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Katharina Pawlowski - One of the best experts on this subject based on the ideXlab platform.
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accumulation of and response to auxins in roots and nodules of the Actinorhizal Plant datisca glomerata compared to the model legume medicago truncatula
Frontiers in Plant Science, 2019Co-Authors: Irina V. Demina, Pooja Jha Maity, Anurupa Nagchowdhury, Kirill N Demchenko, Eric Van Der Graaff, Thomas Roitsch, Ulrike Mathesius, Katharina PawlowskiAbstract:Actinorhizal nodules are structurally different from legume nodules and show a greater similarity to lateral roots. Because of the important role of auxins in lateral root and nodule formation, auxin profiles were examined in roots and nodules of the Actinorhizal species Datisca glomerata and the model legume Medicago truncatula. The auxin response in roots and nodules of both species was analyzed in transgenic root systems expressing a beta-glucuronidase gene under control of the synthetic auxin-responsive promoter DR5. The effects of two different auxin on root development were compared for both species. The auxin present in nodules at the highest levels was phenylacetic acid (PAA). No differences were found between the concentrations of active auxins of roots vs. nodules, while levels of the auxin conjugate indole-3-acetic acid-alanine were increased in nodules compared to roots of both species. Because auxins typically act in concert with cytokinins, cytokinins were also quantified. Concentrations of cis-zeatin and some glycosylated cytokinins were dramatically increased in nodules compared to roots of D. glomerata, but not of M. truncatula. The ratio of active auxins to cytokinins remained similar in nodules compared to roots in both species. The auxin response, as shown by the activation of the DR5 promoter, seemed significantly reduced in nodules compared to roots of both species, suggesting the accumulation of auxins in cell types that do not express the signal transduction pathway leading to DR5 activation. Effects on root development were analyzed for the synthetic auxin naphthaleneacetic acid (NAA) and PAA, the dominant auxin in nodules. Both auxins had similar effects, except that the sensitivity of roots to PAA was lower than to NAA. However, while the effects of both auxins on primary root growth were similar for both species, effects on root branching were different: both auxins had the classical positive effect on root branching in M. truncatula, but a negative effect in D. glomerata. Such a negative effect of exogenous auxin on root branching has previously been found for a cucurbit that forms lateral root primordia in the meristem of the parental root; however, root branching in D. glomerata does not follow that pattern.
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the impact of salinity on the symbiosis between casuarina glauca sieb ex spreng and n2 fixing frankia bacteria based on the analysis of nitrogen and carbon metabolism
Plant and Soil, 2016Co-Authors: Nuno Duro, Paula Batistasantos, Mario Costa, Rodrigo Maia, Isabel Videira E Castro, Margarida Ramos, Jose C Ramalho, Katharina PawlowskiAbstract:Background and aims Casuarina glauca is an Actinorhizal Plant that establishes root-nodule symbiosis with N2-fixing bacteria of the genus Frankia. This Plant is highly recalcitrant to extreme environmental conditions such as salinity and drought. The aim of this study was to evaluate the impact of salt stress on the symbiotic relationship between C. glauca and Frankia Thr, focusing on N and C metabolism.
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comparison of the nodule vs root transcriptome of the Actinorhizal Plant datisca glomerata Actinorhizal nodules contain a specific class of defensins
PLOS ONE, 2013Co-Authors: Irina V. Demina, Patricia Santos, Malgorzata Plaszczyca, Tomas Persson, Katharina PawlowskiAbstract:Actinorhizal root nodule symbioses are very diverse, and the symbiosis of Datisca glomerata has previously been shown to have many unusual aspects. In order to gain molecular information on the infection mechanism, nodule development and nodule metabolism, we compared the transcriptomes of D. glomerata roots and nodules. Root and nodule libraries representing the 3′-ends of cDNAs were subjected to high-throughput parallel 454 sequencing. To identify the corresponding genes and to improve the assembly, Illumina sequencing of the nodule transcriptome was performed as well. The evaluation revealed 406 differentially regulated genes, 295 of which (72.7%) could be assigned a function based on homology. Analysis of the nodule transcriptome showed that genes encoding components of the common symbiosis signaling pathway were present in nodules of D. glomerata, which in combination with the previously established function of SymRK in D. glomerata nodulation suggests that this pathway is also active in Actinorhizal Cucurbitales. Furthermore, comparison of the D. glomerata nodule transcriptome with nodule transcriptomes from Actinorhizal Fagales revealed a new subgroup of nodule-specific defensins that might play a role specific to Actinorhizal symbioses. The D. glomerata members of this defensin subgroup contain an acidic C-terminal domain that was never found in Plant defensins before.
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Auxins and cytokinins in roots, hairy roots and nodules of the Actinorhizal Plant Datisca glomerata and the model legume Medicago truncatula
2013Co-Authors: Irina V. Demina, Eric Van Der Graaff, Thomas Roitsch, Ulrike Mathesius, Katharina PawlowskiAbstract:Auxins and cytokinins in roots, hairy roots and nodules of the Actinorhizal Plant Datisca glomerata and the model legume Medicago truncatula
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cysteine rich peptide genes are expressed in the infected nodule cells of the Actinorhizal Plant datisca glomerata
2013Co-Authors: Irina V. Demina, Katharina PawlowskiAbstract:The Actinorhizal symbiosis is entered by nitrogen-fixing actinobacteria of the genus Frankia and a large group of woody Plant species distributed among eight dicot families. The Actinorhizal symbiosis, as well as the legume-rhizobia symbiosis, involves the stable intracellular accommodation of the microsymbionts in special organs called root nodules. Within the nodules, the nitrogen-fixing bacteria are provided with carbon sources by the host Plant while supplying the Plant with fixed nitrogen, which is often a limiting factor in Plant growth and development.Datisca glomerata (C. Presl.) Baill. (Datiscaceae, Cucurbitales) is a suffruticose Plant with a relatively short generation time of six months, and therefore represents the Actinorhizal species most suited as a genetic model system. In order to obtain an overview of nodule development and metabolism, the nodule transcriptome was analyzed. Comparison of nodule vs. root transcriptomes allowed identification of potential marker genes for nodule development. The activity of the promoters of two of these genes was studied in Planta. Furthermore, auxins and cytokinins were quantified in roots and nodules, and the auxin responses in roots were compared in D. glomerata and the model legume Medicago truncatula.Our results indicate that in Actinorhizal Plants signaling in the root epidermis leading to nodule organogenesis follows the common symbiosis pathway described for the legume-rhizobia symbiosis and arbuscular mycorrhiza. Moreover, we discovered a group of nodule-specific genes encoding defensin-like peptides with an unusual C-terminal domain that had not been found in other Plant species. A possible role in the symbiosis-specific differentiation of the microsymbiont and in nodule development was suggested for these cysteine-rich peptides. Finally, we showed that D. glomerata and M. truncatula differ in their auxin and cytokinin requirements for the development of both nodules and lateral roots.
Elodie Pirolles - One of the best experts on this subject based on the ideXlab platform.
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Chitotetraose activates the fungal-dependent endosymbiotic signaling pathway in Actinorhizal Plant species
PLoS ONE, 2019Co-Authors: Mireille Chabaud, Claudine Franche, Leandro Imanishi, Joëlle Fournier, Lukas Brichet, Iltaf Abdou-pavy, Laurent Brottier, Elodie Pirolles, Valérie Hocher, Didier BoguszAbstract:Mutualistic Plant-microbe associations are widespread in natural ecosystems and have made major contributions throughout the evolutionary history of terrestrial Plants. Amongst the most remarkable of these are the so-called root endosymbioses, resulting from the intra-cellular colonization of host tissues by either arbuscular mycorrhizal (AM) fungi or nitrogen-fixing bacteria that both provide key nutrients to the host in exchange for energy-rich photo-synthates. Actinorhizal host Plants, members of the Eurosid 1 clade, are able to associate with both AM fungi and nitrogen-fixing actinomycetes known as Frankia. Currently, little is known about the molecular signaling that allows these Plants to recognize their fungal and bacterial partners. In this article, we describe the use of an in vivo Ca 2+ reporter to identify symbiotic signaling responses to AM fungi in roots of both Casuarina glauca and Discaria tri-nervis, Actinorhizal species with contrasting modes of Frankia colonization. This approach has revealed that, for both Actinorhizal hosts, the short-chain chitin oligomer chitotetraose is able to mimic AM fungal exudates in activating the conserved symbiosis signaling pathway (CSSP) in epidermal root cells targeted by AM fungi. These results mirror findings in other AM host Plants including legumes and the monocot rice. In addition, we show that chitote-traose is a more efficient elicitor of CSSP activation compared to AM fungal lipo-chitooligo-saccharides. These findings reinforce the likely role of short-chain chitin oligomers during the initial stages of the AM association, and are discussed in relation to both our current knowledge about molecular signaling during Frankia recognition as well as the different microsymbiont root colonization mechanisms employed by Actinorhizal hosts. PLOS ONE | https://doi.org/10.1371/journal.pone.
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Cell remodeling and subtilase gene expression in the Actinorhizal Plant Discaria trinervis highlight host orchestration of intercellular Frankia colonization
New Phytologist, 2018Co-Authors: Joëlle Fournier, Leandro Imanishi, Alice Vayssieres, Mireille Chabaud, Lukas Brichet, Iltaf Abdou-pavy, Andrea Genre, Hernán Ramiro Lascano, Nacira Muñoz, Elodie PirollesAbstract:Nitrogen-fixing filamentous Frankia colonize the root tissues of its Actinorhizal host Discaria trinervis via an exclusively intercellular pathway. Here we present studies aimed at uncovering mechanisms associated with this little-researched mode of root entry, and in particular the extent to which the host Plant is an active partner during this process. Detailed characterization of the expression patterns of infection-associated Actinorhizal host genes has provided valuable tools to identify intercellular infection sites, thus allowing in vivo confocal microscopic studies of the early stages of Frankia colonization. The subtilisin-like serine protease gene Dt12, as well as its Casuarina glauca homolog Cg12, are specifically expressed at sites of Frankia intercellular colonization of D. trinervis outer root tissues. This is accompanied by nucleo-cytoplasmic reorganization in the adjacent host cells and major remodeling of the intercellular apoplastic compartment. These findings lead us to propose that the Actinorhizal host plays a major role in modifying both the size and composition of the intercellular apoplast in order to accommodate the filamentous microsymbiont. The implications of these findings are discussed in the light of the analogies that can be made with the orchestrating role of host legumes during intracellular root hair colonization by nitrogen-fixing rhizobia.
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chitinase resistant hydrophilic symbiotic factors secreted by frankia activate both ca2 spiking and nin gene expression in the Actinorhizal Plant casuarina glauca
New Phytologist, 2016Co-Authors: Mireille Chabaud, Claudine Franche, Didier Bogusz, Joëlle Fournier, Elodie Pirolles, Hassen Gherbi, Virginie Vaissayre, Daniel Moukouanga, Louis S Tisa, David G BarkerAbstract:Although it is now well-established that decorated lipo-chitooligosaccharide Nod factors are the key rhizobial signals which initiate infection/nodulation in host legume species, the identity of the equivalent microbial signaling molecules in the Frankia/Actinorhizal association remains elusive. With the objective of identifying Frankia symbiotic factors we present a novel approach based on both molecular and cellular pre-infection reporters expressed in the model Actinorhizal species Casuarina glauca. By introducing the nuclear-localized cameleon Nup-YC2.1 into Casuarina glauca we show that cell-free culture supernatants of the compatible Frankia CcI3 strain are able to elicit sustained high frequency Ca(2+) spiking in host root hairs. Furthermore, an excellent correlation exists between the triggering of nuclear Ca(2+) spiking and the transcriptional activation of the ProCgNIN:GFP reporter as a function of the Frankia strain tested. These two pre-infection symbiotic responses have been used in combination to show that the signal molecules present in the Frankia CcI3 supernatant are hydrophilic, of low molecular weight and resistant to chitinase degradation. In conclusion, the biologically active symbiotic signals secreted by Frankia appear to be chemically distinct from the currently known chitin-based rhizobial/arbuscular mycorrhizal signaling molecules. Convenient bioassays in Casuarina glauca are now available for their full characterization.
Irina V. Demina - One of the best experts on this subject based on the ideXlab platform.
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accumulation of and response to auxins in roots and nodules of the Actinorhizal Plant datisca glomerata compared to the model legume medicago truncatula
Frontiers in Plant Science, 2019Co-Authors: Irina V. Demina, Pooja Jha Maity, Anurupa Nagchowdhury, Kirill N Demchenko, Eric Van Der Graaff, Thomas Roitsch, Ulrike Mathesius, Katharina PawlowskiAbstract:Actinorhizal nodules are structurally different from legume nodules and show a greater similarity to lateral roots. Because of the important role of auxins in lateral root and nodule formation, auxin profiles were examined in roots and nodules of the Actinorhizal species Datisca glomerata and the model legume Medicago truncatula. The auxin response in roots and nodules of both species was analyzed in transgenic root systems expressing a beta-glucuronidase gene under control of the synthetic auxin-responsive promoter DR5. The effects of two different auxin on root development were compared for both species. The auxin present in nodules at the highest levels was phenylacetic acid (PAA). No differences were found between the concentrations of active auxins of roots vs. nodules, while levels of the auxin conjugate indole-3-acetic acid-alanine were increased in nodules compared to roots of both species. Because auxins typically act in concert with cytokinins, cytokinins were also quantified. Concentrations of cis-zeatin and some glycosylated cytokinins were dramatically increased in nodules compared to roots of D. glomerata, but not of M. truncatula. The ratio of active auxins to cytokinins remained similar in nodules compared to roots in both species. The auxin response, as shown by the activation of the DR5 promoter, seemed significantly reduced in nodules compared to roots of both species, suggesting the accumulation of auxins in cell types that do not express the signal transduction pathway leading to DR5 activation. Effects on root development were analyzed for the synthetic auxin naphthaleneacetic acid (NAA) and PAA, the dominant auxin in nodules. Both auxins had similar effects, except that the sensitivity of roots to PAA was lower than to NAA. However, while the effects of both auxins on primary root growth were similar for both species, effects on root branching were different: both auxins had the classical positive effect on root branching in M. truncatula, but a negative effect in D. glomerata. Such a negative effect of exogenous auxin on root branching has previously been found for a cucurbit that forms lateral root primordia in the meristem of the parental root; however, root branching in D. glomerata does not follow that pattern.
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comparison of the nodule vs root transcriptome of the Actinorhizal Plant datisca glomerata Actinorhizal nodules contain a specific class of defensins
PLOS ONE, 2013Co-Authors: Irina V. Demina, Patricia Santos, Malgorzata Plaszczyca, Tomas Persson, Katharina PawlowskiAbstract:Actinorhizal root nodule symbioses are very diverse, and the symbiosis of Datisca glomerata has previously been shown to have many unusual aspects. In order to gain molecular information on the infection mechanism, nodule development and nodule metabolism, we compared the transcriptomes of D. glomerata roots and nodules. Root and nodule libraries representing the 3′-ends of cDNAs were subjected to high-throughput parallel 454 sequencing. To identify the corresponding genes and to improve the assembly, Illumina sequencing of the nodule transcriptome was performed as well. The evaluation revealed 406 differentially regulated genes, 295 of which (72.7%) could be assigned a function based on homology. Analysis of the nodule transcriptome showed that genes encoding components of the common symbiosis signaling pathway were present in nodules of D. glomerata, which in combination with the previously established function of SymRK in D. glomerata nodulation suggests that this pathway is also active in Actinorhizal Cucurbitales. Furthermore, comparison of the D. glomerata nodule transcriptome with nodule transcriptomes from Actinorhizal Fagales revealed a new subgroup of nodule-specific defensins that might play a role specific to Actinorhizal symbioses. The D. glomerata members of this defensin subgroup contain an acidic C-terminal domain that was never found in Plant defensins before.
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Auxins and cytokinins in roots, hairy roots and nodules of the Actinorhizal Plant Datisca glomerata and the model legume Medicago truncatula
2013Co-Authors: Irina V. Demina, Eric Van Der Graaff, Thomas Roitsch, Ulrike Mathesius, Katharina PawlowskiAbstract:Auxins and cytokinins in roots, hairy roots and nodules of the Actinorhizal Plant Datisca glomerata and the model legume Medicago truncatula
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cysteine rich peptide genes are expressed in the infected nodule cells of the Actinorhizal Plant datisca glomerata
2013Co-Authors: Irina V. Demina, Katharina PawlowskiAbstract:The Actinorhizal symbiosis is entered by nitrogen-fixing actinobacteria of the genus Frankia and a large group of woody Plant species distributed among eight dicot families. The Actinorhizal symbiosis, as well as the legume-rhizobia symbiosis, involves the stable intracellular accommodation of the microsymbionts in special organs called root nodules. Within the nodules, the nitrogen-fixing bacteria are provided with carbon sources by the host Plant while supplying the Plant with fixed nitrogen, which is often a limiting factor in Plant growth and development.Datisca glomerata (C. Presl.) Baill. (Datiscaceae, Cucurbitales) is a suffruticose Plant with a relatively short generation time of six months, and therefore represents the Actinorhizal species most suited as a genetic model system. In order to obtain an overview of nodule development and metabolism, the nodule transcriptome was analyzed. Comparison of nodule vs. root transcriptomes allowed identification of potential marker genes for nodule development. The activity of the promoters of two of these genes was studied in Planta. Furthermore, auxins and cytokinins were quantified in roots and nodules, and the auxin responses in roots were compared in D. glomerata and the model legume Medicago truncatula.Our results indicate that in Actinorhizal Plants signaling in the root epidermis leading to nodule organogenesis follows the common symbiosis pathway described for the legume-rhizobia symbiosis and arbuscular mycorrhiza. Moreover, we discovered a group of nodule-specific genes encoding defensin-like peptides with an unusual C-terminal domain that had not been found in other Plant species. A possible role in the symbiosis-specific differentiation of the microsymbiont and in nodule development was suggested for these cysteine-rich peptides. Finally, we showed that D. glomerata and M. truncatula differ in their auxin and cytokinin requirements for the development of both nodules and lateral roots.
Joëlle Fournier - One of the best experts on this subject based on the ideXlab platform.
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Chitotetraose activates the fungal-dependent endosymbiotic signaling pathway in Actinorhizal Plant species
PLoS ONE, 2019Co-Authors: Mireille Chabaud, Claudine Franche, Leandro Imanishi, Joëlle Fournier, Lukas Brichet, Iltaf Abdou-pavy, Laurent Brottier, Elodie Pirolles, Valérie Hocher, Didier BoguszAbstract:Mutualistic Plant-microbe associations are widespread in natural ecosystems and have made major contributions throughout the evolutionary history of terrestrial Plants. Amongst the most remarkable of these are the so-called root endosymbioses, resulting from the intra-cellular colonization of host tissues by either arbuscular mycorrhizal (AM) fungi or nitrogen-fixing bacteria that both provide key nutrients to the host in exchange for energy-rich photo-synthates. Actinorhizal host Plants, members of the Eurosid 1 clade, are able to associate with both AM fungi and nitrogen-fixing actinomycetes known as Frankia. Currently, little is known about the molecular signaling that allows these Plants to recognize their fungal and bacterial partners. In this article, we describe the use of an in vivo Ca 2+ reporter to identify symbiotic signaling responses to AM fungi in roots of both Casuarina glauca and Discaria tri-nervis, Actinorhizal species with contrasting modes of Frankia colonization. This approach has revealed that, for both Actinorhizal hosts, the short-chain chitin oligomer chitotetraose is able to mimic AM fungal exudates in activating the conserved symbiosis signaling pathway (CSSP) in epidermal root cells targeted by AM fungi. These results mirror findings in other AM host Plants including legumes and the monocot rice. In addition, we show that chitote-traose is a more efficient elicitor of CSSP activation compared to AM fungal lipo-chitooligo-saccharides. These findings reinforce the likely role of short-chain chitin oligomers during the initial stages of the AM association, and are discussed in relation to both our current knowledge about molecular signaling during Frankia recognition as well as the different microsymbiont root colonization mechanisms employed by Actinorhizal hosts. PLOS ONE | https://doi.org/10.1371/journal.pone.
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Cell remodeling and subtilase gene expression in the Actinorhizal Plant Discaria trinervis highlight host orchestration of intercellular Frankia colonization
New Phytologist, 2018Co-Authors: Joëlle Fournier, Leandro Imanishi, Alice Vayssieres, Mireille Chabaud, Lukas Brichet, Iltaf Abdou-pavy, Andrea Genre, Hernán Ramiro Lascano, Nacira Muñoz, Elodie PirollesAbstract:Nitrogen-fixing filamentous Frankia colonize the root tissues of its Actinorhizal host Discaria trinervis via an exclusively intercellular pathway. Here we present studies aimed at uncovering mechanisms associated with this little-researched mode of root entry, and in particular the extent to which the host Plant is an active partner during this process. Detailed characterization of the expression patterns of infection-associated Actinorhizal host genes has provided valuable tools to identify intercellular infection sites, thus allowing in vivo confocal microscopic studies of the early stages of Frankia colonization. The subtilisin-like serine protease gene Dt12, as well as its Casuarina glauca homolog Cg12, are specifically expressed at sites of Frankia intercellular colonization of D. trinervis outer root tissues. This is accompanied by nucleo-cytoplasmic reorganization in the adjacent host cells and major remodeling of the intercellular apoplastic compartment. These findings lead us to propose that the Actinorhizal host plays a major role in modifying both the size and composition of the intercellular apoplast in order to accommodate the filamentous microsymbiont. The implications of these findings are discussed in the light of the analogies that can be made with the orchestrating role of host legumes during intracellular root hair colonization by nitrogen-fixing rhizobia.
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chitinase resistant hydrophilic symbiotic factors secreted by frankia activate both ca2 spiking and nin gene expression in the Actinorhizal Plant casuarina glauca
New Phytologist, 2016Co-Authors: Mireille Chabaud, Claudine Franche, Didier Bogusz, Joëlle Fournier, Elodie Pirolles, Hassen Gherbi, Virginie Vaissayre, Daniel Moukouanga, Louis S Tisa, David G BarkerAbstract:Although it is now well-established that decorated lipo-chitooligosaccharide Nod factors are the key rhizobial signals which initiate infection/nodulation in host legume species, the identity of the equivalent microbial signaling molecules in the Frankia/Actinorhizal association remains elusive. With the objective of identifying Frankia symbiotic factors we present a novel approach based on both molecular and cellular pre-infection reporters expressed in the model Actinorhizal species Casuarina glauca. By introducing the nuclear-localized cameleon Nup-YC2.1 into Casuarina glauca we show that cell-free culture supernatants of the compatible Frankia CcI3 strain are able to elicit sustained high frequency Ca(2+) spiking in host root hairs. Furthermore, an excellent correlation exists between the triggering of nuclear Ca(2+) spiking and the transcriptional activation of the ProCgNIN:GFP reporter as a function of the Frankia strain tested. These two pre-infection symbiotic responses have been used in combination to show that the signal molecules present in the Frankia CcI3 supernatant are hydrophilic, of low molecular weight and resistant to chitinase degradation. In conclusion, the biologically active symbiotic signals secreted by Frankia appear to be chemically distinct from the currently known chitin-based rhizobial/arbuscular mycorrhizal signaling molecules. Convenient bioassays in Casuarina glauca are now available for their full characterization.
Leandro Imanishi - One of the best experts on this subject based on the ideXlab platform.
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Chitotetraose activates the fungal-dependent endosymbiotic signaling pathway in Actinorhizal Plant species
PLoS ONE, 2019Co-Authors: Mireille Chabaud, Claudine Franche, Leandro Imanishi, Joëlle Fournier, Lukas Brichet, Iltaf Abdou-pavy, Laurent Brottier, Elodie Pirolles, Valérie Hocher, Didier BoguszAbstract:Mutualistic Plant-microbe associations are widespread in natural ecosystems and have made major contributions throughout the evolutionary history of terrestrial Plants. Amongst the most remarkable of these are the so-called root endosymbioses, resulting from the intra-cellular colonization of host tissues by either arbuscular mycorrhizal (AM) fungi or nitrogen-fixing bacteria that both provide key nutrients to the host in exchange for energy-rich photo-synthates. Actinorhizal host Plants, members of the Eurosid 1 clade, are able to associate with both AM fungi and nitrogen-fixing actinomycetes known as Frankia. Currently, little is known about the molecular signaling that allows these Plants to recognize their fungal and bacterial partners. In this article, we describe the use of an in vivo Ca 2+ reporter to identify symbiotic signaling responses to AM fungi in roots of both Casuarina glauca and Discaria tri-nervis, Actinorhizal species with contrasting modes of Frankia colonization. This approach has revealed that, for both Actinorhizal hosts, the short-chain chitin oligomer chitotetraose is able to mimic AM fungal exudates in activating the conserved symbiosis signaling pathway (CSSP) in epidermal root cells targeted by AM fungi. These results mirror findings in other AM host Plants including legumes and the monocot rice. In addition, we show that chitote-traose is a more efficient elicitor of CSSP activation compared to AM fungal lipo-chitooligo-saccharides. These findings reinforce the likely role of short-chain chitin oligomers during the initial stages of the AM association, and are discussed in relation to both our current knowledge about molecular signaling during Frankia recognition as well as the different microsymbiont root colonization mechanisms employed by Actinorhizal hosts. PLOS ONE | https://doi.org/10.1371/journal.pone.
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Cell remodeling and subtilase gene expression in the Actinorhizal Plant Discaria trinervis highlight host orchestration of intercellular Frankia colonization
New Phytologist, 2018Co-Authors: Joëlle Fournier, Leandro Imanishi, Alice Vayssieres, Mireille Chabaud, Lukas Brichet, Iltaf Abdou-pavy, Andrea Genre, Hernán Ramiro Lascano, Nacira Muñoz, Elodie PirollesAbstract:Nitrogen-fixing filamentous Frankia colonize the root tissues of its Actinorhizal host Discaria trinervis via an exclusively intercellular pathway. Here we present studies aimed at uncovering mechanisms associated with this little-researched mode of root entry, and in particular the extent to which the host Plant is an active partner during this process. Detailed characterization of the expression patterns of infection-associated Actinorhizal host genes has provided valuable tools to identify intercellular infection sites, thus allowing in vivo confocal microscopic studies of the early stages of Frankia colonization. The subtilisin-like serine protease gene Dt12, as well as its Casuarina glauca homolog Cg12, are specifically expressed at sites of Frankia intercellular colonization of D. trinervis outer root tissues. This is accompanied by nucleo-cytoplasmic reorganization in the adjacent host cells and major remodeling of the intercellular apoplastic compartment. These findings lead us to propose that the Actinorhizal host plays a major role in modifying both the size and composition of the intercellular apoplast in order to accommodate the filamentous microsymbiont. The implications of these findings are discussed in the light of the analogies that can be made with the orchestrating role of host legumes during intracellular root hair colonization by nitrogen-fixing rhizobia.
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Role of auxin during intercellular infection of Discaria trinervis by Frankia
Frontiers in Plant Science, 2014Co-Authors: Leandro Imanishi, Laurent Laplaze, Francine Manuelle Perrine-walker, Adama Ndour, Alice Vayssieres, Geneviève Conejero, Mikael Lucas, Antony Champion, Luis Wall, Sergio SvistoonoffAbstract:ogen-fixing nodules induced by Frankia in the Actinorhizal Plant Discaria trinervis result from a primitive intercellular root invasion pathway that does not involve root hair deformation and infection threads. Here, we analyzed the role of auxin in this intercellular infection pathway at the molecular level and compared it with our previous work in the intracellular infected Actinorhizal Plant Casuarina glauca. Immunolocalisation experiments showed that auxin accumulated in Frankia-infected cells in both systems. We then characterized the expression of auxin transporters in D. trinervis nodules. No activation of the heterologous CgAUX1 promoter was detected in infected cells in D. trinervis. These results were confirmed with the endogenous D. trinervis gene, DtAUX1. However, DtAUX1 was expressed in the nodule meristem. Consistently, transgenic D. trinervis Plants containing the auxin response marker DR5:VENUS showed expression of the reporter gene in the meristem. Immunolocalisation experiments using an antibody against the auxin efflux carrier PIN1, revealed the presence of this transporter in the plasma membrane of infected cells. Finally, we used in silico cellular models to analyse auxin fluxes in D. trinervis nodules. Our results point to the existence of divergent roles of auxin in intercellularly- and intracellularly-infected Actinorhizal Plants, an ancestral infection pathways leading to root nodule symbioses.
