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Effectors and Plant Immunity
Strategies of plant defense and microbe attacks
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Rescooped by Nicolas Denancé from Plants and Microbes
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YouTube: Plant interaction with friendly microorganisms gives pathogens their break (2012)

In two papers to be published in Current Biology, researchers from JIC and The Sainsbury Laboratory on the Norwich Research Park, and Rothamsted Research and the University of York identify genes that help plants interact with microbes in the soil.

 

Professor Giles Oldroyd of the John Innes Centre explains how plant roots form beneficial interactions with soil microbes. Almost all plants associate with mycorrhizal fungi to help in the uptake of nutrients such as phosphate. Some plants, particularly legumes, also associate with bacteria that ‘fix’ atmospheric nitrogen into a form the plant can use as fertiliser.

 

These two interactions are mediated within the plant by a common signalling pathway. The researchers have identified a specific mycorrhizal transcription factor. They also show how the signalling pathway has been recruited by pathogenic microbes, presenting a challenge to the plant. Its ability to form beneficial interactions can leave it vulnerable to invasion by pathogens.

 

Wang, E., Schornack, S., Marsh, J.F., Gobbato, E., Schwessinger, B., Eastmond, P., Schultze, M., Kamoun, S., and Oldroyd, G.E.D. (2012). A common signaling process that promotes mycorrhizal and oomycete colonization of plants. Curr. Biol. http://dx.doi.org/10.1016/j.cub.2012.09.043

 

Gobbato, E., Marsh, J.F., Vernie´ , T., Wang, E., Maillet, F., Kim, J., Miller, J.B., Sun, J., Bano, S.A., Ratet, P., et al. (2012). A GRAS-type transcription factor with a specific function in mycorrhizal signalling. Curr. Biol. http://dx.doi.org/10.1016/j.cub


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PLOS Pathogens (2012): Ustilago maydis: Dissecting the Molecular Interface between Pathogen and Plant

PLOS Pathogens (2012): Ustilago maydis: Dissecting the Molecular Interface between Pathogen and Plant | Effectors and Plant Immunity | Scoop.it

Fungal diseases of plants represent one of the most eminent threats to agriculture. Given the food needs of a growing world population and that more and more crops are devoted to fuel production, the necessity to develop crops with better resistance to disease is increasing. To accomplish this, the mechanisms that plant pathogenic fungi use to colonize plants need to be elucidated. As of now, there are only few examples/models in which this can be done on a functional, genome-wide level, taking into account both the pathogen and its host plant. The fungus Ustilago maydis (U. maydis) is one of these examples. It is a member of the smut fungi: a large group of parasites infecting mostly grasses, including several important crop plants such as maize, wheat, barley, and sugar cane. Smut fungi are biotrophs, i.e., parasites that need the living host plant to complete their sexual life cycle. They do not establish prominent feeding structures like the related, haustoria-forming rust fungi. During penetration, the host plasma membrane invaginates and completely encases the intracellular hyphae, establishing an extended interaction zone mediating the exchange of molecules between fungus and host. In contrast to most smut fungi that cause a systemic infection, remaining symptomless until the plant flowers, U. maydis can infect all above-ground parts of the maize plant but fails to spread systemically. U. maydis induces local tumors in which spores develop – a unique feature that allows detection of symptoms in corn seedlings less than a week after syringe infection with high levels of inoculum. This, together with the toolbox developed for reverse genetics, cell biology, and functional studies, has contributed to its status as a model for biotrophic basidiomycete fungi. Here the current level of our understanding of the elaborate molecular crosstalk between U. maydis and its host plant will be discussed.

 

Armin Djamei, Regine Kahman

 


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New Phytol. (2012): Identification of novel virulence genes and metabolic pathways required for full fitness of Pseudomonas savastanoi pv. savastanoi in olive (Olea europaea) knots

New Phytol. (2012): Identification of novel virulence genes and metabolic pathways required for full fitness of Pseudomonas savastanoi pv. savastanoi in olive (Olea europaea) knots | Effectors and Plant Immunity | Scoop.it

Comparative genomics and functional analysis of Pseudomonas syringae and related pathogens have mainly focused on diseases of herbaceous plants; however, there is a general lack of knowledge about the virulence and pathogenicity determinants required for infection of woody plants. Here, we applied signature-tagged mutagenesis (STM) to Pseudomonas savastanoi pv. savastanoi during colonization of olive (Olea europaea) knots, with the goal of identifying the range of genes linked to growth and symptom production in its plant host. A total of 58 different genes were identified, and most mutations resulted in hypovirulence in woody olive plants. Sequence analysis of STM mutations allowed us to identify metabolic pathways required for full fitness of P. savastanoi in olive and revealed novel mechanisms involved in the virulence of this pathogen, some of which are essential for full colonization of olive knots by the pathogen and for the lysis of host cells. This first application of STM to a P. syringae-like pathogen provides confirmation of functional capabilities long believed to play a role in the survival and virulence of this group of pathogens but not adequately tested before, and unravels novel factors not correlated previously with the virulence of other plant or animal bacterial pathogens.  

 

Isabel M. Matas, Lotte Lambertsen, Luis Rodríguez-Moreno, Cayo Ramos

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Plant J. (2012): Homologous RXLR effectors from Hyaloperonospora arabidopsidis and Phytophthora sojae suppress immunity in distantly related plants

Plant J. (2012): Homologous RXLR effectors from Hyaloperonospora arabidopsidis and Phytophthora sojae suppress immunity in distantly related plants | Effectors and Plant Immunity | Scoop.it

Diverse pathogens secrete effector proteins into plant cells to manipulate host cellular processes. Oomycete pathogens contain large complements of predicted effector genes defined by an RXLR host cell entry motif. The genome of Hyaloperonospora arabidopsidis (Hpa, downy mildew of Arabidopsis) contains at least 134 candidate RXLR effector genes. Only a small subset of these genes is conserved in related oomycetes from the Phytophthora genus. Here, we describe a comparative functional characterization of the Hpa RXLR effector gene HaRxL96 and a homologous gene, PsAvh163, from the Glycine max (soybean) pathogen Phytophthora sojae. HaRxL96 and PsAvh163 are induced during the early stages of infection and carry a functional RXLR motif that is sufficient for protein uptake into plant cells. Both effectors can suppress immune responses in soybean. HaRxL96 suppresses immunity in Nicotiana benthamiana, whereas PsAvh163 induces an HR-like cell death response in Nicotiana that is dependent on RAR1 and Hsp90.1. Transgenic Arabidopsis plants expressing HaRxL96 or PsAvh163 exhibit elevated susceptibility to virulent and avirulent Hpa, as well as decreased callose deposition in response to non-pathogenic Pseudomonas syringae. Both effectors interfere with defense marker gene induction, but do not affect salicylic acid biosynthesis. Together, these experiments demonstrate that evolutionarily conserved effectors from different oomycete species can suppress immunity in plant species that are divergent from the source pathogen’s host.

 

Ryan G. Anderson, Megan S. Casady, Rachel A. Fee, Martha M. Vaughan, Devdutta Deb, Kevin Fedkenheuer, Alisa Huffaker, Eric A. Schmelz, Brett M. Tyler, John M. McDowell

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Joseph Charlton's comment, October 27, 2012 6:44 PM
I am working on a similar idea with a serine/threonine receptor involved in powdery mildew resistance. The first transgenic shoots just appeared in tissue culture. Hopefully, I will be able to add to the list.
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Curr. Op. Microbiol. (2012): Genetic control of infection-related development in Magnaporthe oryzae

Curr. Op. Microbiol. (2012): Genetic control of infection-related development in Magnaporthe oryzae | Effectors and Plant Immunity | Scoop.it

Diseases caused by various pathogenic fungi pose a serious threat to global food security. Despite their differences in life cycles, fungal pathogens use well-conserved genetic mechanisms to regulate different developmental and infection processes. This review focuses on the key signaling pathways and recent advances in Magnaporthe oryzae, which is a model for studying fungal–plant interactions. In addition to the core components, a number of upstream genes and downstream targets of the cAMP–PKA and mitogen-activated protein (MAP) pathways have been identified. Recent advances in studies with cytoskeleton organization, effector biology, and ROS signaling in M. oryzae and future directions also are discussed.

 

Guotian Li, Xiaoying Zhou, Jin-Rong Xu


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Current Biology: A Common Signaling Process that Promotes Mycorrhizal and Oomycete Colonization of Plants (2012)

Current Biology: A Common Signaling Process that Promotes Mycorrhizal and Oomycete Colonization of Plants (2012) | Effectors and Plant Immunity | Scoop.it

The symbiotic association between plants and arbuscular mycorrhizal fungi is almost ubiquitous within the plant kingdom [1], and the early stages of the association are controlled by plant-derived strigolactone acting as a signal to the fungus in the rhizosphere [2–4] and lipochito-oligosaccharides acting as fungal signals to the plant [5]. Hyphopodia form at the root surface, allowing the initial invasion, and this is analogous to appressoria, infection structures of pathogenic fungi and oomycetes. Here, we characterize RAM2, a gene of Medicago truncatula required for colonization of the root by mycorrhizal fungi, which is necessary for appropriate hyphopodia and arbuscule formation. RAM2 encodes a glycerol-3-phosphate acyl transferase (GPAT) and is involved in the production of cutin monomers. Plants defective in RAM2 are unable to be colonized by arbuscular mycorrhizal fungi but also show defects in colonization by an oomycete pathogen, with the absence of appressoria formation. RAM2 defines a direct signaling function, because exogenous addition of the C16 aliphatic fatty acids associated with cutin are sufficient to promote hyphopodia/ appressoria formation. Thus, cutin monomers act as plant signals that promote colonization by arbuscular mycorrhizal fungi, and this signaling function has been recruited by pathogenic oomycetes to facilitate their own invasion.

 

Ertao Wang, Sebastian Schornack, John F. Marsh, Enrico Gobbato, Benjamin Schwessinger, Peter Eastmond, Michael Schultze, Sophien Kamoun, and Giles E.D. Oldroyd

 

http://kamounlab.dreamhosters.com/pdfs/CurrBiol_2012.pdf


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BMC Microb. (2012):Involvement of bacterial TonB-dependent signaling in the generation of an oligogalacturonide damage-associated molecular pattern from plant cell walls exposed to Xcc pectate lyases

BMC Microb. (2012):Involvement of bacterial TonB-dependent signaling in the generation of an oligogalacturonide damage-associated molecular pattern from plant cell walls exposed to Xcc pectate lyases | Effectors and Plant Immunity | Scoop.it

Efficient perception of attacking pathogens is essential for plants. Plant defense is evoked by molecules termed elicitors. Endogenous elicitors or damage-associated molecular patterns (DAMPs) originate from plant materials upon injury or pathogen activity. While there are comparably well-characterized examples for DAMPs, often oligogalacturonides (OGAs), generated by the activity of fungal pathogens, endogenous elicitors evoked by bacterial pathogens have been rarely described. In particular, the signal perception and transduction processes involved in DAMP generation are poorly characterized. A mutant strain of the phytopathogenic bacterium Xanthomonas campestris pv. campestris deficient in exbD2, which encodes a component of its unusual elaborate TonB system, had impaired pectate lyase activity and caused no visible symptoms for defense on the non-host plant pepper (Capsicum annuum). A co-incubation of X. campestris pv. campestris with isolated cell wall material from C. annuum led to the release of compounds which induced an oxidative burst in cell suspension cultures of the non-host plant. Lipopolysaccharides and proteins were ruled out as elicitors by polymyxin B and heat treatment, respectively. After hydrolysis with trifluoroacetic acid and subsequent HPAE chromatography, the elicitor preparation contained galacturonic acid, the monosaccharide constituent of pectate. OGAs were isolated from this crude elicitor preparation by HPAEC and tested for their biological activity. While small OGAs were unable to induce an oxidative burst, the elicitor activity in cell suspension cultures of the non-host plants tobacco and pepper increased with the degree of polymerization (DP). Maximal elicitor activity was observed for DPs exceeding 8. In contrast to the X. campestris pv. campestris wild type B100, the exbD2 mutant was unable to generate elicitor activity from plant cell wall material or from pectin. To our knowledge, this is the second report on a DAMP generated by bacterial features. The generation of the OGA elicitor is embedded in a complex exchange of signals within the framework of the plant-microbe interaction of C. annuum and X. campestris pv. campestris. The bacterial TonB-system is essential for the substrate-induced generation of extracellular pectate lyase activity. This is the first demonstration that a TonB-system is involved in bacterial trans-envelope signaling in the context of a pathogenic interaction with a plant.

 

Frank-Jörg Vorhölter, Heinrich-Günter Wiggerich, Heiko Scheidle, Vishaldeep Kaur Sidhu, Kalina Mrozek, Helge Küster, Alfred Pühler and Karsten Niehaus

 

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Nat. Commun. (2012): Tyrosine sulfation in a Gram-negative bacterium

Nat. Commun. (2012): Tyrosine sulfation in a Gram-negative bacterium | Effectors and Plant Immunity | Scoop.it

Tyrosine sulfation, a well-characterized post-translation modification in eukaryotes, has not previously been reported in prokaryotes. Here, we demonstrate that the RaxST protein from the Gram-negative bacterium, Xanthomonas oryzae pv. oryzae, is a tyrosine sulfotransferase. We used a newly developed sulfotransferase assay and ultraviolet photodissociation mass spectrometry to demonstrate that RaxST catalyses sulfation of tyrosine 22 of the Xoo Ax21 (activator of XA21-mediated immunity) protein. These results demonstrate a previously undescribed post-translational modification in a prokaryotic species with implications for studies of host immune responses and bacterial cell–cell communication systems.

 

Sang-Wook Han,Sang-Won Lee,Ofir Bahar,Benjamin Schwessinger,Michelle R. Robinson,Jared B. Shaw,James A. Madsen,Jennifer S. Brodbelt& Pamela C. Ronald

 

http://www.nature.com/ncomms/journal/v3/n10/full/ncomms2157.html

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PLoS ONE (2012): Chemical Communication between the Endophytic Fungus Paraconiothyrium Variabile and the Phytopathogen Fusarium oxysporum

PLoS ONE (2012): Chemical Communication between the Endophytic Fungus Paraconiothyrium Variabile and the Phytopathogen Fusarium oxysporum | Effectors and Plant Immunity | Scoop.it

Paraconiothyrium variabile, one of the specific endophytic fungi isolated from the host plant Cephalotaxus harringtonia, possesses the faculty to inhibit the growth of common phytopathogens, thus suggesting a role in its host protection. A strong antagonism between the endophyte P. variabile and Fusarium oxysporum was observed and studied using optic and electronic microscopies. A disorganization of the mycelium of F. oxysporum was thus noticed. Interestingly, the biological effect of the main secondary metabolites isolated from P. variabile against F. oxysporum did not account for this strong antagonism. However, a metabolomic approach of pure fungal strains and confrontation zones using the data analysis tool XCMS were analyzed and pointed out a competition-induced metabolite production by the endophyte in the presence of the phytopathogen. Subsequent MS/MS fragmentations permitted to identify one of the induced metabolites as 13-oxo-9,11-octadecadienoic acid and highlighted a negative modulation of the biosynthesis of beauvericin, one of the most potent mycotoxin of F. oxysporum, during the competition with the endophyte.

 

Audrey Combès, Idrissa Ndoye, Caroline Bance, Jérôme Bruzaud, Chakib Djediat, Joëlle Dupont, Bastien Nay, Soizic Prado

 

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New Phytol. (2012): TAL effectors targeting OsSWEET genes enhance virulence on diverse rice varieties when expressed individually in a TAL effector-deficient strain of X. oryzae

New Phytol. (2012): TAL effectors targeting OsSWEET genes enhance virulence on diverse rice varieties when expressed individually in a TAL effector-deficient strain of X. oryzae | Effectors and Plant Immunity | Scoop.it

Genomes of the rice (Oryza sativa) xylem and mesophyll pathogens Xanthomonas oryzae pv. oryzae (Xoo) and pv. oryzicola (Xoc) encode numerous secreted transcription factors called transcription activator-like (TAL) effectors. In a few studied rice varieties, some of these contribute to virulence by activating corresponding host susceptibility genes. Some activate disease resistance genes. The roles of X. oryzae TAL effectors in diverse rice backgrounds, however, are poorly understood. Xoo TAL effectors that promote infection by activating SWEET sucrose transporter genes were expressed in TAL effector-deficient X. oryzae strain X11-5A, and assessed in 21 rice varieties. Some were also tested in Xoc on variety Nipponbare. Several Xoc TAL effectors were tested in X11-5A on four rice varieties. Xoo TAL effectors enhanced X11-5A virulence on most varieties, but to varying extents depending on the effector and variety. SWEET genes were activated in all tested varieties, but increased virulence did not correlate with activation level. SWEET activators also enhanced Xoc virulence on Nipponbare. Xoc TAL effectors did not alter X11-5A virulence. SWEET-targeting TAL effectors contribute broadly and non-tissue-specifically to virulence in rice, and their function is affected by host differences besides target sequences. Further, the utility of X11-5A for characterizing individual TAL effectors in rice was established.

 

Valérie Verdier, Lindsay R. Triplett, Aaron W. Hummel, Rene Corral, R. Andres Cernadas, Clarice L. Schmidt, Adam J. Bogdanove, Jan E. Leach


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Nature: A soybean cyst nematode resistance gene points to a new mechanism of plant resistance to pathogens (2012)

Nature: A soybean cyst nematode resistance gene points to a new mechanism of plant resistance to pathogens (2012) | Effectors and Plant Immunity | Scoop.it

http://www.nature.com/nature/journal/vnfv/ncurrent/full/nature11651.html

 

Soybean (Glycine max (L.) Merr.) is an important crop that provides a sustainable source of protein and oil worldwide. Soybean cyst nematode (Heterodera glycines Ichinohe) is a microscopic roundworm that feeds on the roots of soybean and is a major constraint to soybean production. This nematode causes more than US$1 billion in yield losses annually in the United States alone1, making it the most economically important pathogen on soybean. Although planting of resistant cultivars forms the core management strategy for this pathogen, nothing is known about the nature of resistance. Moreover, the increase in virulent populations of this parasite on most known resistance sources necessitates the development of novel approaches for control. Here we report the map-based cloning of a gene at the Rhg4 (for resistance to Heterodera glycines 4) locus, a major quantitative trait locus contributing to resistance to this pathogen. Mutation analysis, gene silencing and transgenic complementation confirm that the gene confers resistance. The gene encodes a serine hydroxymethyltransferase, an enzyme that is ubiquitous in nature and structurally conserved across kingdoms. The enzyme is responsible for interconversion of serine and glycine and is essential for cellular one-carbon metabolism. Alleles of Rhg4 conferring resistance or susceptibility differ by two genetic polymorphisms that alter a key regulatory property of the enzyme. Our discovery reveals an unprecedented plant resistance mechanism against a pathogen. The mechanistic knowledge of the resistance gene can be readily exploited to improve nematode resistance of soybean, an increasingly important global crop.


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New Phytol. (2012): The key host for an invasive forest pathogen also facilitates the pathogen's survival of wildfire in California forests

New Phytol. (2012): The key host for an invasive forest pathogen also facilitates the pathogen's survival of wildfire in California forests | Effectors and Plant Immunity | Scoop.it

The first wildfires in sudden oak death-impacted forests occurred in 2008 in the Big Sur region of California, creating the rare opportunity to study the interaction between an invasive forest pathogen and a historically recurring disturbance. To determine whether and how the sudden oak death pathogen, Phytophthora ramorum, survived the wildfires, we completed intensive vegetation-based surveys in forest plots that were known to be infested before the wildfires. We then used 24 plot-based variables as predictors of P. ramorum recovery following the wildfires. The likelihood of recovering P. ramorum from burned plots was lower than in unburned plots both 1 and 2 yr following the fires. Post-fire recovery of P. ramorum in burned plots was positively correlated with the number of pre-fire symptomatic California bay laurel (Umbellularia californica), the key sporulating host for this pathogen, and negatively correlated with post-fire bay laurel mortality levels. Patchy burn patterns that left green, P. ramorum-infected bay laurel amidst the charred landscape may have allowed these trees to serve as inoculum reservoirs that could lead to the infection of newly sprouting vegetation, further highlighting the importance of bay laurel in the sudden oak death disease cycle.

 

Maia M. Beh, Margaret R. Metz, Kerri M. Frangioso, David M. Rizzo

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MPP: Xanthomonas campestris pv. campestris (cause of black rot of crucifers) in the genomic era is still a worldwide threat to brassica crops (2012)

MPP: Xanthomonas campestris pv. campestris (cause of black rot of crucifers) in the genomic era is still a worldwide threat to brassica crops (2012) | Effectors and Plant Immunity | Scoop.it

Background - Xanthomonas campestris pv. campestris (Xcc) (Pammel) Dowson is a Gram-negative bacterium that causes black rot, the most important disease of vegetable brassica crops worldwide. Intensive molecular investigation of Xcc is gaining momentum and several whole genome sequences are available.

 

Race structure, pathogenesis and epidemiology - Collections of Xcc isolates have been differentiated into physiological races based on the response of several brassica species lines. Black rot is a seed-borne disease. The disease is favoured by warm, humid conditions and can spread rapidly from rain dispersal and irrigation water.

 

Genome - The reference genomes of three isolates have been released. The genome consists of a single chromosome of approximately 5 100 000 bp, with a GC content of approximately 65% and an average predicted number of coding DNA sequences (CDS) of 4308.

 

Important genes identified - Three different secretion systems have been identified and studied in Xcc. The gene clusters xps and xcs encode a type II secretion system and xps genes have been linked to pathogenicity. The role of the type IV secretion system in pathogenicity is still uncertain. The hrp gene cluster encodes a type III secretion system that is associated with pathogenicity. An inventory of candidate effector genes has been assembled based on homology with known effectors. A range of other genes have been associated with virulence and pathogenicity, including the rpf, gum and wxc genes involved in the regulation of the synthesis of extracellular degrading enzymes, xanthan gum and lipopolysaccharides.

 

Useful website - http://www.xanthomonas.org

 

Joana G. Vicente, Eric B. Holub


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Now Live! Website for XVI IS-MPMI Congress, 6-10 July, 2014, Rhodes, Greece

Now Live! Website for XVI IS-MPMI Congress, 6-10 July, 2014, Rhodes, Greece | Effectors and Plant Immunity | Scoop.it

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Nucl. Acids Res. (2012): Iterative capped assembly: rapid and scalable synthesis of repeat-module DNA such as TAL effectors from individual monomers

Nucl. Acids Res. (2012): Iterative capped assembly: rapid and scalable synthesis of repeat-module DNA such as TAL effectors from individual monomers | Effectors and Plant Immunity | Scoop.it

DNA built from modular repeats presents a challenge for gene synthesis. We present a solid surface-based sequential ligation approach, which we refer to as iterative capped assembly (ICA), that adds DNA repeat monomers individually to a growing chain while using hairpin ‘capping’ oligonucleotides to block incompletely extended chains, greatly increasing the frequency of full-length final products. Applying ICA to a model problem, construction of custom transcription activator-like effector nucleases (TALENs) for genome engineering, we demonstrate efficient synthesis of TALE DNA-binding domains up to 21 monomers long and their ligation into a nuclease-carrying backbone vector all within 3 h. We used ICA to synthesize 20 TALENs of varying DNA target site length and tested their ability to stimulate gene editing by a donor oligonucleotide in human cells. All the TALENS show activity, with the ones >15 monomers long tending to work best. Since ICA builds full-length constructs from individual monomers rather than large exhaustive libraries of pre-fabricated oligomers, it will be trivial to incorporate future modified TALE monomers with improved or expanded function or to synthesize other types of repeat-modular DNA where the diversity of possible monomers makes exhaustive oligomer libraries impractical.

 

Adrian W. Briggs, Xavier Rios, Raj Chari, Luhan Yang, Feng Zhang, Prashant Mali and George M. Church


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Cellular Microb. (2012): Consequences of flagellin export through the type III secretion system of Pseudomonas syringae reveal a major difference in the innate immune systems of mammals and the mod...

Cellular Microb. (2012): Consequences of flagellin export through the type III secretion system of Pseudomonas syringae reveal a major difference in the innate immune systems of mammals and the mod... | Effectors and Plant Immunity | Scoop.it

Bacterial flagellin is perceived as a microbe (or pathogen)-associated molecular pattern (MAMP or PAMP) by the extracellular pattern recognition receptors, FLS2 and TLR5, of plants and mammals, respectively. Flagellin accidently translocated into mammalian cells by pathogen type III secretion systems (T3SSs) is recognized by nucleotide-binding leucine-rich repeat receptor NLRC4 as a pattern of pathogenesis and induces a death-associated immune response. The nonpathogen Pseudomonas fluorescens Pf0-1, expressing a Pseudomonas syringae T3SS, and the plant pathogen P. syringae pv. tomato DC3000 were used to seek evidence of an analogous cytoplasmic recognition system for flagellin in the model plant Nicotiana benthamiana. Flagellin (FliC) was secreted in culture and translocated into plant cells by the T3SS expressed in Pf0-1 and DC3000 and in their ΔflgGHI flagellar pathway mutants. ΔfliC and ΔflgGHI mutants of Pf0-1 and DC3000 were strongly reduced in elicitation of reactive oxygen species production and in immunity induction as indicated by the ability of challenge bacteria inoculated 6 h later to translocate a type III effector-reporter and to elicit effector-triggered cell death. Agrobacterium-mediated transient expression in N. benthamiana of FliC with or without a eukaryotic export signal peptide, coupled with virus-induced gene silencing of FLS2, revealed no immune response that was not FLS2 dependent. Transiently expressed FliC from DC3000 and Pectobacterium carotovorum did not induce cell death in N. benthamiana, tobacco, or tomato leaves. Flagellin is the major Pseudomonas MAMP perceived by N. benthamiana, and although flagellin secretion through the plant cell wall by the T3SS may partially contribute to FLS2-dependent immunity, flagellin in the cytosol does not elicit immune-associated cell death. We postulate that a death response to translocated MAMPs would produce vulnerability to the many necrotrophic pathogens of plants, such as P. carotovorum, which differ from P. syringae and other (hemi)biotrophic pathogens in benefitting from death-associated immune responses.

 

Hai-Lei Wei, Suma Chakravarthy, Jay N. Worley, Alan Collmer

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J. Exp. Bot. (2012): Microbial recognition and evasion of host immunity

J. Exp. Bot. (2012): Microbial recognition and evasion of host immunity | Effectors and Plant Immunity | Scoop.it

Plants are able to detect microbes by pattern recognition receptors in the host cells that, upon recognition of the enemy, activate effective immune responses in the invaded tissue. Recognition of microbes occurs by common conserved structures called microbe-associated molecular patterns (MAMPs). Plant pathogens and beneficial soil-borne microbes live in close contact with their host. Hence, prevention of the host’s defence programme is essential for their survival. Active suppression of host defences by microbial effector proteins is a well-known strategy employed by many successful plant-associated microbes. Evasion of host immune recognition is less well studied but is emerging as another important strategy. Escape from recognition by the host’s immune system can be caused by alterations in the structure of the recognized MAMPs, or by active intervention of ligand-receptor recognition. This paper reviews the structure and recognition of common MAMPs and the ways that plant-associated microbes have evolved to prevent detection by their host.


Michiel J. C. Pel and Corné M. J. Pieterse

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PLOS Genetics (2012): Specific Missense Alleles of the Arabidopsis Jasmonic Acid Co-Receptor COI1 Regulate Innate Immune Receptor Accumulation and Function

PLOS Genetics (2012): Specific Missense Alleles of the Arabidopsis Jasmonic Acid Co-Receptor COI1 Regulate Innate Immune Receptor Accumulation and Function | Effectors and Plant Immunity | Scoop.it

Plants utilize proteins containing nucleotide binding site (NB) and leucine-rich repeat (LRR) domains as intracellular innate immune receptors to recognize pathogens and initiate defense responses. Since mis-activation of defense responses can lead to tissue damage and even developmental arrest, proper regulation of NB–LRR protein signaling is critical. RAR1, SGT1, and HSP90 act as regulatory chaperones of pre-activation NB–LRR steady-state proteins. We extended our analysis of mutants derived from a rar1 suppressor screen and present two allelic rar1 suppressor (rsp) mutations of Arabidopsis COI1. Like all other coi1 mutations, coi1rsp missense mutations impair Jasmonic Acid (JA) signaling resulting in JA–insensitivity. However, unlike previously identified coi1 alleles, both coi1rsp alleles lack a male sterile phenotype. The coi1rsp mutants express two sets of disease resistance phenotypes. The first, also observed in coi1-1 null allele, includes enhanced basal defense against the virulent bacterial pathogen Pto DC3000 and enhanced effector-triggered immunity (ETI) mediated by the NB–LRR RPM1 protein in both rar1 and wild-type backgrounds. These enhanced disease resistance phenotypes depend on the JA signaling function of COI1. Additionally, the coi1rsp mutants showed a unique inability to properly regulate RPM1 accumulation and HR, exhibited increased RPM1 levels in rar1, and weakened RPM1-mediated HR in RAR1. Importantly, there was no change in the steady-state levels or HR function of RPM1 in coi1-1. These results suggest that the coi1rsp proteins regulate NB–LRR protein accumulation independent of JA signaling. Based on the phenotypic similarities and genetic interactions among coi1rsp, sgt1b, and hsp90.2rsp mutants, our data suggest that COI1 affects NB–LRR accumulation via two NB–LRR co-chaperones, SGT1b and HSP90. Together, our data demonstrate a role for COI1 in disease resistance independent of JA signaling and provide a molecular link between the JA and NB–LRR signaling pathways.

 

Yijian He, Eui-Hwan Chung, David A. Hubert, Pablo Tornero, Jeffery L. Dang

 

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Plant Cell (2012): Spatio-Temporal Cellular Dynamics of the Arabidopsis Flagellin Receptor Reveal Activation Status-Dependent Endosomal Sorting

Plant Cell (2012): Spatio-Temporal Cellular Dynamics of the Arabidopsis Flagellin Receptor Reveal Activation Status-Dependent Endosomal Sorting | Effectors and Plant Immunity | Scoop.it

The activity of surface receptors is location specific, dependent upon the dynamic membrane trafficking network and receptor-mediated endocytosis (RME). Therefore, the spatio-temporal dynamics of RME are critical to receptor function. The plasma membrane receptor FLAGELLIN SENSING2 (FLS2) confers immunity against bacterial infection through perception of flagellin (flg22). Following elicitation, FLS2 is internalized into vesicles. To resolve FLS2 trafficking, we exploited quantitative confocal imaging for colocalization studies and chemical interference. FLS2 localizes to bona fide endosomes via two distinct endocytic trafficking routes depending on its activation status. FLS2 receptors constitutively recycle in a Brefeldin A (BFA)–sensitive manner, while flg22-activated receptors traffic via ARA7/Rab F2b– and ARA6/Rab F1–positive endosomes insensitive to BFA. FLS2 endocytosis required a functional Rab5 GTPase pathway as revealed by dominant-negative ARA7/Rab F2b. Flg22-induced FLS2 endosomal numbers were increased by Concanamycin A treatment but reduced by Wortmannin, indicating that activated FLS2 receptors are targeted to late endosomes. RME inhibitors Tyrphostin A23 and Endosidin 1 altered but did not block induced FLS2 endocytosis. Additional inhibitor studies imply the involvement of the actin-myosin system in FLS2 internalization and trafficking. Altogether, we report a dynamic pattern of subcellular trafficking for FLS2 and reveal a defined framework for ligand-dependent endocytosis of this receptor.

 

Martina Beck, Ji Zhou, Christine Faulkner, Daniel MacLean and Silke Robatzek


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A really useful pathogen, Agrobacterium tumefaciens. New Teaching Tool.

A really useful pathogen, Agrobacterium tumefaciens. New Teaching Tool. | Effectors and Plant Immunity | Scoop.it

The soil bacterium Agrobacterium tumefaciens has a special place in plant biology. Through a rare inter-kingdom DNA transfer, the bacteria move some of their genes into their host's genome, thereby inducing the host cells to proliferate and produce opines, which are nutrients sources for the pathogen. Agrobacterium's ability to transfer DNA makes can be adapted to introduce other genes, such as those encoding useful traits, into plant genomes. The development of Agrobacterium as a tool to transform plants is a landmark event in modern plant biology. This new "Teaching Tool in Plant Biology" provides an introduction to Agrobacterium tumefaciens and related species, focusing on their modes of pathogenicity, their usefulness as tools for plant transformation, and their use as a model for the study of plant-pathogen interactions.

Find it here: http://www.plantcell.org/site/teachingtools/TTPB23.xhtml (subscription to Plant Cell or ASPB membership required).


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Lidia Pérez de Obanos's curator insight, November 27, 2013 6:15 AM

Agrobacterium tumefaciens es un vector muy útil para muchos tipos de genes que se quieren introducir en distintas plantas. Gracias a ella hemos podido realizar múltiples experimentos y es muy fácil de realizar.

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PLoS ONE (2012): Decay of Genes Encoding the Oomycete Flagellar Proteome in the Downy Mildew Hyaloperonospora arabidopsidis

PLoS ONE (2012): Decay of Genes Encoding the Oomycete Flagellar Proteome in the Downy Mildew Hyaloperonospora arabidopsidis | Effectors and Plant Immunity | Scoop.it

Zoospores are central to the life cycles of most of the eukaryotic microbes known as oomycetes, but some genera have lost the ability to form these flagellated cells. In the plant pathogen Phytophthora infestans, genes encoding 257 proteins associated with flagella were identified by comparative genomics. These included the main structural components of the axoneme and basal body, proteins involved in intraflagellar transport, regulatory proteins, enzymes for maintaining ATP levels, and others. Transcripts for over three-quarters of the genes were up-regulated during sporulation, and persisted to varying degrees in the pre-zoospore stage (sporangia) and motile zoospores. Nearly all of these genes had orthologs in other eukaryotes that form flagella or cilia, but not species that lack the organelle. Orthologs of 211 of the genes were also absent from a sister taxon to P. infestans that lost the ability to form flagella, the downy mildew Hyaloperonospora arabidopsidis. Many of the genes retained in H. arabidopsidis were also present in other non-flagellates, suggesting that they play roles both in flagella and other cellular processes. Remnants of the missing genes were often detected in the H. arabidopsidis genome. Degradation of the genes was associated with local compaction of the chromosome and a heightened propensity towards genome rearrangements, as such regions were less likely to share synteny with P. infestans.

 

Howard S. Judelson, Jolly Shrivastava, Joseph Manson

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Plant Cell (2012): Abscisic Acid Deficiency Antagonizes High-Temperature Inhibition of Disease Resistance through Enhancing Nuclear Accumulation of Resistance Proteins SNC1 and RPS4 in Arabidopsis

Plant Cell (2012): Abscisic Acid Deficiency Antagonizes High-Temperature Inhibition of Disease Resistance through Enhancing Nuclear Accumulation of Resistance Proteins SNC1 and RPS4 in Arabidopsis | Effectors and Plant Immunity | Scoop.it

Plant defense responses to pathogens are influenced by abiotic factors, including temperature. Elevated temperatures often inhibit the activities of disease resistance proteins and the defense responses they mediate. A mutant screen with an Arabidopsis thaliana temperature-sensitive autoimmune mutant bonzai1 revealed that the abscisic acid (ABA)–deficient mutant aba2 enhances resistance mediated by the resistance (R) gene SUPPRESSOR OF npr1-1 CONSTITUTIVE1 (SNC1) at high temperature. ABA deficiency promoted nuclear accumulation of SNC1, which was essential for it to function at low and high temperatures. Furthermore, the effect of ABA deficiency on SNC1 protein accumulation is independent of salicylic acid, whose effects are often antagonized by ABA. ABA deficiency also promotes the activity and nuclear localization of R protein RESISTANCE TO PSEUDOMONAS SYRINGAE4 at higher temperature, suggesting that the effect of ABA on R protein localization and nuclear activity is rather broad. By contrast, mutations that confer ABA insensitivity did not promote defense responses at high temperature, suggesting either tissue specificity of ABA signaling or a role of ABA in defense regulation independent of the core ABA signaling machinery. Taken together, this study reveals a new intersection between ABA and disease resistance through R protein localization and provides further evidence of antagonism between abiotic and biotic responses.

 

Hyung-Gon Mang, Weiqiang Qian, Ying Zhu, Jun Qian, Hong-Gu Kang, Daniel F. Klessig, and Jian Hua

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Cell Host and Microbe (2012): Phytopathogen Effectors Subverting Host Immunity: Different Foes, Similar Battleground

Cell Host and Microbe (2012): Phytopathogen Effectors Subverting Host Immunity: Different Foes, Similar Battleground | Effectors and Plant Immunity | Scoop.it

Phytopathogenic bacteria, fungi, and oomycetes invade and colonize their host plants through distinct routes. These pathogens secrete diverse groups of effector proteins that aid infection and establishment of different parasitic lifestyles. Despite this diversity, a comparison of different plant-pathogen systems has revealed remarkable similarities in the host immune pathways targeted by effectors from distinct pathogen groups. Immune signaling pathways mediated by pattern recognition receptors, phytohormone homeostasis or signaling, defenses associated with host secretory pathways and pathogen penetrations, and plant cell death represent some of the key processes controlling disease resistance against diverse pathogens. These immune pathways are targeted by effectors that carry a wide range of biochemical functions and are secreted by completely different pathogen groups, suggesting that these pathways are a common battleground encountered by many plant pathogens.

 

Daolong Dou, Jian-Min Zhou


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Ann. Rev. Cell Dev. Biology (2012): Hormonal Modulation of Plant Immunity

Ann. Rev. Cell Dev. Biology (2012): Hormonal Modulation of Plant Immunity | Effectors and Plant Immunity | Scoop.it

Plant hormones have pivotal roles in the regulation of plant growth, development, and reproduction. Additionally, they emerged as cellular signal molecules with key functions in the regulation of immune responses to microbial pathogens, insect herbivores, and beneficial microbes. Their signaling pathways are interconnected in a complex network, which provides plants with an enormous regulatory potential to rapidly adapt to their biotic environment and to utilize their limited resources for growth and survival in a cost-efficient manner. Plants activate their immune system to counteract attack by pathogens or herbivorous insects. Intriguingly, successful plant enemies evolved ingenious mechanisms to rewire the plant's hormone signaling circuitry to suppress or evade host immunity. Evidence is emerging that beneficial root-inhabiting microbes also hijack the hormone-regulated immune signaling network to establish a prolonged mutualistic association, highlighting the central role of plant hormones in the regulation of plant growth and survival.

 

Corné M.J. Pieterse, Dieuwertje Van der Does, Christos Zamioudis, Antonio Leon-Reyes, and Saskia C.M. Van Wees

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New Phytol. (2012): Biogeographical patterns and determinants of invasion by forest pathogens in Europe

New Phytol. (2012): Biogeographical patterns and determinants of invasion by forest pathogens in Europe | Effectors and Plant Immunity | Scoop.it

A large database of invasive forest pathogens (IFPs) was developed to investigate the patterns and determinants of invasion in Europe. Detailed taxonomic and biological information on the invasive species was combined with country-specific data on land use, climate, and the time since invasion to identify the determinants of invasiveness, and to differentiate the class of environments which share territorial and climate features associated with a susceptibility to invasion. IFPs increased exponentially in the last four decades. Until 1919, IFPs already present moved across Europe. Then, new IFPs were introduced mainly from North America, and recently from Asia. Hybrid pathogens also appeared. Countries with a wider range of environments, higher human impact or international trade hosted more IFPs. Rainfall influenced the diffusion rates. Environmental conditions of the new and original ranges and systematic and ecological attributes affected invasiveness. Further spread of established IFPs is expected in countries that have experienced commercial isolation in the recent past. Densely populated countries with high environmental diversity may be the weakest links in attempts to prevent new arrivals. Tight coordination of actions against new arrivals is needed. Eradication seems impossible, and prevention seems the only reliable measure, although this will be difficult in the face of global mobility.

 

A. Santini, L. Ghelardini, C. De Pace, M. L. Desprez-Loustau, P. Capretti, A. Chandelier, T. Cech, D. Chira, S. Diamandis, T. Gaitniekis, J. Hantula, O. Holdenrieder, L. Jankovsky, T. Jung, D. Jurc, T. Kirisits, A. Kunca, V. Lygis, M. Malecka, B. Marcais, S. Schmitz, J. Schumacher, H. Solheim, A. Solla, I. Szabò, P. Tsopelas, A. Vannini, A. M. Vettraino, J. Webber, S. Woodward and J. Stenlid

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