transkriptomstudien und funktionalen Genanalysen
No full textWheat and barley crops are essential for world food security. Both crop species are susceptible to Magnaporthe oryzae, the causal agent of rice blast. However, both plant species are completely and stably resistant against isolates of a Magnaporthe species pathogenic on the grass genus Pennisetum. The mechanisms of this ‘nonhost resistance‘ are not yet fully understood, and the present thesis aimed at identifying genes contributing to its establishment.Thus, microarray analyses of the barley transcriptome during a host interaction (HI) with a M. oryzae isolate and during a nonhost interaction (NHI) with a Pennisetum-associated Magnaporthe isolate were performed. The role of individual candidate genes was investigated in more detail by relating their expression patterns to cellular infection stages observed by microscopy and by the targeted reduction of transcript abundance using a virus-induced gene silencing (VIGS) approach.In both HI and NHI the barley transcriptome responded to Magnaporthe inoculation with an altered, mostly up-regulated, expression of several thousand genes. Among the genes underlying this general transcriptional re-programming 189 candidate genes were identified whose expression was higher during NHI than during HI at aquivalent timepoints, and which could therefore play a role in nonhost resistance. In VIGS experiments the reduced expression of some single candidate genes did not cause a complete break of nonhost resistance, but did affect plant defense reactions in a quantitative manner. The role of the previously identified candidate gene CYP96B22 was analysed in more detail. This gene encodes a putative cytochrome P450 monooxygenase and its expression was induced by 6 h p.i. in NHI. In fact, the pre-penetration growth of both adapted and non-adapted Magnaporthe isolates on the leaf surface already triggered an enhanced transcript accumulation of CYP96B22. This was evidenced, when appressorium formation was reduced or absent, either after fungicide treatment or in a fungal mutant, and CYP96B22 induction still occurred. Therefore, it was concluded that barley and Magnaporthe isolates exchange signals across the intact plant surface before penetration. Microscopy revealed a decrease in effective papillae in the NHI and an increase of invasive pathogen growth in the HI after reduction of CYP96B22 transcript abundance by VIGS. This indicates a crucial function of CYP96B22 in the penetration resistance against Magnaporthe. Since other members of the CYP96 family have been shown to be involved in the biosynthesis of epicuticular waxes, CYP96B22 may contribute to the provision of wax components for structural barriers or to the synthesis of signal molecules.The barley transcriptome analysis was part of the ERA-PG project „TritNONHOST“, in which HI and NHI of barley and wheat with three different pathogens (Magnaporthe, Blumeria and Puccinia) were investigated using a similar experimental setup. Data analyses revealed a large, overlapping gene set underlying the general transcriptional reprogramming in all pathogen interactions. However, nonhost resistance candidate genes identified for Blumeria or Puccinia interactions were different from those identified for the Magnaporthe interaction. These results account for a specific transcriptional nonhost response depending on the pathogen, and are in agreement with results for barley published previously by our group. In a project focusing on the fungal contribution to NHI it was observed that a prior inoculation of barley with Blumeria graminis f.sp. hordei (Bgh) induced susceptibility to the nonhost Magnaporthe isolate. This illustrates that the nonhost isolate, in principal, is able to infect barley. But to do this, it requires the activity of a compatible host pathogen like Bgh which can induce accessibility of plant cells to invasive pathogen growth. Thus, the nonhost isolate may only lack particular pathogenicity factors which play an essential role in the establishment of the HI. For identification of such pathogenicity factors (effector molecules) expressed by the host pathogen M. oryzae, a comparative microarray study of the Magnaporthe transcriptome during HI and NHI was performed. This led to identification of 166 effector candidate genes whose in planta expression was stronger in the host than in the nonhost isolate.In conclusion, the lists of fungal and plant candidate genes documented in the present thesis form a comprehensive basis for further dissection of nonhost resistance mechanisms. This knowledge may be exploited for breeding of new cereal cultivars with improved disease resistance in the future
Vergleich der Wirt- und Nichtwirt-Interaktion von Gerste mit verschiedenen Magnaporthe-Arten anhand von histologischen Untersuchungen, Transkriptomstudien und funktionalen Genanalysen
No full textWheat and barley crops are essential for world food security. Both crop species are susceptible to Magnaporthe oryzae, the causal agent of rice blast. However, both plant species are completely and stably resistant against isolates of a Magnaporthe species pathogenic on the grass genus Pennisetum. The mechanisms of this ‘nonhost resistance‘ are not yet fully understood, and the present thesis aimed at identifying genes contributing to its establishment.Thus, microarray analyses of the barley transcriptome during a host interaction (HI) with a M. oryzae isolate and during a nonhost interaction (NHI) with a Pennisetum-associated Magnaporthe isolate were performed. The role of individual candidate genes was investigated in more detail by relating their expression patterns to cellular infection stages observed by microscopy and by the targeted reduction of transcript abundance using a virus-induced gene silencing (VIGS) approach.In both HI and NHI the barley transcriptome responded to Magnaporthe inoculation with an altered, mostly up-regulated, expression of several thousand genes. Among the genes underlying this general transcriptional re-programming 189 candidate genes were identified whose expression was higher during NHI than during HI at aquivalent timepoints, and which could therefore play a role in nonhost resistance. In VIGS experiments the reduced expression of some single candidate genes did not cause a complete break of nonhost resistance, but did affect plant defense reactions in a quantitative manner. The role of the previously identified candidate gene CYP96B22 was analysed in more detail. This gene encodes a putative cytochrome P450 monooxygenase and its expression was induced by 6 h p.i. in NHI. In fact, the pre-penetration growth of both adapted and non-adapted Magnaporthe isolates on the leaf surface already triggered an enhanced transcript accumulation of CYP96B22. This was evidenced, when appressorium formation was reduced or absent, either after fungicide treatment or in a fungal mutant, and CYP96B22 induction still occurred. Therefore, it was concluded that barley and Magnaporthe isolates exchange signals across the intact plant surface before penetration. Microscopy revealed a decrease in effective papillae in the NHI and an increase of invasive pathogen growth in the HI after reduction of CYP96B22 transcript abundance by VIGS. This indicates a crucial function of CYP96B22 in the penetration resistance against Magnaporthe. Since other members of the CYP96 family have been shown to be involved in the biosynthesis of epicuticular waxes, CYP96B22 may contribute to the provision of wax components for structural barriers or to the synthesis of signal molecules.The barley transcriptome analysis was part of the ERA-PG project „TritNONHOST“, in which HI and NHI of barley and wheat with three different pathogens (Magnaporthe, Blumeria and Puccinia) were investigated using a similar experimental setup. Data analyses revealed a large, overlapping gene set underlying the general transcriptional reprogramming in all pathogen interactions. However, nonhost resistance candidate genes identified for Blumeria or Puccinia interactions were different from those identified for the Magnaporthe interaction. These results account for a specific transcriptional nonhost response depending on the pathogen, and are in agreement with results for barley published previously by our group. In a project focusing on the fungal contribution to NHI it was observed that a prior inoculation of barley with Blumeria graminis f.sp. hordei (Bgh) induced susceptibility to the nonhost Magnaporthe isolate. This illustrates that the nonhost isolate, in principal, is able to infect barley. But to do this, it requires the activity of a compatible host pathogen like Bgh which can induce accessibility of plant cells to invasive pathogen growth. Thus, the nonhost isolate may only lack particular pathogenicity factors which play an essential role in the establishment of the HI. For identification of such pathogenicity factors (effector molecules) expressed by the host pathogen M. oryzae, a comparative microarray study of the Magnaporthe transcriptome during HI and NHI was performed. This led to identification of 166 effector candidate genes whose in planta expression was stronger in the host than in the nonhost isolate.In conclusion, the lists of fungal and plant candidate genes documented in the present thesis form a comprehensive basis for further dissection of nonhost resistance mechanisms. This knowledge may be exploited for breeding of new cereal cultivars with improved disease resistance in the future
A comparative analysis of nonhost resistance across the two Triticeae crop species wheat and barley
No full textBackground: Nonhost resistance (NHR) protects plants against a vast number of non-adapted pathogens which implicates a potential exploitation as source for novel disease resistance strategies. Aiming at a fundamental understanding of NHR a global analysis of transcriptome reprogramming in the economically important Triticeae cereals wheat and barley, comparing host and nonhost interactions in three major fungal pathosystems responsible for powdery mildew (Blumeria graminis ff. ssp.), cereal blast (Magnaporthe sp.) and leaf rust (Puccinia sp.) diseases, was performed.
Results: In each pathosystem a significant transcriptome reprogramming by adapted- or non-adapted pathogen isolates was observed, with considerable overlap between Blumeria, Magnaporthe and Puccinia. Small subsets of these general pathogen-regulated genes were identified as differentially regulated between host and corresponding nonhost interactions, indicating a fine-tuning of the general pathogen response during the course of co-evolution. Additionally, the host- or nonhost-related responses were rather specific for each pair of adapted and non-adapted isolates, indicating that the nonhost resistance-related responses were to a great extent pathosystem-specific. This pathosystem-specific reprogramming may reflect different resistance mechanisms operating against non-adapted pathogens with different lifestyles, or equally, different co-option of the hosts by the adapted isolates to create an optimal environment for infection. To compare the transcriptional reprogramming between wheat and barley, putative orthologues were identified. Within the wheat and barley general pathogen-regulated genes, temporal expression profiles of orthologues looked similar, indicating conserved general responses in Triticeae against fungal attack. However, the comparison of orthologues differentially expressed between host and nonhost interactions revealed fewer commonalities between wheat and barley, but rather suggested different host or nonhost responses in the two cereal species.
Conclusions: Taken together, our results suggest independent co-evolutionary forces acting on host pathosystems mirrored by barley- or wheat-specific nonhost responses. As a result of evolutionary processes, at least for the pathosystems investigated, NHR appears to rely on rather specific plant response
Transcription profiling by array of wheat after inoculation with Puccinia triticina, Puccinia hordei or mock-inoculation to identify candidate genes for nonhost resistance against rust disease
No full textIn this experiment the transcriptome reprogramming in wheat during host and nonhost interaction with Puccinia sp. was analyzed in a time-series approach. Ten days old wheat plants of cv. Renan were mock-inoculated or inoculated with P. triticina (Pt), BRW96258 isolate, or P. hordei (Ph), 1.2.1 isolate. After 12, 24, 36 and 48 hours first leaves were sampled. Total RNA was extracted using the RNeasy Plant Mini Kit (Qiagen, Hilden, Germany), the Ambion TURBO DNA-free DNase Kit was used for DNA elimination, and RNA was hybridized to Agilent 44k oligonucleotide arrays
Transcription profiling by array of barley after inoculation with Puccinia hordei, Puccinia triticina or mock-inoculation to identify candidate genes for nonhost resistance against rust disease
No full textIn this experiment the transcriptome reprogramming in barley during host and nonhost interaction with Puccinia sp. was analyzed in a time-series approach. Ten days old barley plants of cv. Vada were mock-inoculated or inoculated with P. hordei (Ph), 1.2.1 isolate, or P. triticina (Pt), BRW96258 isolate. After 12, 24, 36 and 48 hours first leaves were sampled. Total RNA was extracted using the RNeasy Plant Mini Kit (Qiagen, Hilden, Germany), the Ambion TURBO DNA-free DNase Kit was used for DNA elimination, and RNA was hybridized to Agilent 44k oligonucleotide arrays
Transcription profiling by array of wheat after inoculation with Puccinia triticina, Puccinia hordei or mock-inoculation to identify candidate genes for nonhost resistance against rust disease
No full textIn this experiment the transcriptome reprogramming in wheat during host and nonhost interaction with Puccinia sp. was analyzed in a time-series approach. Ten days old wheat plants of cv. Renan were mock-inoculated or inoculated with P. triticina (Pt), BRW96258 isolate, or P. hordei (Ph), 1.2.1 isolate. After 12, 24, 36 and 48 hours first leaves were sampled. Total RNA was extracted using the RNeasy Plant Mini Kit (Qiagen, Hilden, Germany), the Ambion TURBO DNA-free DNase Kit was used for DNA elimination, and RNA was hybridized to Agilent 44k oligonucleotide arrays
Transcription profiling by array of barley after inoculation with Puccinia hordei, Puccinia triticina or mock-inoculation to identify candidate genes for nonhost resistance against rust disease
No full textIn this experiment the transcriptome reprogramming in barley during host and nonhost interaction with Puccinia sp. was analyzed in a time-series approach. Ten days old barley plants of cv. Vada were mock-inoculated or inoculated with P. hordei (Ph), 1.2.1 isolate, or P. triticina (Pt), BRW96258 isolate. After 12, 24, 36 and 48 hours first leaves were sampled. Total RNA was extracted using the RNeasy Plant Mini Kit (Qiagen, Hilden, Germany), the Ambion TURBO DNA-free DNase Kit was used for DNA elimination, and RNA was hybridized to Agilent 44k oligonucleotide arrays
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
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