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Mississippi Crop Situation: Wheat Disease Update: March 30, 2013

Mississippi Crop Situation: Wheat Disease Update: March 30, 2013 | Plants and Microbes | Scoop.it

Stripe rust - Stripe rust continues to be observed throughout Mississippi as well as Louisiana and Arkansas.  At this time I would not say the disease is widespread (at least in MS) but symptoms can clearly be observed in some fields throughout the MS Delta.

 

Leaf rust - Over the past week leaf rust has been observed in a few Delta wheat fields.  Leaf rust differs from stripe rust in that pustules are more scattered, appear larger in size, and sporulation from the pustule will be more orange in color (see attached photo for comparison between leaf and stripe rust).  As a plant pathologist I am not near as concerned about leaf rust as I am stripe rust.  A similar situation could be stated regarding common rust in corn as compared to southern rust in corn. 

 

Powdery mildew - Powdery mildew can still be observed in some wheat fields in southern MS.  In addition, powdery mildew has been detected in the south Delta.  More than likely, those fields with observable powdery mildew were exposed to prolonged wet, cool conditions.  Scout fields for powdery mildew and keep in mind that in some instances “hot spots” of powdery mildew can be visible from the turn row but can easily be confused with stripe rust, nutrient deficiencies, freeze injury, and herbicide drift/injury. Part the canopy back to observe for powdery mildew.  Even though the disease may be present lower in the plant canopy remember that yield loss is dictated by disease being present on the flag leaf.  If the flag leaf has emerged and it looks like the disease is going to remain in the lower canopy I don’t suggest you apply a fungicide.

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Eastern Daily Press: Dr Dolittle may have talked to the animals, but Norwich scientists are more interested in what our plants have to say (April 1, 2013)

Eastern Daily Press: Dr Dolittle may have talked to the animals, but Norwich scientists are more interested in what our plants have to say (April 1, 2013) | Plants and Microbes | Scoop.it

It’s bad news for vegetarians as researchers reveal that plants really do have feelings after registering plants ‘sighing’ in their laboratories.

 

Researchers at the Fuldstændig Består University in Denmark claim that research carried out under laboratory conditions proves plants have feelings and can react to external stimuli in “an almost human” fashion. And at the John Innes Centre in Norwich, work will soon begin on developing a communication system which will allow scientists to hold ‘conversations’ with plants. “Much of our work is carried out in a warehouse-sized glasshouse where a huge number of genetically-modified plants are kept so we can carry out experiments which help us advise farmers how to increase their efficiency,” said Danish plant researcher Dr Aleksander Eksisterer-Ikke. “We noticed that after a few weeks, there would be an audible ‘sigh’ from the plants before we began our experimentation. It was quite marked. When we investigated more thoroughly, we realised that the plants were reacting to our presence and the likelihood of undergoing experimentation. “We then concentrated our research on the emotional responses of the plants to various stimuli such as loud music, shouting and soothing words and discovered that the plants would display an almost human reaction. “One of our discoveries was that the plants hated listening to Bon Jovi and Bryan Adams but enjoyed being read The Hungry Caterpillar, especially the bit where the caterpillar turns into a butterfly. Using specialist equipment, we registered what sounded almost like a cheer.”

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Twitter / @HuffingtonPost: Could coffee plant disease turn Americans into tea drinkers? (2013)

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PLOS ONE: Identification and Characterisation CRN Effectors in Phytophthora capsici Shows Modularity and Functional Diversity (2013)

PLOS ONE: Identification and Characterisation CRN Effectors in Phytophthora capsici Shows Modularity and Functional Diversity (2013) | Plants and Microbes | Scoop.it

Phytophthora species secrete a large array of effectors during infection of their host plants. The Crinkler (CRN) gene family encodes a ubiquitous but understudied class of effectors with possible but as of yet unknown roles in infection. To appreciate CRN effector function inPhytophthora, we devised a simple Crn gene identification and annotation pipeline to improve effector prediction rates. We predicted 84 full-length CRN coding genes and assessed CRN effector domain diversity in sequenced Oomycete genomes. These analyses revealed evidence of CRN domain innovation in Phytophthora and expansion in the Peronosporales. We performed gene expression analyses to validate and define two classes of CRN effectors, each possibly contributing to infection at different stages. CRN localisation studies revealed that P. capsici CRN effector domains target the nucleus and accumulate in specific sub-nuclear compartments. Phenotypic analyses showed that few CRN domains induce necrosis when expressed in planta and that one cell death inducing effector, enhances P. capsicivirulence on Nicotiana benthamiana. These results suggest that the CRN protein family form an important class of intracellular effectors that target the host nucleus during infection. These results combined with domain expansion in hemi-biotrophic and necrotrophic pathogens, suggests specific contributions to pathogen lifestyles. This work will bolster CRN identification efforts in other sequenced oomycete species and set the stage for future functional studies towards understanding CRN effector functions.

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PLOS Pathogens: Trehalose Biosynthesis Promotes Pseudomonas aeruginosa Pathogenicity in Plants (2013)

PLOS Pathogens: Trehalose Biosynthesis Promotes Pseudomonas aeruginosa Pathogenicity in Plants (2013) | Plants and Microbes | Scoop.it

Pseudomonas aeruginosa strain PA14 is a multi-host pathogen that infects plants, nematodes, insects, and vertebrates. Many PA14 factors are required for virulence in more than one of these hosts. Noting that plants have a fundamentally different cellular architecture from animals, we sought to identify PA14 factors that are specifically required for plant pathogenesis. We show that synthesis by PA14 of the disaccharide trehalose is required for pathogenesis in Arabidopsis, but not in nematodes, insects, or mice. In-frame deletion of two closely-linked predicted trehalose biosynthetic operons, treYZ and treS, decreased growth in Arabidopsis leaves about 50 fold. Exogenously co-inoculated trehalose, ammonium, or nitrate, but not glucose, sulfate, or phosphate suppressed the phenotype of the double ΔtreYZΔtreSmutant. Exogenous trehalose or ammonium nitrate does not suppress the growth defect of the double ΔtreYZΔtreS mutant by suppressing the plant defense response. Trehalose also does not function intracellularly in P. aeruginosa to ameliorate a variety of stresses, but most likely functions extracellularly, because wild-type PA14 rescued the in vivo growth defect of the ΔtreYZΔtreS in trans. Surprisingly, the growth defect of the double ΔtreYZΔtreS double mutant was suppressed by various Arabidopsis cell wall mutants that affect xyloglucan synthesis, including an xxt1xxt2 double mutant that completely lacks xyloglucan, even though xyloglucan mutants are not more susceptible to pathogens and respond like wild-type plants to immune elicitors. An explanation of our data is that trehalose functions to promote the acquisition of nitrogen-containing nutrients in a process that involves the xyloglucan component of the plant cell wall, thereby allowing P. aeruginosa to replicate in the intercellular spaces in a leaf. This work shows how P. aeruginosa, a multi-host opportunistic pathogen, has repurposed a highly conserved “house-keeping” anabolic pathway (trehalose biosynthesis) as a potent virulence factor that allows it to replicate in the intercellular environment of a leaf.

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PLOS Pathogens: Generators of Phenotypic Diversity in the Evolution of Pathogenic Microorganisms (2013)

PLOS Pathogens: Generators of Phenotypic Diversity in the Evolution of Pathogenic Microorganisms (2013) | Plants and Microbes | Scoop.it

All organisms run the gauntlet of Darwinian selection. Poignant examples include microbial pathogens, which must survive and thrive in their hosts. The process of pathogen adaptation to the host is diverse and is now known to involve a panoply of diversity generators, such as sexual/parasexual reproduction, aneuploidy, prions, mutators, telomeric silencing/recombination, and Hsp90 as a capacitor for evolution. Given the vast diversity of known mechanisms that can generate phenotypic and genotypic assortments, others likely remain to be discovered.


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Plant J: Activity profiling of vacuolar processing enzymes reveals a role for VPE during oomycete infection (2012)

Plant J: Activity profiling of vacuolar processing enzymes reveals a role for VPE during oomycete infection (2012) | Plants and Microbes | Scoop.it

Vacuolar processing enzymes (VPEs) are important cysteine proteases that are implicated in the maturation of seed storage proteins, and programmed cell death during plant–microbe interactions and development. Here, we introduce a specific, cell-permeable, activity-based probe for VPEs. This probe is highly specific for all four Arabidopsis VPEs, and labeling is activity-dependent, as illustrated by sensitivity for inhibitors, pH and reducing agents. We show that the probe can be used for in vivo imaging and displays multiple active isoforms of VPEs in various tissues and in both monocot and dicot plant species. Thus, VPE activity profiling is a robust, simple and powerful tool for plant research for a wide range of applications. Using VPE activity profiling, we discovered that VPE activity is increased during infection with the oomycete pathogen Hyaloperonospora arabidopsidis (Hpa). The enhanced VPE activity is host-derived and EDS1-independent. Sporulation of Hpa is reduced on vpe mutant plants, demonstrating a role for VPE during compatible interactions that is presumably independent of programmed cell death. Our data indicate that, as an obligate biotroph, Hpa takes advantage of increased VPE activity in the host, e.g. to mediate protein turnover and nutrient release.

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Cell Host & Microbe: A Receptor-like Cytoplasmic Kinase Targeted by a Plant Pathogen Effector Is Directly Phosphorylated by the Chitin Receptor and Mediates Rice Immunity (2013)

Cell Host & Microbe: A Receptor-like Cytoplasmic Kinase Targeted by a Plant Pathogen Effector Is Directly Phosphorylated by the Chitin Receptor and Mediates Rice Immunity (2013) | Plants and Microbes | Scoop.it

CERK1 is a lysine motif-containing plant pattern recognition receptor for chitin and peptidoglycan. Chitin recognition by OsCERK1 triggers rapid engagement of a rice MAP kinase cascade, which leads to defense response activation. How the MAP kinase cascades are engaged downstream of OsCERK1 remains obscure. Searching for host proteins that interact with Xoo1488, an effector of the rice pathogenXanthomonas oryzae, we identified the rice receptor-like cytoplasmic kinase, OsRLCK185. Silencing OsRLCK185 suppressed peptidoglycan- and chitin-induced immune responses, including MAP kinase activation and defense-gene expression. In response to chitin, OsRLCK185 associates with, and is directly phosphorylated by, OsCERK1 at the plasma membrane. Xoo1488 inhibits peptidoglycan- and chitin-induced immunity and pathogen resistance. Additionally, OsCERK1-mediated phosphorylation of OsRLCK185 is suppressed by Xoo1488, resulting in the inhibition of chitin-induced MAP kinase activation. These data support a role for OsRLCK185 as an essential immediate downstream signaling partner of OsCERK1 in mediating chitin- and peptidoglycan-induced plant immunity.

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Wine Folly: There’s Still No Cure For Grape Phylloxera (2013)

Wine Folly: There’s Still No Cure For Grape Phylloxera (2013) | Plants and Microbes | Scoop.it

A scourge erupted in Europe that nearly destroyed every single wine grape in the world. In the late 1800s, wineries all over Europe ripped up and burned their family’s ancient vineyards in a desperate attempt to stop the spread of disease. By the 1900s Phylloxera had taken a beyond-imaginable toll: over 70% of the vines in France were dead –the livelyhoods of thousands of families were ruined.

 

What is Grape Phylloxera? Phylloxera is a microscopic louse or aphid, that lives on and eats roots of grapes. It can infest a vineyard by the soles vineyard worker’s boots or naturally spreading from vineyard-to-vineyard by proximity.

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#FUNGAL2013 27th Fungal Genetics Conference, Asilomar, 2013 (with images, tweets)

Tweets from the 27th Fungal Genetics Conference, Asilomar, 2013 http://www.fungalgenetics.org/2013/ ;

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PLOS Pathogens: Genome-wide Prediction and Functional Validation of Promoter Motifs Regulating Gene Expression in Spore and Infection Stages of Phytophthora infestans (2013)

PLOS Pathogens: Genome-wide Prediction and Functional Validation of Promoter Motifs Regulating Gene Expression in Spore and Infection Stages of Phytophthora infestans (2013) | Plants and Microbes | Scoop.it

Most eukaryotic pathogens have complex life cycles in which gene expression networks orchestrate the formation of cells specialized for dissemination or host colonization. In the oomycete Phytophthora infestans, the potato late blight pathogen, major shifts in mRNA profiles during developmental transitions were identified using microarrays. We used those data with search algorithms to discover about 100 motifs that are over-represented in promoters of genes up-regulated in hyphae, sporangia, sporangia undergoing zoosporogenesis, swimming zoospores, or germinated cysts forming appressoria (infection structures). Most of the putative stage-specific transcription factor binding sites (TFBSs) thus identified had features typical of TFBSs such as position or orientation bias, palindromy, and conservation in related species. Each of six motifs tested in P. infestans transformants using the GUS reporter gene conferred the expected stage-specific expression pattern, and several were shown to bind nuclear proteins in gel-shift assays. Motifs linked to the appressoria-forming stage, including a functionally validated TFBS, were over-represented in promoters of genes encoding effectors and other pathogenesis-related proteins. To understand how promoter and genome architecture influence expression, we also mapped transcription patterns to the P. infestans genome assembly. Adjacent genes were not typically induced in the same stage, including genes transcribed in opposite directions from small intergenic regions, but co-regulated gene pairs occurred more than expected by random chance. These data help illuminate the processes regulating development and pathogenesis, and will enable future attempts to purify the cognate transcription factors.

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Mol Microbiol: GK4, a G-protein-coupled receptor with a phosphatidylinositol phosphate kinase domain in Phytophthora infestans, is involved in sporangia development and virulence (2013)

Mol Microbiol: GK4, a G-protein-coupled receptor with a phosphatidylinositol phosphate kinase domain in Phytophthora infestans, is involved in sporangia development and virulence (2013) | Plants and Microbes | Scoop.it

For dispersal and host infection plant pathogens largely depend on asexual spores. Pathogenesis and sporulation are complex processes that are governed by cellular signalling networks including G-protein and phospholipid signalling. Oomycetes possess a family of novel proteins called GPCR-PIPKs (GKs) that are composed of a seven-transmembrane spanning (7-TM) domain fused to a phosphatidylinositol phosphate kinase (PIPK) domain. Based on this domain structure GKs are anticipated to link G-protein and phospholipid signal pathways; however, their functions are currently unknown. Expression analyses of the 12 GK genes in Phytophthora infestans and their orthologues in Phytophthora sojae, revealed differential expression during asexual development. PiGK1 and PiGK4 were fused to monomeric red fluorescent protein (mRFP) and ectopically expressed in P. infestans. In growing hyphae different subcellular distribution patterns were observed indicating that these two GKs act independently during development. We focused on the functional analyses of PiGK4. Its localization suggested involvement in cell differentiation and elongation and its 7-TM domain showed a canonical GPCR membrane topology. Silencing of GK4 and overexpression of full-length and truncated constructs in P. infestans revealed that PiGK4 is not only involved in spore germination and hyphal elongation but also in sporangia cleavage and infection.

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PLOS Computational Biology: Computational Predictions Provide Insights into the Biology of TAL Effector Target Sites (2013)

PLOS Computational Biology: Computational Predictions Provide Insights into the Biology of TAL Effector Target Sites (2013) | Plants and Microbes | Scoop.it

Transcription activator-like (TAL) effectors are injected into host plant cells by Xanthomonasbacteria to function as transcriptional activators for the benefit of the pathogen. The DNA binding domain of TAL effectors is composed of conserved amino acid repeat structures containing repeat-variable diresidues (RVDs) that determine DNA binding specificity. In this paper, we present TALgetter, a new approach for predicting TAL effector target sites based on a statistical model. In contrast to previous approaches, the parameters of TALgetter are estimated from training data computationally. We demonstrate that TALgetter successfully predicts known TAL effector target sites and often yields a greater number of predictions that are consistent with up-regulation in gene expression microarrays than an existing approach, Target Finder of the TALE-NT suite. We study the binding specificities estimated by TALgetter and approve that different RVDs are differently important for transcriptional activation. In subsequent studies, the predictions of TALgetter indicate a previously unreported positional preference of TAL effector target sites relative to the transcription start site. In addition, several TAL effectors are predicted to bind to the TATA-box, which might constitute one general mode of transcriptional activation by TAL effectors. Scrutinizing the predicted target sites of TALgetter, we propose several novel TAL effector virulence targets in rice and sweet orange. TAL-mediated induction of the candidates is supported by gene expression microarrays. Validity of these targets is also supported by functional analogy to known TAL effector targets, by an over-representation of TAL effector targets with similar function, or by a biological function related to pathogen infection. Hence, these predicted TAL effector virulence targets are promising candidates for studying the virulence function of TAL effectors. TALgetter is implemented as part of the open-source Java library Jstacs, and is freely available as a web-application and a command line program.


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The Sunday Times: Chestnut blight threatens UK (2013)

The Sunday Times: Chestnut blight threatens UK (2013) | Plants and Microbes | Scoop.it

Tree-growers and countryside groups fear that sweet chestnuts brought in from continental Europe could carry a fungal disease that would threaten trees in the UK, destroying woodlands, businesses and wildlife habitats. The disease, caused by the fungus Cryphonectria parasitica, has struck twice in England in the past two years, when 180 trees were destroyed after being infected by trees imported from France. In 2011, 150 infected trees were found in Warwickshire and there was a further outbreak affecting 30 trees in East Sussex last year. The Forestry Commission says there are no current cases of sweet chestnut blight, but growers fear that rising demand for sweet chestnut imports — as an alternative to ash in woodlands — poses a risk to UK woodland.

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Phytopathology News: Editor's Corner: Death by Fungus (2013)

Phytopathology News: Editor's Corner: Death by Fungus (2013) | Plants and Microbes | Scoop.it

My column title this month is taken from a subheading in the January 10, 2013, issue of Nature. The full article, entitled “It could happen one night” and written by Nicola Jones, is subtitled “Catastrophes from the past will strike again—We just do not know when.” The article is a followup to the World Economic Forum’s 2013 global risk report and discusses X factors: low-probability, high-impact risks that could threaten life on earth, including super volcanoes, x-ray bursts, tsunamis, and, what caught my attention, fungi.

In the article, Jones states that while bacteria and viruses get more media attention, fungi are in fact the planet’s biggest killer, causing 70% of the recorded global and regional extinctions. She briefly mentions the current fungal threats to amphibians, bats, and bees and gives a quick recount of the Irish potato famine and the death of one million Irish people caused by the attack on the Irish potato crop by Phytophthora infestans (now removed from the fungi, but still frequently grouped with them).

 

She also discusses how potato blight is still a threat with the highly aggressive 13_A2 strain now rampant in Europe and North Africa. The Ug99 superstrain of wheat rust also gets a mention. Less than three weeks later, another article, this time in Nature News, caught my eye. Written by Daniel Cressey, its title was “Coffee rust regains foothold.” Cressey reports that, “Where there is coffee, there is ‘coffee rust.’ But the long stalemate between growers and the fungus behind the devastating disease has broken—with the fungus taking the advantage.” Estimates from the Institute of Coffee of Costa Rica are that as much as half of the 2013–2014 harvest may be lost in the hardest-hit regions of the country due to the severity of the current epidemic. Foliage loss in the current year will affect the size of the following year’s crop. While some progress is being made in combating the disease, especially in Colombia, much work remains to be done.

 

Coffee rust, of course, has long been considered one of the classic diseases studied by plant pathologists. E. C. Large, in The Advance of the Fungi, devotes 12 pages to the 1870s coffee rust epidemic on Ceylon. In rereading Large’s chapter, I was reminded that the coffee rust epidemic not only had the social and economic consequences of shifting the British empire to a culture of tea drinkers, but it was also in the study of the disease that Harry Marshall Ward observed that in order for toxic materials such as lime and sulfur dust to be effective they must “already (be) on the leaves when the spores were germinating, at which period the delicate tubes were easily destroyed and offered scarcely any resistance to weak caustic or poisonous solutions.” Thus was born the concept of preventive treatment of foliage with fungicides.

 

APS members Gail Schumann and Cleo D’Arcy also pay coffee rust due homage in their book, Essential Plant Pathology, listing it as a “Disease Classic.” I was particularly impressed with the supplemental information contained on the accompanying CD. There are excellent photos of symptoms, a reproduction of Berkeley’s original drawing, a life cycle stylization, a discussion of disease management principles, and in my opinion, a wonderful section on the history and economic impact of the disease. According to some estimates, losses to coffee rust on Ceylon in 1878 were approximately £2,000,000, which would be well over $320 million in today’s dollars. For all of us plant pathologists, the current outbreak of coffee rust in Central America is a reminder that our work is never done. We must remain vigilant for the development of epidemics of diseases we have long battled and, at the same time, the development of new strains of pathogens that we thought we had beaten.

 

Doug Jardine, Kansas State University

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New Phytologist: Meeting Report: Bridging mycorrhizal genomics, metagenomics and forest ecology (2013)

New Phytologist: Meeting Report: Bridging mycorrhizal genomics, metagenomics and forest ecology (2013) | Plants and Microbes | Scoop.it

6th New Phytologist Workshop, in Nancy, France, November 15–16, 2012

 

After an initial lag phase dedicated to the sequencing of easily cultured saprotrophic fungi (among the first three published genomes were the models Saccharomyces cerevisiae, Schizosaccharomyces pombe and Neurospora crassa) and species of biomedical, agricultural or biotechnological interest, genomics is now poised to rapidly permeate the fields of fungal ecology and evolution. As regards mycorrhizal associations, the story begins in 2008 with the publication of the genome of the agaric Laccaria bicolor (Martin et al., 2008), followed 2 yr later by publication of the Black Truffle of Périgord Tuber melanosporum genome (Martin et al., 2010). Within the last 2 yr, the Joint Genome Institute (JGI; http://jgi.doe.gov/) of the US Department of Energy has made available to the scientific community the genomes of at least a dozen additional mycorrhizal species and many more are expected to be released in the near future. Mycorrhizal fungal genome projects are part of an initiative for systematic sequencing of species representative of ecological important functional groups, including plant pathogens and wood rotters and will cover all major fungal phyla.

 

‘… fungal genomics … is serving as an inspiration for all scientists engaged in the various aspects of interactions between fungi and plants …’

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Trehalose or Glycogen / alpha-Glucan? Comment about PLOS Pathogens 'Trehalose Promotes Pseudomonas Pathogenicity in Plants' (2013)

Trehalose or Glycogen / alpha-Glucan? Comment about PLOS Pathogens 'Trehalose Promotes Pseudomonas Pathogenicity in Plants' (2013) | Plants and Microbes | Scoop.it

We would like to make the authors aware of some recent developments in the understanding of trehalose and glycogen metabolism in bacteria, which have been missed by the authors, but will likely have a profound effect on the interpretation of the reported observations. A few years ago, trehalose synthase was shown to be the first enzyme in a new metabolic pathway from trehalose to glycogen-like alpha-glucan, now known as the GlgE pathway (J Biol Chem 2010, 285:9803, http://www.ncbi.nlm.nih.g... Nature Chem. Biol. 2010, 6:376, http://www.ncbi.nlm.nih.g...). The GlgE pathway has been shown to be widespread among bacteria including Pseudomonas aeruginosa (Microbiology 2011, 157:1565, http://www.ncbi.nlm.nih.g...). Furthermore, this organism was highlighted as one where the trehalose synthase gene was fused with that of maltose kinase, the second enzyme of the GlgE pathway, and that the fused gene was clustered with the other two genes associated with the GlgE pathway. Finally, evidence is growing that in organisms that possess the GlgE pathway, trehalose synthase does not make trehalose, as was once assumed to be a true in all organisms, but consumes it (from genetics cited above and thermodynamics; J Biol Chem 2011, 286:38298, http://www.ncbi.nlm.nih.g...). The fusion of trehalose synthase with maltose kinase in P. aeruginosa strongly suggests this is the case in this bacterium. This, and other long known aspects of glycogen metabolism in bacteria, will likely have far reaching consequences for the interpretation of the work presented by Djonovic et al.

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Farmers Weekly: Yellow rust lies dormant waiting for warm spell (2013)

Farmers Weekly: Yellow rust lies dormant waiting for warm spell (2013) | Plants and Microbes | Scoop.it

[UK] This week's cold spell may have reduced the yellow rust threat and bought growers some time, but the threat remains and susceptible varieties may need treating once it warms up.  Last week Frontier agronomists highlighted there had been a spate of yellow rust reports in Lincolnshire and Cambridgeshire and warned that farmers may need to go on with a pre-T0 spray.

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The 12th World Congress on Parasitic Plants, 15-20 July 2013, Sheffield, United Kingdom

The 12th World Congress on Parasitic Plants, 15-20 July 2013, Sheffield, United Kingdom | Plants and Microbes | Scoop.it

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PLOS ONE: Evolutionary History of the Plant Pathogenic Bacterium Xanthomonas axonopodis (2013)

PLOS ONE: Evolutionary History of the Plant Pathogenic Bacterium Xanthomonas axonopodis (2013) | Plants and Microbes | Scoop.it

Deciphering mechanisms shaping bacterial diversity should help to build tools to predict the emergence of infectious diseases. Xanthomonads are plant pathogenic bacteria found worldwide. Xanthomonas axonopodis is a genetically heterogeneous species clustering, into six groups, strains that are collectively pathogenic on a large number of plants. However, each strain displays a narrow host range. We address the question of the nature of the evolutionary processes – geographical and ecological speciation – that shaped this diversity. We assembled a large collection of X. axonopodis strains that were isolated over a long period, over continents, and from various hosts. Based on the sequence analysis of seven housekeeping genes, we found that recombination occurred as frequently as point mutation in the evolutionary history of X. axonopodis. However, the impact of recombination was about three times greater than the impact of mutation on the diversity observed in the whole dataset. We then reconstructed the clonal genealogy of the strains using coalescent and genealogy approaches and we studied the diversification of the pathogen using a model of divergence with migration. The suggested scenario involves a first step of generalist diversification that spanned over the last 25 000 years. A second step of ecology-driven specialization occurred during the past two centuries. Eventually, secondary contacts between host-specialized strains probably occurred as a result of agricultural development and intensification, allowing genetic exchanges of virulence-associated genes. These transfers may have favored the emergence of novel pathotypes. Finally, we argue that the largest ecological entity within X. axonopodis is the pathovar.

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Nature Reviews Microbiology: Speak, friend, and enter: signalling systems that promote beneficial symbiotic associations in plants (2013)

Nature Reviews Microbiology: Speak, friend, and enter: signalling systems that promote beneficial symbiotic associations in plants (2013) | Plants and Microbes | Scoop.it

Plants associate with a wide range of microorganisms, with both detrimental and beneficial outcomes. Central to plant survival is the ability to recognize invading microorganisms and either limit their intrusion, in the case of pathogens, or promote the association, in the case of symbionts. To aid in this recognition process, elaborate communication and counter-communication systems have been established that determine the degree of ingress of the microorganism into the host plant. In this Review, I describe the common signalling processes used by plants during mutualistic interactions with microorganisms as diverse as arbuscular mycorrhizal fungi and rhizobial bacteria.


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Sohini Guha's comment, April 11, 2013 10:07 AM
sohiniguha1985@gmail.com
Jennifer Mach's comment, April 11, 2013 10:54 AM
Dear Sohini, I generally have better luck asking for a reprint directly from the corresponding author. Good luck! I don't have library access either, so I feel your pain!
Sohini Guha's comment, April 11, 2013 1:14 PM
thanx jennifer....
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Washington Post: Genetically modified potatoes are studied, criticized in Ireland (2013)

Washington Post: Genetically modified potatoes are studied, criticized in Ireland (2013) | Plants and Microbes | Scoop.it

Some see uber-tubers as the way to avoid the blight that caused the Great Famine, but others are skeptical.

 

Carlow, Ireland — Ewen Mullins is the face of modern Ireland: Young, cosmopolitan, highly educated, he is a plant scientist whose work on a genetically modified potato inherently looks to the future. But Mullins also must think back to one of Ireland’s darkest chapters, the Great Famine of the 1840s. “It’s always there,” he said. “It’s not something we forget or something we should be allowed to forget.”

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Mol Microbiol: Chemotaxis and oospore formation in Phytophthora sojae are controlled by G-protein-coupled receptors with a phosphatidylinositol phosphate kinase domain (2013)

Mol Microbiol: Chemotaxis and oospore formation in Phytophthora sojae are controlled by G-protein-coupled receptors with a phosphatidylinositol phosphate kinase domain (2013) | Plants and Microbes | Scoop.it

G-protein-coupled receptors (GPCRs) are key cellular components that mediate extracellular signals into intracellular responses. Genome mining revealed that Phytophthora spp. have over 60 GPCR genes among which a prominent class of 12 encoding novel proteins with an N-terminal GPCR domain fused to a C-terminal phosphatidylinositol phosphate kinase (PIPK) domain. This study focuses on two GPCR-PIPKs (GKs) in Phytophthora sojae. PsGK4 and PsGK5 are differentially expressed during the life cycle with the highest expression in cysts and during cyst germination, and at late infection stages. In P. sojae transformants that constitutively express RFP-tagged PsGK4 andPsGK5, the fusion proteins in hyphae reside in small, rapidly moving vesicular-like structures. Functional analysis using gene silencing showed that PsGK4-silenced transformants displayed higher levels of encystment and a reduced cyst germination rate when compared with the recipient strain. Moreover, GK4 deficiency (or reduction) resulted in severe defects in zoospore chemotaxis towards isoflavones and soybean roots. In contrast, PsGK5-silenced transformants exhibited no obvious defects in asexual development but oospore production was severely impaired. Both, PsGK4- and PsGK5-silenced transformants showed reduced pathogenicity. These results point to involvement of GKs in zoospore behaviour, chemotaxis and oospore development, and suggest that PsGK4 and PsGK5 each head independent signalling pathways.

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