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Publications from The Sainsbury Laboratory
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eLIFE: Evidence for suppression of immunity as a driver for genomic introgressions and host range expansion in races of Albugo candida, a generalist parasite (2015)

eLIFE: Evidence for suppression of immunity as a driver for genomic introgressions and host range expansion in races of Albugo candida, a generalist parasite (2015) | Publications from The Sainsbury Laboratory | Scoop.it
The Sainsbury Lab's insight:

How generalist parasites with wide host ranges can evolve is a central question in parasite evolution. Albugo candida is an obligate biotrophic parasite that consists of many physiological races that each specialize on distinct Brassicaceae host species. By analyzing genome sequence assemblies of five isolates, we show they represent three races that are genetically diverged by ~1%. Despite this divergence, their genomes are mosaic-like, with ~25% being introgressed from other races. Sequential infection experiments show that infection by adapted races enables subsequent infection of hosts by normally non-infecting races. This facilitates introgression and the exchange of effector repertoires, and may enable the evolution of novel races that can undergo clonal population expansion on new hosts. We discuss recent studies on hybridization in other eukaryotes such as yeast, Heliconius butterflies, Darwin's finches, sunflowers and cichlid fishes, and the implications of introgression for pathogen evolution in an agro-ecological environment. - See more at: http://elifesciences.org/content/early/2015/02/27/eLife.04550/article-data#.dpuf

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PLoS Pathogens: The Phylogenetically-Related Pattern Recognition Receptors EFR and XA21 Recruit Similar Immune Signaling Components in Monocots and Dicots (2015)

PLoS Pathogens: The Phylogenetically-Related Pattern Recognition Receptors EFR and XA21 Recruit Similar Immune Signaling Components in Monocots and Dicots (2015) | Publications from The Sainsbury Laboratory | Scoop.it

Pests and diseases cause significant agricultural losses. Plants recognize pathogen-derived molecules via plasma membrane-localized immune receptors (called pattern recognition receptors or PRRs), resulting in pathogen resistance. In recent years, the transfer of PRRs across plant species has emerged as a promising biotechnological approach to improve crop disease resistance. Successful transfers of PRRs suggest that immune signaling components are conserved across plant species. In this study, we demonstrate that the PRR XA21 from the monocot plant rice is functional in the dicot plant Arabidopsis thaliana (Arabidopsis) and that it confers quantitatively enhanced resistance to bacteria. Furthermore, we show that the rice XA21 and the Arabidopsis EFR, which are evolutionary-distant but phylogenetically closely related, recruit similar signaling components for their function, revealing an overall conservation of immune pathways across monocots and dicots. These findings demonstrate evolutionary conservation of downstream signaling from PRRs and indicate that transfer of PRRs is possible between different plant families, but also between monocots and dicots.

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Molecular Plant-Microbe Interactions: Journal - 0(ja): 14-3-3 proteins in plant-pathogen interactions (2015)

Molecular Plant-Microbe Interactions:  Journal - 0(ja): 14-3-3 proteins in plant-pathogen interactions (2015) | Publications from The Sainsbury Laboratory | Scoop.it
The Sainsbury Lab's insight:

14-3-3 proteins define a eukaryotic-specific protein family with a general role in signal transduction. Primarily, 14-3-3 proteins act as phospho-sensors, binding phosphorylated client proteins and modulating their functions. Since phosphorylation regulates a plethora of different physiological responses in plants, 14-3-3 proteins play roles in multiple signalling pathways, including those controlling metabolism, hormone signalling, cell division, and responses to abiotic and biotic stimuli. Increasing evidence supports a prominent role of 14-3-3 proteins in regulating plant immunity against pathogens at various levels. In this review, potential links between 14-3-3 function and the regulation of plant-pathogen interactions are discussed, with a special focus on the regulation of 14-3-3s in response to pathogen perception, interactions between 14-3-3s and defence-related proteins, and 14-3-3s as targets of pathogen effectors.

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Frontiers in Plant Sci: Strategies for transferring resistance into wheat: from wide crosses to GM cassettes (2014)

Frontiers in Plant Sci: Strategies for transferring resistance into wheat: from wide crosses to GM cassettes (2014) | Publications from The Sainsbury Laboratory | Scoop.it
The domestication of wheat in the Fertile Crescent 10,000 years ago led to a genetic bottleneck. Modern agriculture has further narrowed the genetic base by introducing extreme levels of uniformity...
The Sainsbury Lab's insight:

The domestication of wheat in the Fertile Crescent 10,000 years ago led to a genetic bottleneck. Modern agriculture has further narrowed the genetic base by introducing extreme levels of uniformity on a vast spatial and temporal scale. This reduction in genetic complexity renders the crop vulnerable to new and emerging pests and pathogens. The wild relatives of wheat represent an important source of genetic variation for disease resistance. For nearly a century farmers, breeders, and cytogeneticists have sought to access this variation for crop improvement. Several barriers restricting interspecies hybridization and introgression have been overcome, providing the opportunity to tap an extensive reservoir of genetic diversity. Resistance has been introgressed into wheat from at least 52 species from 13 genera, demonstrating the remarkable plasticity of the wheat genome and the importance of such natural variation in wheat breeding. Two main problems hinder the effective deployment of introgressed resistance genes for crop improvement: (1) the simultaneous introduction of genetically linked deleterious traits and (2) the rapid breakdown of resistance when deployed individually. In this review, we discuss how recent advances in molecular genomics are providing new opportunities to overcome these problems.

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Traffic: Rerouting of plant late endocytic trafficking towards a pathogen interface (2014)

Traffic: Rerouting of plant late endocytic trafficking towards a pathogen interface (2014) | Publications from The Sainsbury Laboratory | Scoop.it
The Sainsbury Lab's insight:

A number of plant pathogenic and symbiotic microbes produce specialized cellular structures that invade host cells where they remain enveloped by host-derived membranes. The mechanisms underlying the biogenesis and functions of host-microbe interfaces are poorly understood. Here, we show that plant late endocytic trafficking is diverted towards the extrahaustorial membrane; a host-pathogen interface that develops in plant cells invaded by Irish potato famine pathogen Phytophthora infestans. A late endosome and tonoplast marker protein Rab7

GTPase RabG3c, but not a tonoplast-localized sucrose transporter, is recruited to the extrahaustorial membrane suggesting specific rerouting of vacuole targeted late endosomes to a host pathogen interface. We revealed the dynamic nature of this process by showing that, upon activation, a cell surface immune receptor traffics towards the haustorial interface. Our work provides insight into the biogenesis of the extrahaustorial membrane and reveals dynamic processes that recruit membrane compartments and immune receptors to this host-pathogen interface.

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Curr Opinion in Microbiology: Targeting of plant pattern recognition receptor-triggered immunity by bacterial type-III secretion system effectors (2014)

Curr Opinion in Microbiology: Targeting of plant pattern recognition receptor-triggered immunity by bacterial type-III secretion system effectors (2014) | Publications from The Sainsbury Laboratory | Scoop.it
The Sainsbury Lab's insight:

During infection, microbes are detected by surface-localized pattern recognition receptors (PRRs), leading to an innate immune response that prevents microbial ingress. Therefore, successful pathogens must evade or inhibit PRR-triggered immunity to cause disease. In the past decade, a number of type-III secretion system effector (T3Es) proteins from plant pathogenic bacteria have been shown to suppress this layer of innate immunity. More recently, the detailed mechanisms of action have been defined for several of these effectors. Interestingly, effectors display a wide array of virulence targets, being able to prevent activation of immune receptors and to hijack immune signaling pathways. Besides being a fascinating example of pathogen-host co-evolution, effectors have also emerged as valuable tools to dissect important biological processes in host cells.

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Cell Host & Microbe: The Calcium-Dependent Protein Kinase CPK28 Buffers Plant Immunity and Regulates BIK1 Turnover (2014)

Cell Host & Microbe: The Calcium-Dependent Protein Kinase CPK28 Buffers Plant Immunity and Regulates BIK1 Turnover (2014) | Publications from The Sainsbury Laboratory | Scoop.it
The Sainsbury Lab's insight:

Plant perception of pathogen-associated molecular patterns (PAMPs) triggers a phosphorylation relay leading to PAMP-triggered immunity (PTI). Despite increasing knowledge of PTI signaling, how immune homeostasis is maintained remains largely unknown. Here we describe a forward-genetic screen to identify loci involved in PTI and characterize the Arabidopsis calcium-dependent protein kinase CPK28 as a negative regulator of immune signaling. Genetic analyses demonstrate that CPK28 attenuates PAMP-triggered immune responses and antibacterial immunity. CPK28 interacts with and phosphorylates the plasma-membrane-associated cytoplasmic kinase BIK1, an important convergent substrate of multiple pattern recognition receptor (PRR) complexes. We find that BIK1 is rate limiting in PTI signaling and that it is continuously turned over to maintain cellular homeostasis. We further show that CPK28 contributes to BIK1 turnover. Our results suggest a negative regulatory mechanism that continually buffers immune signaling by controlling the turnover of this key signaling kinase.

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PLOS Genetics: The Nuclear Immune Receptor RPS4 Is Required for RRS1SLH1-Dependent Constitutive Defense Activation in Arabidopsis thaliana (2014)

PLOS Genetics: The Nuclear Immune Receptor RPS4 Is Required for RRS1SLH1-Dependent Constitutive Defense Activation in Arabidopsis thaliana (2014) | Publications from The Sainsbury Laboratory | Scoop.it
PLOS Genetics is an open-access
The Sainsbury Lab's insight:

Plant nucleotide-binding leucine-rich repeat (NB-LRR) disease resistance (R) proteins recognize specific “avirulent” pathogen effectors and activate immune responses. NB-LRR proteins structurally and functionally resemble mammalian Nod-like receptors (NLRs). How NB-LRR and NLR proteins activate defense is poorly understood. The divergently transcribed Arabidopsis R genes, RPS4 (resistance to Pseudomonas syringae 4) and RRS1 (resistance to Ralstonia solanacearum 1), function together to confer recognition of Pseudomonas AvrRps4 and Ralstonia PopP2. RRS1 is the only known recessive NB-LRR R gene and encodes a WRKY DNA binding domain, prompting suggestions that it acts downstream of RPS4 for transcriptional activation of defense genes. We define here the early RRS1-dependent transcriptional changes upon delivery of PopP2 via Pseudomonas type III secretion. The Arabidopsis slh1 (sensitive to low humidity 1) mutant encodes an RRS1 allele (RRS1SLH1) with a single amino acid (leucine) insertion in the WRKY DNA-binding domain. Its poor growth due to constitutive defense activation is rescued at higher temperature. Transcription profiling data indicate that RRS1SLH1-mediated defense activation overlaps substantially with AvrRps4- and PopP2-regulated responses. To better understand the genetic basis of RPS4/RRS1-dependent immunity, we performed a genetic screen to identify suppressor of slh1 immunity (sushi) mutants. We show that many sushi mutants carry mutations in RPS4, suggesting that RPS4 acts downstream or in a complex with RRS1. Interestingly, several mutations were identified in a domain C-terminal to the RPS4 LRR domain. Using an Agrobacterium-mediated transient assay system, we demonstrate that the P-loop motif of RPS4 but not of RRS1SLH1 is required for RRS1SLH1 function. We also recapitulate the dominant suppression of RRS1SLH1 defense activation by wild type RRS1 and show this suppression requires an intact RRS1 P-loop. These analyses of RRS1SLH1 shed new light on mechanisms by which NB-LRR protein pairs activate defense signaling, or are held inactive in the absence of a pathogen effector.

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Plant Journal: Probing formation of cargo/importin-α transport complexes in plant cells using a pathogen effector (2014)

Plant Journal: Probing formation of cargo/importin-α transport complexes in plant cells using a pathogen effector (2014) | Publications from The Sainsbury Laboratory | Scoop.it
The Sainsbury Lab's insight:

Importin-αs are essential adapter proteins that recruit cytoplasmic proteins destined for active nuclear import to the nuclear transport machinery. Cargo proteins interact with the importin-α armadillo repeat domain via nuclear localization sequences (NLSs), short amino acids motifs enriched in Lys and Arg residues. Plant genomes typically encode several importin-α paralogs that can have both specific and partially redundant functions. Although some cargos are preferentially imported by a distinct importin-α, it remains unknown how this specificity is generated and to what extent cargos compete for binding to nuclear transport receptors. Here we report that the effector protein HaRxL106 from the oomycete pathogen Hyaloperonospora arabidopsidis co-opts the host cell's nuclear import machinery. We use HaRxL106 as a probe to determine redundant and specific functions of importin-α paralogs from Arabidopsis thaliana. A crystal structure of the importin-α3/MOS6 armadillo repeat domain suggests that five of the six Arabidopsis importin-αs expressed in rosette leaves have an almost identical NLS binding site. Comparison of the importin-α binding affinities of HaRxL106 and other cargos in vitro and in plant cells suggests that relatively small affinity differences in vitro affect the rate of transport complex formation in vivo. Our results suggest that cargo affinity for importin-α, sequence variation at the importin-α NLS binding sites and tissue-specific expression levels of importin-αs determine formation of cargo/importin-α transport complexes in plant cells.

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Trends Plant Sci: Trade-off between growth and immunity: role of brassinosteroids (2014)

Trends Plant Sci: Trade-off between growth and immunity: role of brassinosteroids (2014) | Publications from The Sainsbury Laboratory | Scoop.it
The Sainsbury Lab's insight:

A balance between growth and immunity exists in plants. Recently, the growth-promoting hormones brassinosteroids (BR) have emerged as crucial regulators of the growth-immunity trade-off, although the molecular mechanisms underlying this role remained unclear. New evidence obtained from the model plant Arabidopsis thaliana points at an indirect crosstalk between BR signaling and immunity, mediated by the transcription factors BZR1 and HBI1, which suppress immunity upon BR perception. The core transcriptional cascade formed by BZR1 and HBI1 seems to act as a regulatory hub on which multiple signaling inputs impinge, ensuring effective fine-tuning of the trade-off between growth and immunity in a timely and cost-efficient manner.

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Cell Host & Microbe: Convergent Targeting of a Common Host Protein-Network by Pathogen Effectors from Three Kingdoms of Life (2014)

Cell Host & Microbe: Convergent Targeting of a Common Host Protein-Network by Pathogen Effectors from Three Kingdoms of Life (2014) | Publications from The Sainsbury Laboratory | Scoop.it
The Sainsbury Lab's insight:

Highlights

 

 - Powdery mildew fungus G. orontii virulence effectors and their host-interactors identified

 - Integrated network map reveals interspecies effector convergence onto shared host proteins

 - Mutants of convergent effector-targeted host proteins display altered infection phenotypes

 - Host genes under balancing selection encode indirect targets of pathogen effectors

 

Summary

While conceptual principles governing plant immunity are becoming clear, its systems-level organization and the evolutionary dynamic of the host-pathogen interface are still obscure. We generated a systematic protein-protein interaction network of virulence effectors from the ascomycete pathogen Golovinomyces orontii and Arabidopsis thaliana host proteins. We combined this data set with corresponding data for the eubacterial pathogen Pseudomonas syringae and the oomycete pathogen Hyaloperonospora arabidopsidis. The resulting network identifies host proteins onto which intraspecies and interspecies pathogen effectors converge. Phenotyping of 124 Arabidopsis effector-interactor mutants revealed a correlation between intraspecies and interspecies convergence and several altered immune response phenotypes. Several effectors and the most heavily targeted host protein colocalized in subnuclear foci. Products of adaptively selected Arabidopsis genes are enriched for interactions with effector targets. Our data suggest the existence of a molecular host-pathogen interface that is conserved across Arabidopsis accessions, while evolutionary adaptation occurs in the immediate network neighborhood of effector targets.

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PLOS ONE: Variation in Capsidiol Sensitivity between Phytophthora infestans and Phytophthora capsici Is Consistent with Their Host Range (2014)

PLOS ONE: Variation in Capsidiol Sensitivity between Phytophthora infestans and Phytophthora capsici Is Consistent with Their Host Range (2014) | Publications from The Sainsbury Laboratory | Scoop.it
PLOS ONE: an inclusive, peer-reviewed, open-access resource from the PUBLIC LIBRARY OF SCIENCE. Reports of well-performed scientific studies from all disciplines freely available to the whole world.
The Sainsbury Lab's insight:

Plants protect themselves against a variety of invading pathogenic organisms via sophisticated defence mechanisms. These responses include deployment of specialized antimicrobial compounds, such as phytoalexins, that rapidly accumulate at pathogen infection sites. However, the extent to which these compounds contribute to species-level resistance and their spectrum of action remain poorly understood. Capsidiol, a defense related phytoalexin, is produced by several solanaceous plants including pepper and tobacco during microbial attack. Interestingly, capsidiol differentially affects growth and germination of the oomycete pathogensPhytophthora infestans and Phytophthora capsici, although the underlying molecular mechanisms remain unknown. In this study we revisited the differential effect of capsidiol on P. infestans and P. capsici, using highly pure capsidiol preparations obtained from yeast engineered to express the capsidiol biosynthetic pathway. Taking advantage of transgenicPhytophthora strains expressing fluorescent markers, we developed a fluorescence-based method to determine the differential effect of capsidiol on Phytophtora growth. Using these assays, we confirm major differences in capsidiol sensitivity between P. infestans and P. capsici and demonstrate that capsidiol alters the growth behaviour of both Phytophthoraspecies. Finally, we report intraspecific variation within P. infestans isolates towards capsidiol tolerance pointing to an arms race between the plant and the pathogens in deployment of defence related phytoalexins.

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Frontiers: Effector proteins of rust fungi (2014)

Frontiers: Effector proteins of rust fungi (2014) | Publications from The Sainsbury Laboratory | Scoop.it
Rust fungi include many species that are devastating crop pathogens. To develop resistant plants, a better understanding of rust virulence factors, or effector proteins, is needed. Thus far, only six rust effector proteins have been described: AvrP123, AvrP4, AvrL567, AvrM, RTP1 and PGTAUSPE-10-1. Although some are well established model proteins used to investigate mechanisms of immune receptor activation (avirulence activities) or entry into plant cells, how they work inside host tissues to promote fungal growth remains unknown. The genome sequences of four rust fungi (two Melampsoraceae and two Pucciniaceae) have been analyzed so far. Genome-wide analyses of these species, as well as transcriptomics performed on a broader range of rust fungi, revealed hundreds of small secreted proteins considered as rust candidate secreted effector proteins (CSEPs). The rust community now needs high-throughput approaches (effectoromics) to accelerate effector discovery/characterization and to better understand how they function in planta. However, this task is challenging due to the non-amenability of rust pathosystems (obligate biotrophs infecting crop plants) to traditional molecular genetic approaches mainly due to difficulties in culturing these species in vitro. The use of heterologous approaches should be promoted in the future.
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Molecular Plant-Microbe Interactions: Candidate Effector Proteins of the Rust Pathogen Melampsora Larici-Populina Target Diverse Plant Cell Compartments (2015)

Molecular Plant-Microbe Interactions: Candidate Effector Proteins of the Rust Pathogen Melampsora Larici-Populina Target Diverse Plant Cell Compartments (2015) | Publications from The Sainsbury Laboratory | Scoop.it
The Sainsbury Lab's insight:

Rust fungi are devastating crop pathogens that deliver effector proteins into infected tissues to modulate plant functions and promote parasitic growth. The genome of the poplar leaf rust fungus Melampsora larici-populina revealed a large catalogue of secreted proteins, some of which have been considered candidate effectors. Unravelling how these proteins function in host cells is key to understanding pathogenicity mechanisms and developing resistant plants. In this study, we used an effectoromics pipeline to select, clone, and express 20 candidate effectors in Nicotiana benthamiana leaf cells to determine their subcellular localisation and identify the plant proteins they interact with. Confocal microscopy revealed that six candidate effectors target the nucleus, nucleoli, chloroplasts, mitochondria and discrete cellular bodies. We also used coimmunoprecipitation and mass spectrometry to identify 606 N. benthamiana proteins that associate with the candidate effectors. Five candidate effectors specifically associated with a small set of plant proteins that may represent biologically relevant interactors. We confirmed the interaction between the candidate effector MLP124017 and the TOPLESS-Related Protein 4 from poplar by in planta coimmunoprecipitation. Altogether, our data enable us to validate effector proteins from M. larici-populina and reveal that these proteins may target multiple compartments and processes in plant cells. It also shows that N. benthamiana can be a powerful heterologous system to study effectors of obligate biotrophic pathogens.

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Bioinformatics: NLR-parser: Rapid annotation of plant NLR complements (2015)

Bioinformatics: NLR-parser: Rapid annotation of plant NLR complements (2015) | Publications from The Sainsbury Laboratory | Scoop.it
The Sainsbury Lab's insight:

Motivation: The repetitive nature of plant disease resistance genes encoding for nucleotide-binding leucine-rich repeat (NLR) proteins hampers their prediction with standard gene annotation software. Mast has previously been reported as a tool to support annotation of NLR-encoding genes. However the decision if a motif combination represents an NLR protein was entirely manual.
Results: The NLR-parser pipeline is designed to use the MAST output from six-frame translated amino acid sequences and filters for predefined biologically curated motif compositions. Input reads can be derived from, for example, raw long read sequencing data or contigs and scaffolds coming from plant genome projects. The out- put is a tab-separated file with information on start and frame of the first NLR specific motif, whether the identified sequence is a TNL or CNL, potentially full or fragmented. In addition, the output of the NB- ARC domain sequence can directly be used for phylogenetic anal- yses. In comparison to other prediction software, the highly complex NB-ARC domain is described in detail using several individual mo- tifs.

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Plant Methods: Mapping mutations in plant genomes with the user-friendly web application CandiSNP (2014)

Plant Methods: Mapping mutations in plant genomes with the user-friendly web application CandiSNP (2014) | Publications from The Sainsbury Laboratory | Scoop.it
The Sainsbury Lab's insight:

Analysis of mutants isolated from forward-genetic screens has revealed key components of several plant signalling pathways. Mapping mutations by position, either using classical methods or whole genome high-throughput sequencing (HTS), largely relies on the analysis of genome-wide polymorphisms in F2 recombinant populations. Combining bulk segregant analysis with HTS has accelerated the identification of causative mutations and has been widely adopted in many research programmes. A major advantage of HTS is the ability to perform bulk segregant analysis after back-crossing to the parental line rather than out-crossing to a polymorphic plant ecotype, which reduces genetic complexity and avoids issues with phenotype penetrance in different ecotypes. Plotting the positions of homozygous polymorphisms in a mutant genome identifies areas of low recombination and is an effective way to detect molecular linkage to a phenotype of interest.

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Current Opinion in Biotechnology: Editing plant genomes with CRISPR/Cas9 (2015)

Current Opinion in Biotechnology: Editing plant genomes with CRISPR/Cas9 (2015) | Publications from The Sainsbury Laboratory | Scoop.it

• Cas9 is an RNA-guided DNA endonuclease innate to prokaryotic immune systems.
• CRISPR/Cas9 has recently emerged as a powerful genome editing tool.
• CRISPR/Cas9 has been successfully applied in many organisms, including model and crop plants.
• CRISPR/Cas9 is a cheap, robust and easy to implement technology.

 

CRISPR/Cas9 is a rapidly developing genome editing technology that has been successfully applied in many organisms, including model and crop plants. Cas9, an RNA-guided DNA endonuclease, can be targeted to specific genomic sequences by engineering a separately encoded guide RNA with which it forms a complex. As only a short RNA sequence must be synthesized to confer recognition of a new target, CRISPR/Cas9 is a relatively cheap and easy to implement technology that has proven to be extremely versatile. Remarkably, in some plant species, homozygous knockout mutants can be produced in a single generation. Together with other sequence-specific nucleases, CRISPR/Cas9 is a game-changing technology that is poised to revolutionise basic research and plant breeding.


Via Kamoun Lab @ TSL
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Front. Plant Sci.: Nonhost resistance to rust pathogens – a continuation of continua (2014)

Front. Plant Sci.: Nonhost resistance to rust pathogens – a continuation of continua (2014) | Publications from The Sainsbury Laboratory | Scoop.it
The Sainsbury Lab's insight:

The rust fungi (order: Pucciniales) are a group of widely distributed fungal plant pathogens, which can infect representatives of all vascular plant groups. Rust diseases significantly impact several crop species and considerable research focuses on understanding the basis of host specificity and nonhost resistance. Like many pathogens, rust fungi vary considerably in the number of hosts they can infect, such as wheat leaf rust (Puccinia triticina), which can only infect species in the genera Triticum and Aegilops, whereas Asian soybean rust (Phakopsora pachyrhizi) is known to infect over 95 species from over 42 genera. A greater understanding of the genetic basis determining host range has the potential to identify sources of durable resistance for agronomically important crops. Delimiting the boundary between host and nonhost has been complicated by the quantitative nature of phenotypes in the transition between these two states. Plant-pathogen interactions in this intermediate state are characterized either by (1) the majority of accessions of a species being resistant to the rust or (2) the rust only being able to partially complete key components of its life cycle. This leads to a continuum of disease phenotypes in the interaction with different plant species, observed as a range from compatibility (host) to complete immunity within a species (nonhost). In this review we will highlight how the quantitative nature of disease resistance in these intermediate interactions is caused by a continuum of defense barriers, which a pathogen needs to overcome for successfully establishing itself in the host. To illustrate continua as this underlying principle, we will discuss the advances that have been made in studying nonhost resistance towards rust pathogens, particularly cereal rust pathogens.

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PLos Pathogens: The Plasmodesmal Protein PDLP1 Localises to Haustoria-Associated Membranes during Downy Mildew Infection and Regulates Callose Deposition (2014)

PLos Pathogens: The Plasmodesmal Protein PDLP1 Localises to Haustoria-Associated Membranes during Downy Mildew Infection and Regulates Callose Deposition (2014) | Publications from The Sainsbury Laboratory | Scoop.it
From molecules to physiology
The Sainsbury Lab's insight:

The downy mildew pathogen Hyaloperonospora arabidopsidis (Hpa) is a filamentous oomycete that invades plant cells via sophisticated but poorly understood structures called haustoria. Haustoria are separated from the host cell cytoplasm and surrounded by an extrahaustorial membrane (EHM) of unknown origin. In some interactions, including Hpa-Arabidopsis, haustoria are progressively encased by host-derived, callose-rich materials but the molecular mechanisms by which callose accumulates around haustoria remain unclear. Here, we report that PLASMODESMATA-LOCATED PROTEIN 1 (PDLP1) is expressed at high levels in Hpainfected cells. Unlike other plasma membrane proteins, which are often excluded from the EHM, PDLP1 is located at the EHM in Hpa-infected cells prior to encasement. The transmembrane domain and cytoplasmic tail of PDLP1 are sufficient to convey this localization. PDLP1 also associates with the developing encasement but this association is lost when encasements are fully mature. We found that the pdlp1,2,3 triple mutant is more susceptible toHpa while overexpression of PDLP1 enhances plant resistance, suggesting that PDLPs enhance basal immunity against Hpa. Haustorial encasements are depleted in callose inpdlp1,2,3 mutant plants whereas PDLP1 over-expression elevates callose deposition around haustoria and across the cell surface. These data indicate that PDLPs contribute to callose encasement of Hpa haustoria and suggests that the deposition of callose at haustoria may involve similar mechanisms to callose deposition at plasmodesmata.

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Bioinformatics: Using 2k + 2 bubble searches to find Single Nucleotide Polymorphisms in k-mer graphs (2014)

Bioinformatics: Using 2k + 2 bubble searches to find Single Nucleotide Polymorphisms in k-mer graphs (2014) | Publications from The Sainsbury Laboratory | Scoop.it
The Sainsbury Lab's insight:

Motivation: Single Nucleotide Polymorphism (SNP) discovery is an important preliminary for understanding genetic variation. With current sequencing methods we can sample genomes comprehensively. SNPs are found by aligning sequence reads against longer assembled references. De Bruijn graphs are efficient data structures that can deal with the vast amount of data from modern technologies. Recent work has shown that the topology of these graphs captures enough information to allow the detection and characterisation of genetic variants, offering an alternative to alignment-based methods. Such methods rely on depth-first walks of the graph to identify closing bifurcations. These methods are conservative or generate many false-positive results, particularly when traversing highly inter-connected (complex) regions of the graph or in regions of very high coverage.

Results: We devised an algorithm that calls SNPs in converted De Bruijn graphs by enumerating 2k + 2 cycles. We evaluated the accuracy of predicted SNPs by comparison with SNP lists from alignment based methods. We tested accuracy of the SNP calling using sequence data from sixteen ecotypes of Arabidopsis thaliana and found that accuracy was high. We found that SNP calling was even across the genome and genomic feature types. Using sequence based attributes of the graph to train a decision tree allowed us to increase accuracy of SNP calls further. Together these results indicate that our algorithm is capable of finding SNPs accurately in complex sub-graphs and potentially comprehensively from whole genome graphs.

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PLOS Pathogens: Expression Profiling during Arabidopsis/Downy Mildew Interaction Reveals a Highly-Expressed Effector That Attenuates Responses to Salicylic Acid (2014)

PLOS Pathogens: Expression Profiling during Arabidopsis/Downy Mildew Interaction Reveals a Highly-Expressed Effector That Attenuates Responses to Salicylic Acid (2014) | Publications from The Sainsbury Laboratory | Scoop.it
From molecules to physiology
The Sainsbury Lab's insight:

Plants have evolved strong innate immunity mechanisms, but successful pathogens evade or suppress plant immunity via effectors delivered into the plant cell. Hyaloperonospora arabidopsidis (Hpa) causes downy mildew on Arabidopsis thaliana, and a genome sequence is available for isolate Emoy2. Here, we exploit the availability of genome sequences for Hpa and Arabidopsis to measure gene-expression changes in both Hpa and Arabidopsis simultaneously during infection. Using a high-throughput cDNA tag sequencing method, we reveal expression patterns of Hpa predicted effectors and Arabidopsis genes in compatible and incompatible interactions, and promoter elements associated with Hpa genes expressed during infection. By resequencing Hpa isolate Waco9, we found it evades Arabidopsis resistance gene RPP1through deletion of the cognate recognized effector ATR1. Arabidopsis salicylic acid (SA)-responsive genes including PR1 were activated not only at early time points in the incompatible interaction but also at late time points in the compatible interaction. By histochemical analysis, we found that Hpa suppresses SA-inducible PR1 expression, specifically in the haustoriated cells into which host-translocated effectors are delivered, but not in non-haustoriated adjacent cells. Finally, we found a highly-expressed Hpa effector candidate that suppresses responsiveness to SA. As this approach can be easily applied to host-pathogen interactions for which both host and pathogen genome sequences are available, this work opens the door towards transcriptome studies in infection biology that should help unravel pathogen infection strategies and the mechanisms by which host defense responses are overcome.

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PNAS: A receptor-like protein mediates the response to pectin modification by activating brassinosteroid signaling (2014)

PNAS: A receptor-like protein mediates the response to pectin modification by activating brassinosteroid signaling (2014) | Publications from The Sainsbury Laboratory | Scoop.it
The Sainsbury Lab's insight:

Plant growth and development depend on the biosynthesis and remodeling of the cell wall. To coordinate these two processes, surveillance mechanisms have evolved to monitor the state of the cell wall. The brassinosteroid (BR) hormone signaling pathway plays an essential role in growth control and regulates the expression of a plethora of cell wall-related genes. We have previously shown that feedback signaling from the wall can modulate the outputs of the BR pathway, ensuring cell wall homeostasis and integrity. Here, we identified a receptor-like protein (RLP44), which mediates the activation of BR signaling through direct interaction with the BR coreceptor BAK1. Thus, RLP44 integrates cell wall surveillance with hormone signaling to control cell wall integrity and growth.

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Plant Physiology: Efficient gene editing in tomato in the first generation using the CRISPR/Cas9 system (2014)

Plant Physiology: Efficient gene editing in tomato in the first generation using the CRISPR/Cas9 system (2014) | Publications from The Sainsbury Laboratory | Scoop.it
The Sainsbury Lab's insight:

The CRISPR/Cas9 system is highly efficient at generating targeted mutations in stable transgenic tomato plants, and homozygous deletions of a desired size can be created in the first generation.

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J Exp Bot: Expression patterns of FLAGELLIN SENSING 2 map to bacterial entry sites in plant shoots and roots (2014)

J Exp Bot: Expression patterns of FLAGELLIN SENSING 2 map to bacterial entry sites in plant shoots and roots (2014) | Publications from The Sainsbury Laboratory | Scoop.it
The Sainsbury Lab's insight:

Pathogens can colonize all plant organs and tissues. To prevent this, each cell must be capable of autonomously triggering defence. Therefore, it is generally assumed that primary sensors of the immune system are constitutively present. One major primary sensor against bacterial infection is the FLAGELLIN SENSING 2 (FLS2) pattern recognition receptor (PRR). To gain insights into its expression pattern, the FLS2 promoter activity in β-glucuronidase (GUS) reporter lines was monitored. The data show that pFLS2::GUS activity is highest in cells and tissues vulnerable to bacterial entry and colonization, such as stomata, hydathodes, and lateral roots. GUS activity is also high in the vasculature and, by monitoring Ca2+responses in the vasculature, it was found that this tissue contributes to flg22-induced Ca2+ burst. The FLS2 promoter is also regulated in a tissue- and cell type-specific manner and is responsive to hormones, damage, and biotic stresses. This results in stimulus-dependent expansion of the FLS2 expression domain. In summary, a tissue- and cell type-specific map of FLS2 expression has been created correlating with prominent entry sites and target tissues of plant bacterial pathogens.

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BMC Genomics: Reference-free SNP detection: dealing with the data deluge (2014)

BMC Genomics: Reference-free SNP detection: dealing with the data deluge (2014) | Publications from The Sainsbury Laboratory | Scoop.it
Reference-free SNP detection, that is identifying SNPs between samples directly from comparison of primary sequencing data with other primary sequencing data and not to a pre-assembled reference genome is an emergent and potentially disruptive technology that is beginning to open up new vistas in variant identification that reveals new applications in non-model organisms and metagenomics. The modern, effcient data structures these tools use enables researchers with a reference sequence to sample many more individuals with lower computing storage and processing overhead. In this article we will discuss the technologies and tools implementing reference-free SNP detection and the potential impact on studies of genetic variation in model and non-model organisms, metagenomics and personal genomics and medicine.
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