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Map: Ash dieback spread across the UK (2012)

Map: Ash dieback spread across the UK (2012) | Plants and Microbes | Scoop.it

AshTag is collating possible sightings by the public of the tree disease. Here are the latest findings, verified by its experts. Submit your sightings via the iPhone app, Android app, or online.

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PLOS Pathogens: Phytomonas : Trypanosomatids Adapted to Plant Environments (2015)

PLOS Pathogens: Phytomonas : Trypanosomatids Adapted to Plant Environments (2015) | Plants and Microbes | Scoop.it

Over 100 years after trypanosomatids were first discovered in plant tissues, Phytomonasparasites have now been isolated across the globe from members of 24 different plant families. Most identified species have not been associated with any plant pathology and to date only two species are definitively known to cause plant disease. These diseases (wilt of palm and coffee phloem necrosis) are problematic in areas of South America where they threaten the economies of developing countries. In contrast to their mammalian infective relatives, our knowledge of the biology of Phytomonas parasites and how they interact with their plant hosts is limited. This review draws together a century of research into plant trypanosomatids, from the first isolations and experimental infections to the recent publication of the first Phytomonas genomes. The availability of genomic data for these plant parasites opens a new avenue for comparative investigations into trypanosomatid biology and provides fresh insight into how this important group of parasites have adapted to survive in a spectrum of hosts from crocodiles to coconuts.

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Farmers Weekly: Cereal disease threat may be worse than in 'horrific' 2014 (2015)

Farmers Weekly: Cereal disease threat may be worse than in 'horrific' 2014 (2015) | Plants and Microbes | Scoop.it

Cereal growers could face a worse disease year this season than the “horrific” 2014 prompted by a mild autumn with plenty of inoculum in fields.


Wheat’s most damaging diseases – septoria and yellow rust (pictured) – are being seen earlier than normal while in barley, mildew, rhynchosporium and net blotch are worse than usual.


Scottish disease expert Fiona Burnett is warning that 2015 could be more serious than 2014 with lots of early-drilled and forward crops picking up disease in the autumn.


“We have forward, thick crops, the right weather and enough inoculum to start the fire,” she tells the Farmers Weekly.

Dr Burnett, crop protection leader at Scotland’s Rural College (SRUC), adds she is seeing more yellow rust and septoria in crops at this stage than for a long time.


Yellow rust crept into East Lothian winter wheat crops by early November, two months ahead of normal, while septoria is being seen in many crops.

“We have only had a little bit of cold weather, what we need is sustained cold weather to kill off disease,” she says.


All the signs are that disease could be worse than in 2014 which she describes as a “horrific disease year” largely due to the mild 2013-14 winter.

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News: Aggressive plant fungus threatens wheat production (2015)

News: Aggressive plant fungus threatens wheat production (2015) | Plants and Microbes | Scoop.it

The spread of exotic and aggressive strains of a plant fungus is presenting a serious threat to wheat production in the UK, according to research published in Genome Biology. The research uses a new surveillance technique that could be applied internationally to respond to the spread of a wide variety of plant diseases.


Wheat is a critical staple and provides 20% of the calories and over 25% of the protein consumed by humans. 'Yellow rust' caused by the fungus Puccinia striiformis f. sp. tritici (PST) is one of the plant's major diseases and is widespread across the major wheat-producing areas of the world. Infections lead to significant reductions in both grain quality and yield, with some rare events leading to the loss of an entire crop. New fungus strains have recently emerged that adapt to warmer temperatures, are more aggressive and have overcome many of the major defensive genes in wheat.


Lead author Diane Saunders of the John Innes Centre and The Genome Analysis Centre (TGAC), UK, said: "Increased virulence, globalization, and climate change, are all increasing the scale and frequency of emerging plant diseases, and threatening global food security.


"Our research shows that in the UK we have a newly emerging population of wheat rust fungus that could be the result of an influx of more exotic and aggressive strains that are displacing the previous population. By continuing to use these new surveillance techniques, not only can we track and respond to the ongoing threat of wheat rust, but our technology opens the door for tracking other plant pathogens, including ash dieback."


Researchers from the John Innes Centre, The Sainsbury Laboratory, TGAC and the National Institute of Agricultural Botany sequenced genetic material from 39 PST-infected samples of wheat collected from 17 UK counties in 2013.


By comparing the fungal RNA with fungal genetic information from previously prevalent populations between 1978 and 2011, they showed that there has been a rapid and dramatic shift in the PST population that could have serious implications for wheat production in the UK.


The 2013 PST samples showed more genetic variation and diversity, reflecting an increase in the evolutionary potential in the UK pathogen population that could enhance their ability to overcome disease resistance in wheat.


Of the samples, 11 were also genetically similar to a PST strain called "Warrior". The strain emerged in 2011 as a serious threat to European wheat production due to its virulence on an array of previously resistant wheat varieties. This indicates that a diverse PST population containing the "Warrior" strain is now prevalent across the UK.


This new diagnostic technique, called "field pathogenomics", could be applied internationally to respond to the spread of a wide variety of plant diseases. By rapidly pinpointing a fungus's genetic make-up from field samples, the technique is able to confirm outbreaks on particular wheat varieties and provides an efficient means of confirming whether previously resistant wheat varieties have been broken by virulent strains of the pathogen. This is in contrast to current techniques which can be lengthy, costly and are only able to sample a relatively small proportion of the fungal population.


The data collection and analysis took just a few months to produce from sample collections from the field, demonstrating the potential for the method to reduce delays and transform current disease surveillance systems. The highly detailed information that is generated could help inform disease incidence predictions and agricultural practices.


Hubbard et al. Genome Biology http://genomebiology.com/2015/16/1/23/abstract

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Current Biology: A Massive Expansion of Effector Genes Underlies Gall-Formation in the Wheat Pest Mayetiola destructor (2015)

Current Biology: A Massive Expansion of Effector Genes Underlies Gall-Formation in the Wheat Pest Mayetiola destructor (2015) | Plants and Microbes | Scoop.it

Gall-forming arthropods are highly specialized herbivores that, in combination with their hosts, produce extended phenotypes with unique morphologies [1]. Many are economically important, and others have improved our understanding of ecology and adaptive radiation [2]. However, the mechanisms that these arthropods use to induce plant galls are poorly understood. We sequenced the genome of the Hessian fly (Mayetiola destructor; Diptera: Cecidomyiidae), a plant parasitic gall midge and a pest of wheat (Triticumspp.), with the aim of identifying genic modifications that contribute to its plant-parasitic lifestyle. Among several adaptive modifications, we discovered an expansive reservoir of potential effector proteins. Nearly 5% of the 20,163 predicted gene models matched putative effector gene transcripts present in the M. destructor larval salivary gland. Another 466 putative effectors were discovered among the genes that have no sequence similarities in other organisms. The largest known arthropod gene family (family SSGP-71) was also discovered within the effector reservoir. SSGP-71 proteins lack sequence homologies to other proteins, but their structures resemble both ubiquitin E3 ligases in plants and E3-ligase-mimicking effectors in plant pathogenic bacteria. SSGP-71 proteins and wheat Skp proteins interact in vivo. Mutations in different SSGP-71 genes avoid the effector-triggered immunity that is directed by the wheat resistance genes H6 and H9. Results point to effectors as the agents responsible for arthropod-induced plant gall formation.

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Summer School "PLANT MICROBE INTERACTIONS" @ The Sainsbury Laboratory, 17-28 August 2015, Norwich, UK

Summer School "PLANT MICROBE INTERACTIONS" @ The Sainsbury Laboratory, 17-28 August 2015, Norwich, UK | Plants and Microbes | Scoop.it
The last 20 years have provided a sophisticated understanding of how plants recognise relatively conserved microbial patterns to activate defence. In recent years DNA sequencing allowed genomes and transcriptomes of eukaryotic rusts and mildew pathogens to be studied and high-throughput imaging permit the study and visualisation of intracellular interactions during pathogenesis and defence.


We will present many aspects of plant- microbe interactions including:

- gene discovery
- genome analysis
- intra-cellular interactions with high-throughput imaging technology
- mechanistic understanding of cellular and molecular processes to translational activities


The focus on the dynamic and interactive practical sessions will naturally promote strong interactions between lecturers and participants.

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Jean-Michel Ané's curator insight, February 25, 11:53 AM

That seems an awesome Summer School.

BTW... I want the same chair as Dan MacLean :-)

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Frontiers in Plant Science: The “sensor domains” of plant NLR proteins: more than decoys? (2015)

Frontiers in Plant Science: The “sensor domains” of plant NLR proteins: more than decoys? (2015) | Plants and Microbes | Scoop.it

Our conceptual and mechanistic understanding of how plant nucleotide-binding leucine-rich repeat (NLR or NB-LRR) proteins perceive pathogens continues to advance. NLRs are intracellular multidomain proteins that recognize pathogen-derived effectors either directly or indirectly (Jones and Dangl, 2006; van der Hoorn and Kamoun, 2008; Dodds and Rathjen, 2010; Cesari et al., 2014). In the direct model, the NLR protein binds a pathogen effector or serves as a substrate for the effector’s enzymatic activity. In the indirect model, the NLR recognizes modifications of additional host protein(s) targeted by the effector. Such intermediate host protein(s) are often called effector targets (ETs). However, given that effectors can act on multiple host targets, the specific protein that mediates recognition by the NLR may not be the effector’s operative target and may have evolved to function as a decoy dedicated to pathogen detection. This “decoy” model contrasts with the “guard” model in which the NLR perceives the effector via its action on its operative target (van der Hoorn and Kamoun, 2008). 

In a recent article, Cesari et al. (2014) elegantly synthesized the literature to propose a novel model of how NLRs recognise effectors termed the “integrated decoy” hypothesis. Based on new data from several pathosystems, it appears that some NLRs recognize pathogen effectors through extraneous domains that have evolved by duplication of an ET followed by fusion into the NLR. This NLR-integrated domain mimics the effector binding/substrate property of the original ET to enable pathogen detection. In addition, these “receptor” or “sensor” NLRs typically partner with NLR proteins with a classic architecture that function as signalling partners required for the resistance response (Eitas and Dangl, 2010; Cesari et al., 2013; Cesari et al., 2014; Williams et al., 2014).

Here, we expand on the Cesari et al. (2014) model and introduce the possibility that NLR-integrated domains do not have to be decoys (as in defective mimics) of the effector’s operative target. Indeed, in addition to binding effectors or serving as their substrates, operative targets carry a biochemical activity that is modulated by the effector. The perturbation of this activity by the effector leads to effector-triggered susceptibility, an activity often related to immunity (Boller and He, 2009; Dodds and Rathjen, 2010; Win et al., 2012). Clearly NLR-integrated domains must retain the “sensor” activity of the ancestral ET, but they could also retain their biochemical activity, continuing to function in the effector-targeted pathway even as an extraneous domain within a classic NLR architecture. At present, this possibility cannot be discounted given that the biochemical activities of the ancestral ETs and their NLR-integrated counterparts are generally unknown. Additionally, when NLR-fusions occurred recently, there may not have been enough time for the integrated ET to lose its original function and evolve into a decoy. We therefore propose to refer to the extraneous domains of classic NLR proteins described by Cesari et al. (2014) as sensor domains (SD), a term that is agnostic to any potential biochemical activities of the integrated module.

How to test whether or not SDs are decoys? We propose a straightforward genetic test that can reject the decoy hypothesis. Isogenic plants either carrying or lacking the NLR-SD can be challenged with a pathogen strain that lacks the matching avirulence effector (Figure 1). There are several possible outcomes. If the NLR-SD isogenic lines do not differ in their response to the pathogen without the matching effector, the result is inconclusive and the null decoy hypothesis cannot be rejected. If the presence of NLR-SD without the known matching effector shows higher levels of resistance, and there are no signs of typical effector-triggered immunity, then the SD is likely to have retained the ET biochemical activity and contributes to basal immunity in a manner analogous to the ancestral ET. An even more interesting result would be if in the absence of the matching effector, the NLR-SD line is more susceptible as has been shown for several ETs (van Schie and Takken, 2014). In this scenario, another (unrecognized) effector might still be targeting the original biochemical activity of the SD domain. It would be conceptually fascinating if an NLR that functions as a resistance (R) gene against certain strains of a pathogen becomes a susceptibility (S) gene when exposed to other strains. Once again, this concept emphasizes how the outcome of plant-pathogen interactions is so critically dependent on the genotypes of the interacting organisms – a gene that has a certain impact in a particular genetic combination can have the exact opposite effect in another (Jones and Dangl, 2006; van der Hoorn and Kamoun, 2008; Dodds and Rathjen, 2010; Win et al., 2012).

Our goal is not to engage in an exercise in semantics. However, we wish to avoid conceptually restrictive terminology and urge the plant-microbe interactions community to test a rich spectrum of models and hypotheses. The proposed sensor domain terminology would accommodate this breadth of ideas. Ultimately, it may very well turn out that the majority, if not all, of the NLR integrated domains have lost their biochemical activities and have evolved into decoys. Also, it is possible that the sensor domain has already evolved into a decoy prior to recombination into a NLR. Nonetheless, further genetic and biochemical experiments are required to determine whether sensor domains of NLR-SDs are decoys or biochemically functional duplicates of their ancestral ETs.

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5th Xanthomonas Genomics Conference, July 8 - 11, 2015, Bogotá, Colombia

5th Xanthomonas Genomics Conference, July 8 - 11, 2015, Bogotá, Colombia | Plants and Microbes | Scoop.it
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PLOS Pathogens: Recognition and Activation Domains Contribute to Allele-Specific Responses of an Arabidopsis NLR Receptor to an Oomycete Effector Protein (2015)

PLOS Pathogens: Recognition and Activation Domains Contribute to Allele-Specific Responses of an Arabidopsis NLR Receptor to an Oomycete Effector Protein (2015) | Plants and Microbes | Scoop.it

In plants, specific recognition of pathogen effector proteins by nucleotide-binding leucine-rich repeat (NLR) receptors leads to activation of immune responses. RPP1, an NLR from Arabidopsis thaliana, recognizes the effector ATR1, from the oomycete pathogen Hyaloperonospora arabidopsidis, by direct association via C-terminal leucine-rich repeats (LRRs). Two RPP1 alleles, RPP1-NdA and RPP1-WsB, have narrow and broad recognition spectra, respectively, with RPP1-NdA recognizing a subset of the ATR1 variants recognized by RPP1-WsB. In this work, we further characterized direct effector recognition through random mutagenesis of an unrecognized ATR1 allele, ATR1-Cala2, screening for gain-of-recognition phenotypes in a tobacco hypersensitive response assay. We identified ATR1 mutants that a) confirm surface-exposed residues contribute to recognition by RPP1, and b) are recognized by and activate the narrow-spectrum allele RPP1-NdA, but not RPP1-WsB, in co-immunoprecipitation and bacterial growth inhibition assays. Thus, RPP1 alleles have distinct recognition specificities, rather than simply different sensitivity to activation. Using chimeric RPP1 constructs, we showed that RPP1-NdA LRRs were sufficient for allele-specific recognition (association with ATR1), but insufficient for receptor activation in the form of HR. Additional inclusion of the RPP1-NdA ARC2 subdomain, from the central NB-ARC domain, was required for a full range of activation specificity. Thus, cooperation between recognition and activation domains seems to be essential for NLR function.

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David Kuykendall's curator insight, February 15, 12:54 PM

This is an example of cutting-edge model plant Arabidopsis pathogenesis/resistance research.

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New Phytologist: How harmonious are arbuscular mycorrhizal symbioses? Inconsistent concepts reflect different mindsets as well as results (2014)

New Phytologist: How harmonious are arbuscular mycorrhizal symbioses? Inconsistent concepts reflect different mindsets as well as results (2014) | Plants and Microbes | Scoop.it

Arbuscular mycorrhizal (AM) symbioses involve transfer of soil nutrients to plants and plant-derived organic compounds to AM fungi. Many experiments have shown that individual symbioses are ‘mutualistic’ (Table 1). However, outcomes in relation to the nonmycorrhizal (NM) state are not always positive for plants, although they are for all AM fungi, which are obligate symbionts. Different AM fungi produce different growth-related responses in individual plants and there are large differences in responsiveness among different plant taxa in relation to colonization by the same AM fungal taxon (Klironomos, 2003). Neutral outcomes for the plant may be termed ‘commensal’, and negative ones ‘parasitic’ (Table 1). Outcomes are influenced by many abiotic and biotic factors (Johnson et al., 1997).


Image from Parniske (2008) http://www.nature.com/nrmicro/journal/v6/n10/full/nrmicro1987.html

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New Phytologist: The fungal core effector Pep1 is conserved across smuts of dicots and monocots (2015)

New Phytologist: The fungal core effector Pep1 is conserved across smuts of dicots and monocots (2015) | Plants and Microbes | Scoop.it
  • The secreted fungal effector Pep1 is essential for penetration of the host epidermis and establishment of biotrophy in the Ustilago maydis–maize pathosystem. Previously, Pep1 was found to be an inhibitor of apoplastic plant peroxidases, which suppresses the oxidative burst, a primary immune response of the host plant and enables fungal colonization.
  • To investigate the conservation of Pep1 in other pathogens, genomes of related smut species were screened for pep1 orthologues. Pep1 proteins were produced in Escherichia coli for functional assays. The biological function of Pep1 was tested by heterologous expression in U. maydis and Hordeum vulgare.
  • Pep1 orthologues revealed a remarkable degree of sequence conservation, indicating that this effector might play a fundamental role in virulence of biotrophic smut fungi. Pep1 function and its role in virulence are conserved in different pathogenic fungi, even across the monocot–dicot border of host plants.
  • The findings described in this study classify Pep1 as a phylogenetically conserved fungal core effector. Furthermore, we documented the influence of Pep1 on the disease caused by Blumeria graminis f. sp. hordei which is a non-smut-related pathosystem.
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Frontiers: Strategies for transferring resistance into wheat: from wide crosses to GM cassettes (2014)

Frontiers: Strategies for transferring resistance into wheat: from wide crosses to GM cassettes (2014) | Plants and Microbes | 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 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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The Sainsbury Lab's curator insight, December 8, 2014 5:30 AM

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.

Bharat Employment's curator insight, January 20, 11:42 PM

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Mol Plant Pathol: A Meloidogyne incognita effector is imported into the nucleus and exhibits transcriptional activation activity in planta (2014)

Mol Plant Pathol: A Meloidogyne incognita effector is imported into the nucleus and exhibits transcriptional activation activity in planta (2014) | Plants and Microbes | Scoop.it

Root-knot nematodes are sedentary biotrophic endoparasites that maintain a complex interaction with their host plants. Nematode effector proteins are synthesized in the oesophageal glands of nematodes and secreted into plant tissue through a needle-like stylet. Effectors characterized to date have been shown to mediate processes essential for nematode pathogenesis. To gain an insight into their site of action and putative function, the subcellular localization of 13 previously isolated Meloidogyne incognita effectors was determined. Translational fusions were created between effectors and EGFP-GUS (enhanced green fluorescent protein-β-glucuronidase) reporter genes, which were transiently expressed in tobacco leaf cells. The majority of effectors localized to the cytoplasm, with one effector, 7H08, imported into the nuclei of plant cells. Deletion analysis revealed that the nuclear localization of 7H08 was mediated by two novel independent nuclear localization domains. As a result of the nuclear localization of the effector, 7H08 was tested for the ability to activate gene transcription. 7H08 was found to activate the expression of reporter genes in both yeast and plant systems. This is the first report of a plant-parasitic nematode effector with transcriptional activation activity.

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SEB Prague 2015: Plant Biology Sessions, June 30-July 3

SEB Prague 2015: Plant Biology Sessions, June 30-July 3 | Plants and Microbes | Scoop.it

In nature plants are colonised by beneficial and pathogenic microbes. While plants benefit from the interactions with beneficial microbes (mutualists), pathogenic microbes cause diseases and arrest plant growth. Both mutualistic and pathogenic microbes are initially confronted with a highly effective immune system, which they have to overcome in order to colonise their hosts. Hence, despite the different outcomes of mutualistic and pathogenic interactions, both microbial groups face the same hurdles to establish their accommodation in the plant. A plethora of recent studies indicated that mutualists and pathogens secrete effectors, mainly proteins but also small interfering RNAs, with the purpose not only to manipulate host immunity but also to modify host metabolism in order to create an environment suitable for microbial reproduction.


The session will highlight the current knowledge of how mutualistic and pathogenic microbes employ effectors to successfully establish their respective interactions with plants. The aim is to bring together a group of experts in plant microbe interactions to identify commonalities and discrepancies in the mode of action of mutualistic and pathogenic effectors. Improving our understanding of effector biology will enable us to uncover the molecular principles governing mutualism and disease outbreaks and to synergistically apply this knowledge to sustainably enhance stress adaptation in crops.

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MBPP2015 | 2015 Molecular Biology of Plant Pathogens Conference at the University of the West of England, Bristol on 8-9 April 2015

MBPP2015 | 2015 Molecular Biology of Plant Pathogens Conference at the University of the West of England, Bristol on 8-9 April 2015 | Plants and Microbes | Scoop.it

The 2015 Molecular Biology of Plant Pathogens (MBPP) conference will be held at the University of the West of England (UWE), Bristol on the 8th-9th April 2015. This will be the 23rd MBPP conference!


UWE is the largest university in the South West of England with over 30,000 students and approximately 3,500 staff. UWE has a long and interesting history starting life as a Merchant Venturer’s Navigation College in 1595 and undergoing many changes before gaining University status in 1992. Today UWE attracts students from all over the UK as well as a significant number of international students from 140 countries worldwide.


UWE has an active research community which makes a significant contribution to advances in industry, commerce, health and technology both nationally and internationally. The organisers of this years’ MBPP conference, Professor Dawn Arnold, Dr Carrie Brady and Dr Helen Neale work within the Centre for Research in Bioscience (CRIB) which leads world-class research in areas of strategic importance including plant science, agri-food, bio-sensing and biomedicine.


MBPP provides an excellent forum for networking between junior and senior scientists. The primary focus is on providing PhD students and post-doctoral scientists the opportunity to give oral presentations in front of a wide range of national and international researchers.


There will also be three keynote talks by internationally renowned scientists Professor Pietro Spanu (Imperial College), Dr Chris Ridout (John Innes Centre) and Professor Teresa Coutinho (Forestry and Agricultural Biotechnology Institute, University of Pretoria, South Africa). Please see our biographies tab for more information on these speakers.

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PLOS Pathogens: Molecular and Functional Analyses of a Maize Autoactive NB-LRR Protein Identify Precise Structural Requirements for Activity (2015)

PLOS Pathogens: Molecular and Functional Analyses of a Maize Autoactive NB-LRR Protein Identify Precise Structural Requirements for Activity (2015) | Plants and Microbes | Scoop.it

Plant disease resistance is often mediated by nucleotide binding-leucine rich repeat (NLR) proteins which remain auto-inhibited until recognition of specific pathogen-derived molecules causes their activation, triggering a rapid, localized cell death called a hypersensitive response (HR). Three domains are recognized in one of the major classes of NLR proteins: a coiled-coil (CC), a nucleotide binding (NB-ARC) and a leucine rich repeat (LRR) domains. The maize NLR gene Rp1-D21 derives from an intergenic recombination event between two NLR genes, Rp1-D and Rp1-dp2 and confers an autoactive HR. We report systematic structural and functional analyses of Rp1 proteins in maize and Nbenthamiana to characterize the molecular mechanism of NLR activation/auto-inhibition. We derive a model comprising the following three main features: Rp1 proteins appear to self-associate to become competent for activity. The CC domain is signaling-competent and is sufficient to induce HR. This can be suppressed by the NB-ARC domain through direct interaction. In autoactive proteins, the interaction of the LRR domain with the NB-ARC domain causes de-repression and thus disrupts the inhibition of HR. Further, we identify specific amino acids and combinations thereof that are important for the auto-inhibition/activity of Rp1 proteins. We also provide evidence for the function of MHD2, a previously uncharacterized, though widely conserved NLR motif. This work reports several novel insights into the precise structural requirement for NLR function and informs efforts towards utilizing these proteins for engineering disease resistance.

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New Phytologist: Comparative genomics identifies the Magnaporthe oryzae avirulence effector AvrPi9 that triggers Pi9-mediated blast resistance in rice (2015)

New Phytologist: Comparative genomics identifies the Magnaporthe oryzae avirulence effector AvrPi9 that triggers Pi9-mediated blast resistance in rice (2015) | Plants and Microbes | Scoop.it
  • We identified the Magnaporthe oryzae avirulence effector AvrPi9 cognate to rice blast resistance gene Pi9 by comparative genomics of requisite strains derived from a sequential planting method.
  • AvrPi9 encodes a small secreted protein that appears to localize in the biotrophic interfacial complex and is translocated to the host cell during rice infection. AvrPi9 forms a tandem gene array with its paralogue proximal to centromeric region of chromosome 7. AvrPi9 is expressed highly at early stages during initiation of blast disease.
  • Virulent isolate strains contain Mg-SINE within the AvrPi9 coding sequence. Loss of AvrPi9 did not lead to any discernible defects during growth or pathogenesis in M. oryzae. This study reiterates the role of diverse transposable elements as off-switch agents in acquisition of gain-of-virulence in the rice blast fungus.
  • The prevalence of AvrPi9 correlates well with the avirulence pathotype in diverse blast isolates from the Philippines and China, thus supporting the broad-spectrum resistance conferred by Pi9 in different rice growing areas. Our results revealed that Pi9 and Piz-t at the Pi2/9 locus activate race specific resistance by recognizing sequence-unrelated AvrPi9 and AvrPiz-t genes, respectively.
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Current Opinion in Insect Science: Disruption of insect transmission of plant viruses (2015)

Current Opinion in Insect Science: Disruption of insect transmission of plant viruses (2015) | Plants and Microbes | Scoop.it

Plant-infecting viruses are transmitted by a diverse array of organisms including insects, mites, nematodes, fungi, and plasmodiophorids. Virus interactions with these vectors are diverse, but there are some commonalities. Generally the infection cycle begins with the vector encountering the virus in the plant and the virus is acquired by the vector. The virus must then persist in or on the vector long enough for the virus to be transported to a new host and delivered into the plant cell. Plant viruses rely on their vectors for breaching the plant cell wall to be delivered directly into the cytosol. In most cases, viral capsid or membrane glycoproteins are the specific viral proteins that are required for transmission and determinants of vector specificity. Specific molecules in vectors also interact with the virus and while there are few-identified to no-identified receptors, candidate recognition molecules are being further explored in these systems. Due to the specificity of virus transmission by vectors, there are defined steps that represent good targets for interdiction strategies to disrupt the disease cycle. This review focuses on new technologies that aim to disrupt the virus–vector interaction and focuses on a few of the well-characterized virus–vector interactions in the field. In closing, we discuss the importance of integration of these technologies with current methods for plant virus disease control.

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Steve Marek's curator insight, February 26, 9:27 AM

Not fungal, but still an excellent review with great insights on important plant pathosystems.

Bharat Employment's curator insight, February 27, 4:46 AM

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Nature: NIK1-mediated translation suppression functions as a plant antiviral immunity mechanism (2015)

Nature: NIK1-mediated translation suppression functions as a plant antiviral immunity mechanism (2015) | Plants and Microbes | Scoop.it

Plants and plant pathogens are subject to continuous co-evolutionary pressure for dominance, and the outcomes of these interactions can substantially impact agriculture and food security123. In virus–plant interactions, one of the major mechanisms for plant antiviral immunity relies on RNA silencing, which is often suppressed by co-evolving virus suppressors, thus enhancing viral pathogenicity in susceptible hosts1. In addition, plants use the nucleotide-binding and leucine-rich repeat (NB-LRR) domain-containing resistance proteins, which recognize viral effectors to activate effector-triggered immunity in a defence mechanism similar to that employed in non-viral infections23. Unlike most eukaryotic organisms, plants are not known to activate mechanisms of host global translation suppression to fight viruses12. Here we demonstrate in Arabidopsis that the constitutive activation of NIK1, a leucine-rich repeat receptor-like kinase (LRR-RLK) identified as a virulence target of the begomovirus nuclear shuttle protein (NSP)456, leads to global translation suppression and translocation of the downstream component RPL10 to the nucleus, where it interacts with a newly identified MYB-like protein, L10-INTERACTING MYB DOMAIN-CONTAINING PROTEIN (LIMYB), to downregulate translational machinery genes fully. LIMYB overexpression represses ribosomal protein genes at the transcriptional level, resulting in protein synthesis inhibition, decreased viral messenger RNA association with polysome fractions and enhanced tolerance to begomovirus. By contrast, the loss of LIMYBfunction releases the repression of translation-related genes and increases susceptibility to virus infection. Therefore, LIMYB links immune receptor LRR-RLK activation to global translation suppression as an antiviral immunity strategy in plants.

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bioRxiv: The NLR helper protein NRC3 but not NRC1 is required for Pto-mediated cell death in Nicotiana benthamiana (2015)

bioRxiv: The NLR helper protein NRC3 but not NRC1 is required for Pto-mediated cell death in Nicotiana benthamiana (2015) | Plants and Microbes | Scoop.it

Intracellular immune receptors of the nucleotide-binding leucine-rich repeat (NB-LRR or NLR) proteins often function in pairs, with "helper" proteins required for the activity of "sensors" that mediate pathogen recognition. The NLR helper NRC1 (NB-LRR protein required for HR-associated cell death 1) has been described as a signalling hub required for the cell death mediated by both cell surface and intracellular immune receptors in the model plant Nicotiana benthamiana. However, this work predates the availability of the N. benthamiana genome and whether NRC1 is indeed required for the reported phenotypes has not been confirmed. Here, we investigated the NRC family of solanaceous plants using a combination of genome annotation, phylogenetics, gene silencing and genetic complementation experiments. We discovered that a paralog of NRC1, we termed NRC3, is required for the hypersensitive cell death triggered by the disease resistance protein Pto but not Rx and Mi-1.2. NRC3 may also contribute to the hypersensitive cell death triggered by the receptor-like protein Cf-4. Our results highlight the importance of applying genetic complementation to validate gene function in RNA silencing experiments.

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PLOS Pathogens: The RhoGAP SPIN6 Associates with SPL11 and OsRac1 and Negatively Regulates Programmed Cell Death and Innate Immunity in Rice (2015)

PLOS Pathogens: The RhoGAP SPIN6 Associates with SPL11 and OsRac1 and Negatively Regulates Programmed Cell Death and Innate Immunity in Rice (2015) | Plants and Microbes | Scoop.it

The ubiquitin proteasome system in plants plays important roles in plant-microbe interactions and in immune responses to pathogens. We previously demonstrated that the rice U-box E3 ligase SPL11 and its Arabidopsis ortholog PUB13 negatively regulate programmed cell death (PCD) and defense response. However, the components involved in the SPL11/PUB13-mediated PCD and immune signaling pathway remain unknown. In this study, we report that SPL11-interacting Protein 6 (SPIN6) is a Rho GTPase-activating protein (RhoGAP) that interacts with SPL11 in vitro and in vivo. SPL11 ubiquitinates SPIN6 in vitro and degrades SPIN6 in vivo via the 26S proteasome-dependent pathway. Both RNAi silencing in transgenic rice and knockout of Spin6 in a T-DNA insertion mutant lead to PCD and increased resistance to the rice blast pathogen Magnaporthe oryzae and the bacterial blight pathogen Xanthomonas oryzae pv. oryzae. The levels of reactive oxygen species and defense-related gene expression are significantly elevated in both the Spin6 RNAi and mutant plants. Strikingly, SPIN6 interacts with the small GTPase OsRac1, catalyze the GTP-bound OsRac1 into the GDP-bound state in vitro and has GAP activity towards OsRac1 in rice cells. Together, our results demonstrate that the RhoGAP SPIN6 acts as a linkage between a U-box E3 ligase-mediated ubiquitination pathway and a small GTPase-associated defensome system for plant immunity.

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Plant Cell: Recruitment of PLANT U-BOX13 and the PI4Kβ1/β2 Phosphatidylinositol-4 Kinases by the Small GTPase RabA4B Plays Important Roles during Salicylic Acid-Mediated Plant Defense Signaling in ...

Plant Cell: Recruitment of PLANT U-BOX13 and the PI4Kβ1/β2 Phosphatidylinositol-4 Kinases by the Small GTPase RabA4B Plays Important Roles during Salicylic Acid-Mediated Plant Defense Signaling in ... | Plants and Microbes | Scoop.it

Protection against microbial pathogens involves the activation of cellular immune responses in eukaryotes, and this cellular immunity likely involves changes in subcellular membrane trafficking. In eukaryotes, members of the Rab GTPase family of small monomeric regulatory GTPases play prominent roles in the regulation of membrane trafficking. We previously showed that RabA4B is recruited to vesicles that emerge from trans-Golgi network (TGN) compartments and regulates polarized membrane trafficking in plant cells. As part of this regulation, RabA4B recruits the closely related phosphatidylinositol 4-kinase (PI4K) PI4Kβ1 and PI4Kβ2 lipid kinases. Here, we identify a second Arabidopsis thaliana RabA4B-interacting protein, PLANT U-BOX13 (PUB13), which has recently been identified to play important roles in salicylic acid (SA)-mediated defense signaling. We show that PUB13 interacts with RabA4B through N-terminal domains and with phosphatidylinositol 4-phosphate (PI-4P) through a C-terminal armadillo domain. Furthermore, we demonstrate that a functional fluorescent PUB13 fusion protein (YFP-PUB13) localizes to TGN and Golgi compartments and that PUB13, PI4Kβ1, and PI4Kβ2 are negative regulators of SA-mediated induction of pathogenesis-related gene expression. Taken together, these results highlight a role for RabA4B and PI-4P in SA-dependent defense responses.

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Cellular Microbiology: Perturbation of host ubiquitin systems by plant pathogen/pest effector proteins (2015)

Cellular Microbiology: Perturbation of host ubiquitin systems by plant pathogen/pest effector proteins (2015) | Plants and Microbes | Scoop.it

Microbial pathogens and pests of animals and plants secrete effector proteins into host cells, altering cellular physiology to the benefit of the invading parasite. Research in the past decade has delivered significant new insights into the molecular mechanisms of how these effector proteins function, with a particular focus on modulation of host immunity-related pathways. One host system that has emerged as a common target of effectors is the ubiquitination system in which substrate proteins are post-translationally modified by covalent conjugation with the small protein ubiquitin. This modification, typically via isopeptide bond formation through a lysine side chain of ubiquitin, can result in target degradation, relocalization, altered activity or affect protein–protein interactions. In this review, I focus primarily on how effector proteins from bacterial and filamentous pathogens of plants and pests perturb host ubiquitination pathways that ultimately include the 26S proteasome. The activities of these effectors, in how they affect ubiquitin pathways in plants, reveal how pathogens have evolved to identify and exploit weaknesses in this system that deliver increased pathogen fitness.

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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) | Plants and Microbes | 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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MPMI: 14-3-3 proteins in plant-pathogen interactions (2015)

MPMI: 14-3-3 proteins in plant-pathogen interactions (2015) | Plants and Microbes | Scoop.it

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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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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New Phytologist: Fungal associations of basal vascular plants: reopening a closed book? (2014)

New Phytologist: Fungal associations of basal vascular plants: reopening a closed book? (2014) | Plants and Microbes | Scoop.it

The widely held hypothesis that Glomeromycota fungi alone formed the ancestral land plant–fungus symbiosis (Pirozynski & Dalpé, 1989; Selosse & Le Tacon, 1998; Wang & Qiu, 2006; Parniske, 2008) has recently been challenged by new lines of evidence from molecular, cytological, functional and palaeontological studies. First, liverworts of the earliest divergent clade, the Haplomitriopsida, form a mutualistic mycorrhiza-like relationship, whereby there is reciprocal exchange of plant carbon (C) for fungal nitrogen (N) and phosphorus (P), with members of the Mucoromycotina (Bidartondo et al., 2011; Field et al., 2014), a fungal lineage considered basal or sister to the Glomeromycota (James et al., 2006; Lin et al., 2014). Secondly, other basal plants, including complex and simple thalloid liverworts and hornworts, enter into associations with both Mucoromycotina and Glomeromycota fungi, sometimes simultaneously (Bidartondo et al., 2011; Desirò et al., 2013). Thirdly, dual partnerships involving fungi with affinities to Glomeromycota and Mucoromycotina have been reported in fossils of early vascular plants from the Devonian (Strullu-Derrien et al., 2014).


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