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Gene banks for wild and cultivated sunflower genetic resources | OCL - Oilseeds and fats, Crops and Lipids

Gene banks for wild and cultivated sunflower genetic resources | OCL - Oilseeds and fats, Crops and Lipids | LIPM_publications | Scoop.it
OCL, Oilseeds and fats, Crops and Lipids
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LCO Receptors Involved in Arbuscular Mycorrhiza Are Functional for Rhizobia Perception in Legumes - ScienceDirect

LCO Receptors Involved in Arbuscular Mycorrhiza Are Functional for Rhizobia Perception in Legumes - ScienceDirect | LIPM_publications | Scoop.it

Bacterial lipo-chitooligosaccharides (LCOs) are key mediators of the nitrogen-fixing root nodule symbiosis (RNS) in legumes. The isolation of LCOs from arbuscular mycorrhizal fungi suggested that LCOs are also signaling molecules in arbuscular mycorrhiza (AM). However, the corresponding plant receptors have remained uncharacterized. Here we show that petunia and tomato mutants in the LysM receptor-like kinases LYK10 are impaired in AM formation. Petunia and tomato LYK10 proteins have a high affinity for LCOs (Kd in the nM range) comparable to that previously reported for a legume LCO receptor essential for the RNS. Interestingly, the tomato and petunia LYK10 promoters, when introduced into a legume, were active in nodules similarly to the promoter of the legume orthologous gene. Moreover, tomato and petunia LYK10 coding sequences restored nodulation in legumes mutated in their orthologs. This combination of genetic and biochemical data clearly pinpoints Solanaceous LYK10 as part of an ancestral LCO perception system involved in AM establishment, which has been directly recruited during evolution of the RNS in legumes.

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Lipo‐chitooligosaccharides promote lateral root formation and modify auxin homeostasis in Brachypodium distachyon - Buendia - 2019 - New Phytologist

Lipo‐chitooligosaccharides promote lateral root formation and modify auxin homeostasis in Brachypodium distachyon - Buendia - 2019 - New Phytologist | LIPM_publications | Scoop.it

Lipo-chitooligosaccharides (LCOs) are microbial symbiotic signals that also influence root growth. In Medicago truncatula, LCOs stimulate lateral root formation (LRF) synergistically with auxin. However, the molecular mechanisms of this phenomenon and whether it is restricted to legume plants are not known. We have addressed the capacity of the model monocot Brachypodium distachyon (Brachypodium) to respond to LCOs and auxin for LRF. For this, we used a combination of root phenotyping assays, live-imaging and auxin quantification, and analysed the regulation of auxin homeostasis genes. We show that LCOs and a low dose of the auxin precursor indole-3-butyric acid (IBA) stimulated LRF in Brachypodium, while a combination of LCOs and IBA led to different regulations. Both LCO and IBA treatments locally increased endogenous indole-3-acetic acid (IAA) content, whereas the combination of LCO and IBA locally increased the endogenous concentration of a conjugated form of IAA (IAA-Ala). LCOs, IBA and the combination differentially controlled expression of auxin homeostasis genes. These results demonstrate that LCOs are active on Brachypodium roots and stimulate LRF probably through regulation of auxin homeostasis. The interaction between LCO and auxin treatments observed in Brachypodium on root architecture opens interesting avenues regarding their possible combined effects during the arbuscular mycorrhizal symbiosis.

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Chitotetraose activates the fungal-dependent endosymbiotic signaling pathway in actinorhizal plant species

Chitotetraose activates the fungal-dependent endosymbiotic signaling pathway in actinorhizal plant species | LIPM_publications | Scoop.it
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 intracellular 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 photosynthates. 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 Ca2+ reporter to identify symbiotic signaling responses to AM fungi in roots of both Casuarina glauca and Discaria trinervis, 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 chitotetraose is a more efficient elicitor of CSSP activation compared to AM fungal lipo-chitooligosaccharides. 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.
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The Nitrate Assimilatory Pathway in Sinorhizobium meliloti: Contribution to NO Production | Microbiology

The Nitrate Assimilatory Pathway in Sinorhizobium meliloti: Contribution to NO Production | Microbiology | LIPM_publications | Scoop.it
The interaction between rhizobia and their legume host plants culminates in the formation of specialized root organs called nodules in which differentiated endosymbiotic bacteria (bacteroids) fix atmospheric nitrogen to the benefit of the plant. Interestingly, nitric oxide (NO) has been detected at various steps of the rhizobium-legume symbiosis where it has been shown to play multifaceted roles. It is recognized that both bacterial and plant partners of the Sinorhizobium melilotiMedicago truncatula symbiosis are involved in NO synthesis in nodules. S. meliloti can also produce NO from nitrate when living as free cells in the soil. S. meliloti does not possess any NO synthase gene in its genome. Instead, the denitrification pathway is often described as the main driver of NO production with nitrate as substrate. This pathway includes the periplasmic nitrate reductase (Nap) which reduces nitrate into nitrite, and the nitrite reductase (Nir) which reduces nitrite into NO. However, additional genes encoding putative nitrate and nitrite reductases (called narB and nirB, respectively) have been identified in the S. meliloti genome. Here we examined the conditions where these genes are expressed, investigated their involvement in nitrate assimilation and NO synthesis in culture and their potential role in planta. We found that narB and nirB are expressed under aerobic conditions in absence of ammonium in the medium and most likely belong to the nitrate assimilatory pathway
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Spontaneous mutations in a regulatory gene induce phenotypic heterogeneity and adaptation of Ralstonia solanacearum to changing environments

Spontaneous mutations in a regulatory gene induce phenotypic heterogeneity and adaptation of Ralstonia solanacearum to changing environments | LIPM_publications | Scoop.it

An evolution experiment with the bacterial plant pathogen Ralstonia solanacearum revealed that several adaptive mutations conferring enhanced fitness in plants arose in the efpR gene encoding a regulator of virulence and metabolic functions. In this study, we found that an efpR mutant systematically displays colonies with two morphotypes: the type S (‘smooth’, similar to the wild type) and the type EV (‘efpR variant’). We demonstrated that the efpH gene, a homologue of efpR, plays a key role in the control of phenotypic heterogeneity, the ΔefpR‐ΔefpH double mutant being stably locked into the EV type. Using mixed infection assays, we demonstrated that the type EV is metabolically more proficient than the type S and displays fitness gain in specific environments, whereas the type S has a better fitness into the plant environment. We provide evidence that this efpR‐dependent phenotypic heterogeneity is a general feature of strains of the R. solanacearum species complex and could occur in natural conditions. This study highlights the potential role of phenotypic heterogeneity in this plant pathogen as an adaptive trait to changing environments.

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Mangroves in the Leaves: Anatomy, Physiology, and Immunity of Epithemal Hydathodes | Annual Review of Phytopathology

Mangroves in the Leaves: Anatomy, Physiology, and Immunity of Epithemal Hydathodes | Annual Review of Phytopathology | LIPM_publications | Scoop.it
Hydathodes are organs found on aerial parts of a wide range of plant species that provide almost direct access for several pathogenic microbes to the plant vascular system. Hydathodes are better known as the site of guttation, which is the release of droplets of plant apoplastic fluid to the outer leaf surface. Because these organs are only described through sporadic allusions in the literature, this review aims to provide a comprehensive view of hydathode development, physiology, and immunity by compiling a historic and contemporary bibliography. In particular, we refine the definition of hydathodes. We illustrate their important roles in the maintenance of plant osmotic balance, nutrient retrieval, and exclusion of deleterious chemicals from the xylem sap. Finally, we present our current understanding of the infection of hydathodes by adapted vascular pathogens and the associated plant immune responses.
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Pangenomic type III effector database of the plant pathogenic Ralstonia spp. [PeerJ]

Pangenomic type III effector database of the plant pathogenic Ralstonia spp. [PeerJ] | LIPM_publications | Scoop.it
Background The bacterial plant pathogenic Ralstonia species belong to the beta-proteobacteria class and are soil-borne pathogens causing vascular bacterial wilt disease, affecting a wide range of plant hosts. These bacteria form a heterogeneous group considered as a “species complex” gathering three newly defined species. Like many other Gram negative plant pathogens, Ralstonia pathogenicity relies on a type III secretion system, enabling bacteria to secrete/inject a large repertoire of type III effectors into their plant host cells. Type III-secreted effectors (T3Es) are thought to participate in generating a favorable environment for the pathogen (countering plant immunity and modifying the host metabolism and physiology). Methods Expert genome annotation, followed by specific type III-dependent secretion, allowed us to improve our Hidden-Markov-Model and Blast profiles for the prediction of type III effectors. Results We curated the T3E repertoires of 12 plant pathogenic Ralstonia strains, representing a total of 12 strains spread over the different groups of the species complex. This generated a pangenome repertoire of 102 T3E genes and 16 hypothetical T3E genes. Using this database, we scanned for the presence of T3Es in the 155 available genomes representing 140 distinct plant pathogenic Ralstonia strains isolated from different host plants in different areas of the globe. All this information is presented in a searchable database. A presence/absence analysis, modulated by a strain sequence/gene annotation quality score, enabled us to redefine core and accessory T3E repertoires.
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Role of the acquisition of a Type 3 Secretion System in the emergence of novel pathogenic strains of Xanthomonas

Cases of emergence of novel plant pathogenic strains are regularly reported that hinder yield of crops and trees. However the molecular mechanisms underlying such emergence are still poorly understood. The acquisition by environmental non‐pathogenic strains of novel virulence genes by horizontal gene transfer has been suggested as a driver for the emergence of novel pathogenic strains. In the present study, we tested such an hypothesis by transferring a plasmid encoding the Type 3 Secretion System (T3SS) and four associated Type 3 Secreted proteins (T3SPs) to the non‐pathogenic strains of Xanthomonas CFBP 7698 and CFBP 7700, that lack genes encoding T3SS and any previously known T3SPs. The resulting strains were phenotyped on Nicotiana benthamiana using chlorophyll fluorescence imaging and image analysis. Wild‐type non‐pathogenic strains induced a HR‐like necrosis, while strains complemented with the T3SS and T3SPs suppressed it. Such suppression depends on a functional T3SS. Among the T3SPs encoded on the plasmid, Hpa2, Hpa1, and to a lesser extend XopF1, collectively participate to the suppression. Monitoring the population sizes in planta showed that the sole acquisition of a functional T3SS by non‐pathogenic strains impairs growth inside leaf tissues. These results provide functional evidence that the acquisition via horizontal gene transfer of a T3SS and four T3SPs by environmental non‐pathogenic strains is not sufficient to make strains pathogenic. In the absence of canonical effector, the sole acquisition of a T3SS seems counter‐selected, and further acquisition of type 3 effectors is probably needed to allow the emergence of novel pathogenic strains.
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Medicago-Sinorhizobium-Ralstonia Co-infection Reveals Legume Nodules as Pathogen Confined Infection Sites Developing Weak Defenses

Medicago-Sinorhizobium-Ralstonia Co-infection Reveals Legume Nodules as Pathogen Confined Infection Sites Developing Weak Defenses | LIPM_publications | Scoop.it
Legume plants form root nodules, which host massive numbers of beneficial bacteria.
Benezech et al. show that the symbiotic organs are vulnerable to infection by pathogen
and that their defense ability is reduced. However, pathogens encounter confinement
in the nodules, which prevents them spreading to non-symbiotic parts of the plant.
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A receptor-like kinase enhances sunflower resistance to Orobanche cumana

A receptor-like kinase enhances sunflower resistance to Orobanche cumana | LIPM_publications | Scoop.it
Orobanche cumana (sunflower broomrape) is an obligate parasitic plant that infects sunflower roots, causing yield losses. Here, by using a map-based cloning strategy, we identified HaOr7—a gene that confers resistance to O. cumana race F—which was found to encode a leucine-rich repeat receptor-like kinase. The complete HAOR7 protein is present in resistant lines of sunflower and prevents O. cumana from connecting to the vascular system of sunflower roots, whereas susceptible lines encode a truncated protein that lacks transmembrane and kinase domains. Broomrape (Orobanche) is a parasitic plant that infects crops. Here, quantitative genetics and mapping in sunflower identify one resistance gene named HaOr7. It is a membrane receptor-like kinase that prevents attachment of the parasitic plant to the sunflower roots.
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Small RNAs from the plant pathogenic fungus Sclerotinia sclerotiorum highlight host candidate genes associated with quantitative disease resistance

Small RNAs from the plant pathogenic fungus Sclerotinia sclerotiorum highlight host candidate genes associated with quantitative disease resistance | LIPM_publications | Scoop.it
Fungal plant pathogens secrete effector proteins and metabolites to cause disease. Additionally, some species transfer small RNAs (sRNAs) into plant cells to silence host mRNAs through complementary base pairing and suppress plant immunity. The fungu
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A protein complex required for polar growth of rhizobial infection threads

A protein complex required for polar growth of rhizobial infection threads | LIPM_publications | Scoop.it
During root nodule symbiosis, intracellular accommodation of rhizobia by legumes is a prerequisite for nitrogen fixation. For many legumes, rhizobial colonization initiates in root hairs through transcellular infection threads. In Medicago truncatula
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Stress-inducible NHEJ in bacteria: function in DNA repair and acquisition of heterologous DNA | Nucleic Acids Research | Oxford Academic

Stress-inducible NHEJ in bacteria: function in DNA repair and acquisition of heterologous DNA | Nucleic Acids Research | Oxford Academic | LIPM_publications | Scoop.it

DNA double-strand breaks (DSB) in bacteria can be repaired by non-homologous end-joining (NHEJ), a two-component system relying on Ku and LigD. While performing a genetic characterization of NHEJ in Sinorhizobium meliloti, a representative of bacterial species encoding several Ku and LigD orthologues, we found that at least two distinct functional NHEJ repair pathways co-exist: one is dependent on Ku2 and LigD2, while the other depends on Ku3, Ku4 and LigD4. Whereas Ku2 likely acts as canonical bacterial Ku homodimers, genetic evidences suggest that Ku3-Ku4 form eukaryotic-like heterodimers. Strikingly, we found that the efficiency of both NHEJ systems increases under stress conditions, including heat and nutrient starvation. We found that this stimulation results from the transcriptional up-regulation of the ku and/or ligD genes, and that some of these genes are controlled by the general stress response regulator RpoE2. Finally, we provided evidence that NHEJ not only repairs DSBs, but can also capture heterologous DNA fragments into genomic breaks. Our data therefore suggest that NHEJ could participate to horizontal gene transfer from distantly related species, bypassing the need of homology to integrate exogenous DNA. This supports the hypothesis that NHEJ contributes to evolution and adaptation of bacteria under adverse environmental conditions.

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Introduction à la microbiologie - Microbiologie fondamentale et appliquée - Livre et ebook Sciences de la vie et santé de Luciano Paolozzi

Introduction à la microbiologie - Microbiologie fondamentale et appliquée - Livre et ebook Sciences de la vie et santé de Luciano Paolozzi | LIPM_publications | Scoop.it
En couleur et très illustré, cette introduction à la microbiologie s'articule en trois parties. La première partie, "Microbiologie fondamentale", est une présentation générale des micro-organismes, de leur classification à leur physiologi
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The Ptr1 Locus of Solanum lycopersicoides Confers Resistance to Race 1 Strains of Pseudomonas syringae pv. tomato and to Ralstonia pseudosolanacearum by Recognizing the Type III Effectors AvrRpt2 a...

The Ptr1 Locus of Solanum lycopersicoides Confers Resistance to Race 1 Strains of Pseudomonas syringae pv. tomato and to Ralstonia pseudosolanacearum by Recognizing the Type III Effectors AvrRpt2 a... | LIPM_publications | Scoop.it

Race 1 strains of Pseudomonas syringae pv. tomato, which cause bacterial speck disease of tomato, are becoming increasingly common and no simply inherited genetic resistance to such strains is known. We discovered that a locus in Solanum lycopersicoides, termed Pseudomonas tomato race 1 (Ptr1), confers resistance to race 1 P. syringae pv. tomato strains by detecting the activity of type III effector AvrRpt2. In Arabidopsis, AvrRpt2 degrades the RIN4 protein, thereby activating RPS2-mediated immunity. Using site-directed mutagenesis of AvrRpt2, we found that, like RPS2, activation of Ptr1 requires AvrRpt2 proteolytic activity. Ptr1 also detected the activity of AvrRpt2 homologs from diverse bacteria, including one in Ralstonia pseudosolanacearum. The genome sequence of S. lycopersicoides revealed no RPS2homolog in the Ptr1 region. Ptr1 could play an important role in controlling bacterial speck disease and its future cloning may shed light on an example of convergent evolution for recognition of a widespread type III effector.

 

https://doi.org/10.1094/MPMI-01-19-0018-R

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Two ancestral genes shaped the Xanthomonas campestris TAL effector gene repertoire

Two ancestral genes shaped the Xanthomonas campestris TAL effector gene repertoire | LIPM_publications | Scoop.it
Xanthomonas transcription activator‐like effectors (TALEs) are injected inside plant cells to promote host susceptibility by enhancing transcription of host susceptibility genes. TALE‐encoding (tal) genes were thought to be absent from Brassicaceae‐infecting Xanthomonas campestris (Xc) genomes based on four reference genomic sequences. We discovered tal genes in 26 of 49 Xc strains isolated worldwide and used a combination of single molecule real time (SMRT) and tal amplicon sequencing to yield a near‐complete description of the TALEs found in Xc (Xc TALome). The 53 sequenced tal genes encode 21 distinct DNA binding domains that sort into seven major DNA binding specificities. In silico analysis of the Brassica rapa promoterome identified a repertoire of predicted TALE targets, five of which were experimentally validated using quantitative reverse transcription polymerase chain reaction. The Xc TALome shows multiple signs of DNA rearrangements that probably drove its evolution from two ancestral tal genes. We discovered that Tal12a and Tal15a of Xcc strain Xca5 contribute together in the development of disease symptoms on susceptible B. oleracea var. botrytis cv Clovis. This large and polymorphic repertoire of TALEs opens novel perspectives for elucidating TALE‐mediated susceptibility of Brassicaceae to black rot disease and for understanding the molecular processes underlying TALE evolution.
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Spatio-temporal control of mutualism in legumes helps spread symbiotic nitrogen fixation

Spatio-temporal control of mutualism in legumes helps spread symbiotic nitrogen fixation | LIPM_publications | Scoop.it
Mutualism is of fundamental importance in ecosystems. Which factors help to keep the relationship mutually beneficial and evolutionarily successful is a central question. We addressed this issue for one of the most significant mutualistic interaction
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