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

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

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

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The Independent: Wheat rust: The fungal disease that threatens to destroy the world crop (2014)

The Independent: Wheat rust: The fungal disease that threatens to destroy the world crop (2014) | Plants and Microbes | Scoop.it
Experts in Europe and Africa are racing to develop resistant grain varieties as university researchers predict the likely spread across continents of the air-borne spores of the fungus ---- Scientists are warning that wheat is facing a serious threat from a fungal disease that could wipe out the world’s crop if not quickly contained. Wheat rust, a devastating disease known as the “polio of agriculture”, has spread from Africa to South and Central Asia, the Middle East and Europe, with calamitous losses for the world’s second most important grain crop, after rice. There is mounting concern at the dangers posed to global food security.Experts have been aware of the threat since a major epidemic swept across North America’s wheat belt in the 1950s, destroying up to 40 per cent of the crop. Since then, tens of millions of pounds have been invested in developing rust-resistant varieties of the grain. However, an outbreak in Uganda in 1999 was discovered to have been caused by a virulent mutation of the fungus. There has been alarm at the speed at which further mutations have subsequently developed and spread across continents.Plant scientists in Britain estimate the latest developments mean that 90 per cent of all current African wheat varieties are now vulnerable to the disease.
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Figshare: Agrobacterium tumefaciens does not transform guard cells in Nicotiana benthamiana (2014)

Figshare: Agrobacterium tumefaciens does not transform guard cells in Nicotiana benthamiana (2014) | Plants and Microbes | Scoop.it

The bacterium Agrobacterium tumefaciens is widely used to genetically transform leaf cells of Nicotiana benthamiana using the agroinfiltration method. Interestingly, A. tumefaciens does not transform guard cells, whereas it transforms efficiently pavement cells. The high chlorophyll content makes chloroplasts autofluorescent. In the case of live-cell imaging experiments with leaf cells transiently expressing fluorescent markers targeted to chloroplasts, it is hard to differentiate the fluorescent marker signal from chlorophyll autofluorescence. Here, I show that guard cells can be used to differentiate those. A GFP targeted to the chloroplast stroma was transiently expressed in N. benthamiana leaf cells, and epidermis cells were observed by live-cell imaging with a laser-scanning confocal microscope two days after the agro-infiltration. A 488 nm wavelength was used to illuminate the tissues, and GFP and chlorophyll signals were collected between 505-525 nm and 680-700 nm, respectively. The asterisks mark the guard cells, the cross marks a non-transformed pavement cell. The white rectangle on the merged image delimitates the close-ups presented in the lower panel. Note the absence of GFP signal in chloroplasts from the guard cells and from the non-transformed pavement cell.

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New Phytologist: Virtual Special Issue on phytopathogen effector proteins (2014)

New Phytologist: Virtual Special Issue on phytopathogen effector proteins (2014) | Plants and Microbes | Scoop.it

Upon analysis of phytopathogen genomes it turned out that phytopathogenic microbes typically express dozens (bacteria; Collmer et al., 2009) to hundreds (oomycetes and fungi; Schmidt & Panstruga, 2011) of effector proteins. They often do not share any considerable sequence relatedness to known proteins and therefore can be considered as ‘pioneer proteins’, which renders their functional analysis a formidable task. Nevertheless, owing to the key role effector proteins play in plant–microbe interactions, their molecular analysis lately became very popular and is a flourishing research field. This development, which is evidenced by the substantial increase in literature devoted to ‘effectors’ during the last decade (Fig. 1), has also been appreciated by New Phytologist as documented by the organization of two symposia, in 2009 and 2012, with an emphasis on effectors in plant–microbe interactions (22nd New Phytologist Symposium and 30th New Phytologist Symposium; Lee et al., 2013). Besides proteinaceous effectors, secreted small molecules can also exhibit effector activity. Prominent examples from the phytopathogenic bacterium Pseudomonas syringae comprise syringolin (a proteasome inhibitor) and coronatine (a mimic of the phytohormone jasmonic acid), but also fungal secondary metabolites can have defense-suppressing activities (e.g. host-selective toxins; Tsuge et al., 2013).


In this Virtual Special Issue we compile a number of papers that were published recently in New Phytologist which all deal with various aspects of effector biology, ranging from bacterial to oomycete and fungal as well as nematode effectors. These papers cover effector functions related to suppression of plant immune responses as well as nutrient acquisition and the identification of plant effector targets.

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Mol Microbiology: Histone H3K9 and H3K27 methylation regulates fungal alkaloid biosynthesis in a fungal endophyte–plant symbiosis (2014)

Mol Microbiology: Histone H3K9 and H3K27 methylation regulates fungal alkaloid biosynthesis in a fungal endophyte–plant symbiosis (2014) | Plants and Microbes | Scoop.it

Epichloё festucae is a filamentous fungus that forms a mutually beneficial symbiotic association with Lolium perenne. This endophyte synthesizes bioprotective lolitrems (ltm) and ergot alkaloids (easin planta but the mechanisms regulating expression of the corresponding subtelomeric gene clusters are not known. We show here that the status of histone H3 lysine 9 and lysine 27 trimethylation (H3K9me3/H3K27me3) at these alkaloid gene loci are critical determinants of transcriptional activity. Using ChIP-qPCR we found that levels of H3K9me3 and H3K27me3 were reduced at these loci in plant infected tissue compared to axenic culture. Deletion of E. festucae genes encoding the H3K9- (ClrD) or H3K27- (EzhB) methyltransferases led to derepression of ltm and eas gene expression under non-symbiotic culture conditions and a further enhancement of expression in the double deletion mutant. These changes in gene expression were matched by corresponding reductions in H3K9me3 and H3K27me3 marks. Both methyltransferases are also important for the symbiotic interaction between E. festucae and L. perenne. Our results show that the state of H3K9 and H3K27 trimethylation of E. festucae chromatin is an important regulatory layer controlling symbiosis-specific expression of alkaloid bioprotective metabolites and the ability of this symbiont to form a mutualistic interaction with its host.

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PLOS Biology: Phytoplasma Effector SAP54 Hijacks Plant Reproduction by Degrading MADS-box Proteins and Promotes Insect Colonization in a RAD23-Dependent Manner (2014)

PLOS Biology: Phytoplasma Effector SAP54 Hijacks Plant Reproduction by Degrading MADS-box Proteins and Promotes Insect Colonization in a RAD23-Dependent Manner (2014) | Plants and Microbes | Scoop.it

Pathogens that rely upon multiple hosts to complete their life cycles often modify behavior and development of these hosts to coerce them into improving pathogen fitness. However, few studies describe mechanisms underlying host coercion. In this study, we elucidate the mechanism by which an insect-transmitted pathogen of plants alters floral development to convert flowers into vegetative tissues. We find that phytoplasma produce a novel effector protein (SAP54) that interacts with members of the MADS-domain transcription factor (MTF) family, including key regulators SEPALLATA3 and APETALA1, that occupy central positions in the regulation of floral development. SAP54 mediates degradation of MTFs by interacting with proteins of the RADIATION SENSITIVE23 (RAD23) family, eukaryotic proteins that shuttle substrates to the proteasome. Arabidopsis rad23 mutants do not show conversion of flowers into leaf-like tissues in the presence of SAP54 and during phytoplasma infection, emphasizing the importance of RAD23 to the activity of SAP54. Remarkably, plants with SAP54-induced leaf-like flowers are more attractive for colonization by phytoplasma leafhopper vectors and this colonization preference is dependent on RAD23. An effector that targets and suppresses flowering while simultaneously promoting insect herbivore colonization is unprecedented. Moreover, RAD23 proteins have, to our knowledge, no known roles in flower development, nor plant defence mechanisms against insects. Thus SAP54 generates a short circuit between two key pathways of the host to alter development, resulting in sterile plants, and promotes attractiveness of these plants to leafhopper vectors helping the obligate phytoplasmas reproduce and propagate (zombie plants).

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News: Climate change a threat to security, food and humankind - IPCC report (2014)

News: Climate change a threat to security, food and humankind - IPCC report (2014) | Plants and Microbes | Scoop.it

A United Nations report raised the threat of climate change to a whole new level on Monday, warning of sweeping consequences to life and livelihood. The report from the UN's intergovernmental panel on climate change concluded that climate change was already having effects in real time – melting sea ice and thawing permafrost in the Arctic, killing off coral reefs in the oceans, and leading to heat waves, heavy rains and mega-disasters. And the worst was yet to come. Climate change posed a threat to global food stocks, and to human security, the blockbuster report said.


The warning signs about climate change and extreme weather events have been accumulating over time. But this report struck out on relatively new ground by drawing a clear line connecting climate change to food scarcity, and conflict. The report said climate change had already cut into the global food supply. Global crop yields were beginning to decline – especially for wheat – raising doubts as to whether production could keep up with population growth. “It has now become evident in some parts of the world that the green revolution has reached a plateau,” Pachauri said. The future looks even more grim. Under some scenarios, climate change could lead to dramatic drops in global wheat production as well as reductions in maize. "Climate change is acting as a brake. We need yields to grow to meet growing demand, but already climate change is slowing those yields," said Michael Oppenheimer, a Princeton professor and an author of the report.


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Schornack Lab: Phytophthora palmivora infection (2014)

Schornack Lab: Phytophthora palmivora infection (2014) | Plants and Microbes | Scoop.it

Infection fireball…Phytophthora palmivora spore droplet on a leaf with outgrowing red fluorescent hyphae. 

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Twitter archive: #ECFG12 12th European Conference on Fungal Genetics, Seville, March 2014

The 12th European Conference on Fungal Genetics, Seville (Spain) during March 23-27, 2014. http://www.ecfg12.com/

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MPMI: Pseudomonas syringae evades host immunity by degrading flagellin monomers with alkaline protease AprA (2014)

MPMI: Pseudomonas syringae evades host immunity by degrading flagellin monomers with alkaline protease AprA (2014) | Plants and Microbes | Scoop.it

Bacterial flagellin molecules are strong inducers of innate immune responses in both mammals and plants. The opportunistic pathogenPseudomonas aeruginosa secretes an alkaline protease called AprA that degrades flagellin monomers. Here, we show that AprA is widespread among a wide variety of bacterial species. In addition we investigated the role of AprA in virulence of the bacterial plant pathogen Pseudomonas syringae pv. tomato DC3000 (Pst). The AprA-deficient Pst ∆aprA knockout mutant was significantly less virulent on both tomato and A. thaliana. Moreover, infiltration of A. thaliana Col-0 leaves with Pst ∆aprA evoked a significantly higher level of expression of the defense-related genes FRK1 and PR-1 than did wild-type Pst. In the flagellin receptor mutant fls2, pathogen virulence and defense-related gene activation did not differ between Pst and Pst ∆aprA. Together, these results suggest that AprA of Pst is important for evasion of recognition by the FLS2 receptor, allowing wild-type Pst to be more virulent on its host plant than AprA-deficient Pst ∆aprA. To provide further evidence for the role of Pst AprA in host immune evasion, we overexpressed the AprA inhibitory peptide AprI of Pst in A. thaliana to counteract the immune evasive capacity of Pst AprA. Ectopic expression of aprI in A. thaliana resulted in an enhanced level of resistance against wild-type Pst, while the already elevated level of resistance against Pst ∆aprA remained unchanged. Together, these results indicate that evasion of host immunity by the alkaline protease AprA is important for full virulence of Pst and likely acts by preventing flagellin monomers from being recognized by its cognate immune receptor.

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COST Action SUSTAIN Workshop on structure-guided investigation of effector function, action and recognition. Bucharest, Romania, 10-12 September, 2014

COST Action SUSTAIN Workshop on structure-guided investigation of effector function, action and recognition. Bucharest, Romania, 10-12 September, 2014 | Plants and Microbes | Scoop.it

In contrast to the vast amount of genomic information, knowledge on the structure of protein-based molecular machines working within the cell, their interactions and processing is scarce and far more difficult to obtain. Structural methods, including molecular modeling and simulation shed light onto the molecular details of protein-protein and protein-peptide  interactions proving useful in designing strategies to control the cellular processes in which these interactions occur. Hence  structural approaches might become highly relevant for a better understanding and control ofplant-pathogen interactions. In particular, the Workshop  "Structure-guided investigation of Effector function, action and recognition" aims to assess the state of the art and evaluate the potential of structural techniques in the field and in the effort of designing strategies to preventing pathogen infection. For this, the workshopwill focus on:


- Effector and host proteins: identification, biophysics and biochemistry of protein action and interactions


- Structural experiments on proteins involved in plant-pathogen interactions


- Structural bioinformatics, probailistic modelling and experimental validation


- Modelling protein-protein and interdomanin interactions using combined bioinformatics, structural analysis, experimental constraints and simulation


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MPMI: HopZ4 from Pseudomonas syringae, a member of the HopZ type III effector family from the YopJ superfamily, inhibits the proteasome in plants (2014)

MPMI: HopZ4 from Pseudomonas syringae, a member of the HopZ type III effector family from the YopJ superfamily, inhibits the proteasome in plants (2014) | Plants and Microbes | Scoop.it

The YopJ-family of type III effector (T3E) proteins is one of the largest and widely distributed families of effector proteins whose members are highly diversified in virulence functions. In the present study, HopZ4, a member of the YopJ-family of T3Es from the cucumber pathogen Pseudomonas syringae pv. lachrymans is described. HopZ4 shares high sequence similarity with the Xanthomonas T3E XopJ and a functional analysis suggests a conserved virulence function between these two T3Es. As has previously shown for XopJ, HopZ4 interacts with the proteasomal subunit RPT6 in yeast and in planta to inhibit proteasome activity during infection. The inhibitory effect on the proteasome is dependent on localization of HopZ4 to the plasma membrane as well as on an intact catalytic triad of the effector protein. Furthermore, HopZ4 is able to complement loss of XopJ in Xanthomonas as it prevents precocious host cell death during a compatible interaction of Xanthomonas with pepper. The data presented here suggest that different bacterial species employ inhibition of the proteasome as a virulence strategy by making use of conserved T3Es from the YopJ-family of bacterial effector proteins.


Via Suayib Üstün
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PLOS Pathogens: Dimerization of VirD2 Binding Protein Is Essential for Agrobacterium Induced Tumor Formation in Plants (2014)

PLOS Pathogens: Dimerization of VirD2 Binding Protein Is Essential for Agrobacterium Induced Tumor Formation in Plants (2014) | Plants and Microbes | Scoop.it

The Type IV Secretion System (T4SS) is the only bacterial secretion system known to translocate both DNA and protein substrates. The VirB/D4 system from Agrobacterium tumefaciens is a typical T4SS. It facilitates the bacteria to translocate the VirD2-T-DNA complex to the host cell cytoplasm. In addition to protein-DNA complexes, the VirB/D4 system is also involved in the translocation of several effector proteins, including VirE2, VirE3 and VirF into the host cell cytoplasm. These effector proteins aid in the proper integration of the translocated DNA into the host genome. The VirD2-binding protein (VBP) is a key cytoplasmic protein that recruits the VirD2–T-DNA complex to the VirD4-coupling protein (VirD4 CP) of the VirB/D4 T4SS apparatus. Here, we report the crystal structure and associated functional studies of the C-terminal domain of VBP. This domain mainly consists of α-helices, and the two monomers of the asymmetric unit form a tight dimer. The structural analysis of this domain confirms the presence of a HEPN (higher eukaryotes and prokaryotes nucleotide-binding) fold. Biophysical studies show that VBP is a dimer in solution and that the HEPN domain is the dimerization domain. Based on structural and mutagenesis analyses, we show that substitution of key residues at the interface disrupts the dimerization of both the HEPN domain and full-length VBP. In addition, pull-down analyses show that only dimeric VBP can interact with VirD2 and VirD4 CP. Finally, we show that only Agrobacterium harboring dimeric full-length VBP can induce tumors in plants. This study sheds light on the structural basis of the substrate recruiting function of VBP in the T4SS pathway of A. tumefaciens and in other pathogenic bacteria employing similar systems.

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Cell Host and Microbe: The FLS2-Associated Kinase BIK1 Directly Phosphorylates the NADPH Oxidase RbohD to Control Plant Immunity (2014)

Cell Host and Microbe: The FLS2-Associated Kinase BIK1 Directly Phosphorylates the NADPH Oxidase RbohD to Control Plant Immunity (2014) | Plants and Microbes | Scoop.it

The Arabidopsis immune receptor FLS2 senses the bacterial flagellin epitope flg22 to activate transient elevation of cytosolic calcium ions, production of reactive oxygen species (ROS), and other signaling events to coordinate antimicrobial defenses, such as stomatal closure that limits bacterial invasion. However, how FLS2 regulates these signaling events remains largely unknown. Here we show that the receptor-like cytoplasmic kinase BIK1, a component of the FLS2 immune receptor complex, not only positively regulates flg22-triggered calcium influx but also directly phosphorylates theNADPH oxidase RbohD at specific sites in a calcium-independent manner to enhance ROS generation. Furthermore, BIK1 and RbohD form a pathway that controls stomatal movement in response to flg22, thereby restricting bacterial entry into leaf tissues. These findings highlight a direct role of the FLS2 complex in the regulation of RbohD-mediated ROS production and stomatal defense.


Via Suayib Üstün, Guogen Yang, Dr.donkey, Jim Alfano
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Science: Structural Basis for Assembly and Function of a Heterodimeric Plant Immune Receptor (2014)

Science: Structural Basis for Assembly and Function of a Heterodimeric Plant Immune Receptor (2014) | Plants and Microbes | Scoop.it

Cytoplasmic plant immune receptors recognize specific pathogen effector proteins and initiate effector-triggered immunity. In Arabidopsis, the immune receptors RPS4 and RRS1 are both required to activate defense to three different pathogens. We show that RPS4 and RRS1 physically associate. Crystal structures of the N-terminal Toll–interleukin-1 receptor/resistance (TIR) domains of RPS4 and RRS1, individually and as a heterodimeric complex (respectively at 2.05, 1.75, and 2.65 angstrom resolution), reveal a conserved TIR/TIR interaction interface. We show that TIR domain heterodimerization is required to form a functional RRS1/RPS4 effector recognition complex. The RPS4 TIR domain activates effector-independent defense, which is inhibited by the RRS1 TIR domain through the heterodimerization interface. Thus, RPS4 and RRS1 function as a receptor complex in which the two components play distinct roles in recognition and signaling.


See also Perspective by Nishimura and Dangl http://www.sciencemag.org/content/344/6181/267.short

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NY Times: A Green Revolution, This Time for Africa (2014)

NY Times: A Green Revolution, This Time for Africa (2014) | Plants and Microbes | Scoop.it

Last month was the 100th anniversary of the birth of Norman Borlaug, the father of the Green Revolution. In 1944, Borlaug moved to Mexico to work on breeding high-yield, disease-resistant strains of wheat. Mexico adopted them — and in 1970, wheat yields were six times what they had been in 1950. In 1965, India and Pakistan, then on the brink of widespread famine, began growing the high-yield wheat. Over the next 30 years, wheat yields in India tripled. The same happened with high-yield rice strains that had been developed in the Philippines.


Borlaug, who died in 2009, directed the wheat improvement program of the International Maize and Wheat Improvement Center, which goes by the Spanish acronym Cimmyt. The research headquarters is a 78-hectare spread of land a half-hour drive from Mexico City. Today Cimmyt researchers grow and test new varieties of corn, or maize, along with the wheat. Their purpose is to contribute to a new green revolution — this time for Africa.


Read also http://nyti.ms/1ql15i2

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The Economist: The sorceress’s apprentice (2014)

The Economist: The sorceress’s apprentice (2014) | Plants and Microbes | Scoop.it

ANYONE who walks in the woods will be familiar with witches’ brooms (pictured). Many trees sport these bushy tumours, which have a variety of causes. An important one is a group of bacteria called phytoplasma that are, in turn, carried from plant to plant by sap-sucking insects such as leafhoppers.


Phytoplasma do other odd things to plants as well, sometimes including making their flowers develop like leaves. Witches’ brooms and leaf-like flowers provide more of the soft tissue leafhoppers like to suck sap from. Bacteria and bugs have thus developed a symbiosis at the expense of their vegetable hosts, since leaf-like flowers are sterile and a plant so afflicted cannot reproduce.


Saskia Hogenhout of the John Innes Centre in Norwich, Britain, has been investigating this symbiosis—and asking, in particular, just how phytoplasma bacteria hijack a plant’s developmental machinery and make it work to their advantage and the plant’s detriment. Her results, now published in PLOS Biology, are a dark tale of molecular mayhem.


Dr Hogenhout and her team experimented on Arabidopsis, a type of cress that is to plant geneticists what Drosophila, the fruit fly, is to animal geneticists—a species whose genes have been thoroughly investigated and are reasonably well understood. Phytoplasma bacteria, she found, produce a protein called SAP54 that interferes with molecular switches, known as MADS-box transcription factors, which promote flower formation. With these transcription factors switched off, Arabidopsis’s flowers develop bushy leaves similar in form to witches’ brooms.


Further experiments showed that Arabidopsis plants with leafy flowers are indeed, as would be expected, more attractive to leafhoppers. The insects pick up the bacteria as they feed and carry them to other plants, perpetuating the mutually beneficial process. The magic of witches’ brooms is thus demystified.

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Nature News: Bacterial tricks for turning plants into zombies (2014)

Nature News: Bacterial tricks for turning plants into zombies  (2014) | Plants and Microbes | Scoop.it

Many parasites commandeer the bodies of their hosts in order to spread. Examples of this include horsehair worms that reach water by forcing their cricket hosts to drown themselves, and liver flukes that drive infected ants to climb blades of grass, where cows can eat the insects, and so the flukes. But parasites can turn plants into zombies, too — and a team of scientists from the John Innes Centre in Norwich, UK, has now discovered how they do it.


When plants are infected by parasitic bacteria called phytoplasmas, their flowers turn into leafy shoots, their petals turn green and they develop a mass of shoots called ‘witches’ brooms’. This transformation sterilizes the plant, while attracting the sap-sucking insects that carry the bacteria to new hosts. “The plant appears alive, but it’s only there for the good of the pathogen,” says plant pathologist Saskia Hogenhout from the John Innes Centre in Norwich, UK. “In an evolutionary sense, the plant is dead and will not produce offspring.” “Many might baulk at the concept of a zombie plant because the idea of plants behaving is strange,” says David Hughes, a parasitologist at Pennsylvania State University in University Park. “But they do, and since they do, why wouldn't parasites have evolved to take over their behaviour, as they do for ants and crickets?”

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News: Mutant wheat fungus alarms food experts (2014)

News: Mutant wheat fungus alarms food experts (2014) | Plants and Microbes | Scoop.it

Outbreaks of a deadly fungal disease in wheat crops in Germany and Ethiopia in 2013 have had the scientific community buzzing over the threat posed to global food security. Wheat stem rust, also known as wheat black rust, is often referred to as the “polio of agriculture”: The rapidly mutating fungal disease can travel thousands of kilometres and wipe out crops. Wheat farmers and scientists at a recent summit hosted by the Mexico-based International Maize and Wheat Improvement Center (CIMMYT ) have been examining outbreaks of different strains of wheat stem rust in the two countries to identify any similarities.


In Germany “the occurrence of stem rust was favoured by a period of unusually high temperatures… and an unusually late development of the wheat crop due to cold spring and early summer temperatures,” explained Kerstin Flath, senior scientist at Germany’s Federal Research Centre for Cultivated Plants at the Julius Kuehn-Institut. The outbreak occurred in June in central Germany, a mainly wheat producing area, and was the first in the country in several decades.


Then in November 2013 the disease struck a popular variety of wheat in Ethiopia called digalu, used to make bread, said Bekele Abeyo, a senior scientist and wheat breeder at CIMMYT. What was particularly disconcerting for the scientists was that digalu had been bred with inherent resistance to certain strains of stem rust and another wheat disease called “yellow rust” or “stripe”.

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MPMI: Transcriptome Sequencing Uncovers the Avr5 Avirulence Gene of the Tomato Leaf Mould Pathogen Cladosporium fulvum (2014)

MPMI: Transcriptome Sequencing Uncovers the Avr5 Avirulence Gene of the Tomato Leaf Mould Pathogen Cladosporium fulvum (2014) | Plants and Microbes | Scoop.it

The Cf-5 gene of tomato confers resistance to strains of the fungal pathogen Cladosporium fulvum carrying the avirulence gene Avr5. Although Cf-5 has been cloned, Avr5 has remained elusive. We report the cloning of Avr5 using a combined bioinformatic and transcriptome sequencing approach. RNA-Seq was performed on the sequenced race 0 strain (0WU; carries Avr5), as well as a race 5 strain (IPO 1979; lacks a functional Avr5 gene), during infection of susceptible tomato. Forty-four in planta-induced Cfulvum Candidate Effector (CfCE) genes of 0WU were identified that putatively encode a secreted, small cysteine-rich protein. An expressed transcript sequence comparison between strains revealed two polymorphic CfCE genes in IPO 1979. One of these conferred avirulence to IPO 1979 on Cf-5 tomato following complementation with the corresponding 0WU allele, confirming identification of Avr5. Complementation also led to increased fungal biomass during infection of susceptible tomato, signifying a role for Avr5 in virulence. Seven of eight race 5 strains investigated escape Cf-5–mediated resistance through deletion of the Avr5 gene. Avr5 is heavily flanked by repetitive elements, suggesting that repeat instability, in combination with Cf-5–mediated selection pressure, has led to the emergence of race 5 strains deleted for the Avr5 gene.

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MPMI: Single amino acid mutations in the potato immune receptor R3a expand response to Phytophthora effectors (2014)

MPMI: Single amino acid mutations in the potato immune receptor R3a expand response to Phytophthora effectors (2014) | Plants and Microbes | Scoop.it

Both plants and animals rely on nucleotide-binding domain and leucine-rich repeat-containing proteins (NB-LRRs or NLRs) to respond to invading pathogens and activate immune responses. How plant NB-LRR proteins respond to pathogens is poorly understood. We undertook a gain-of-function random mutagenesis screen of the potato NB-LRR immune receptor R3a to study how this protein responds to the effector protein AVR3a from the oomycete pathogen Phytophthora infestans. R3a response can be extended to the stealthy AVR3aEM isoform of the effector while retaining recognition of AVR3aKI. Each one of 8 single amino acid mutations is sufficient to expand the R3a response to AVR3aEM and other AVR3a variants. These mutations occur across the R3a protein, from the N-terminus to different regions of the LRR domain. Further characterization of these R3a mutants revealed that at least one of them was sensitized, exhibiting a stronger response than the wild-type R3a protein to AVR3aKI. Remarkably, the N336Y mutation, near the R3a nucleotide-binding pocket, conferred response to the effector protein PcAVR3a4 from the vegetable pathogen Phytophthora capsici. This work contributes to understanding how NB-LRR receptor specificity can be modulated. Together with knowledge of pathogen effector diversity, this strategy can be exploited to develop synthetic immune receptors.

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Stephen Bolus's curator insight, March 29, 11:09 PM

I just really love the idea of synthetic immune receptors!

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New Phytologist: Cospeciation vs host-shift speciation: methods for testing, evidence from natural associations and relation to coevolution (2013)

New Phytologist: Cospeciation vs host-shift speciation: methods for testing, evidence from natural associations and relation to coevolution (2013) | Plants and Microbes | Scoop.it

Hosts and their symbionts are involved in intimate physiological and ecological interactions. The impact of these interactions on the evolution of each partner depends on the time-scale considered. Short-term dynamics – ‘coevolution’ in the narrow sense – has been reviewed elsewhere. We focus here on the long-term evolutionary dynamics of cospeciation and speciation following host shifts. Whether hosts and their symbionts speciate in parallel, by cospeciation, or through host shifts, is a key issue in host–symbiont evolution. In this review, we first outline approaches to compare divergence between pairwise associated groups of species, their advantages and pitfalls. We then consider recent insights into the long-term evolution of host–parasite and host–mutualist associations by critically reviewing the literature. We show that convincing cases of cospeciation are rare (7%) and that cophylogenetic methods overestimate the occurrence of such events. Finally, we examine the relationships between short-term coevolutionary dynamics and long-term patterns of diversification in host–symbiont associations. We review theoretical and experimental studies showing that short-term dynamics can foster parasite specialization, but that these events can occur following host shifts and do not necessarily involve cospeciation. Overall, there is now substantial evidence to suggest that coevolutionary dynamics of hosts and parasites do not favor long-term cospeciation.

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Book: Plant-Pathogen Interactions: Methods and Protocols (2014)

Book: Plant-Pathogen Interactions: Methods and Protocols (2014) | Plants and Microbes | Scoop.it

Plant-Pathogen Interactions: Methods and Protocols, Second Edition by Paul Birch, John Jones, Jorunn Bos (Editors) expands upon the first edition with current, detailed protocols for the study of plant pathogen genome sequences. It contains new chapters on techniques to help identify and characterize effectors and to study their impacts on host immunity and their roles in pathogen biology. Additional chapters focus on protocols to identify avirulence and resistance genes, investigate the roles of effector targets and other defence-associated proteins in plant immunity. Written in the highly successful Methods in Molecular Biology series format, chapters include introductions to their respective topics, lists of the necessary materials and reagents, step-by-step, readily reproducible laboratory protocols and tips on troubleshooting and avoiding known pitfalls.

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Networks in Immunity Workshop, University of California, Davis, 1-3 April, 2014

Networks in Immunity Workshop, University of California, Davis, 1-3 April, 2014 | Plants and Microbes | Scoop.it

Given the demonstrated importance of the non-RD class of kinases in the immune response, and the large number of these proteins in monocots (rice has approximately 10 times as many non-RD receptor kinases as Arabidopsis), there is great interest in exploring cereal PRR-mediated immunity.


This workshop will be modeled after the highly successful NSF-supported Plant Phosphorylation Workshop that serves as a forum for researchers from as many as 45 laboratories to interact and share research ideas and results.

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Plant Cell: Phytophthora infestans RXLR Effector PexRD2 Interacts with Host MAPKKKε to Suppress Plant Immune Signaling (2014)

Plant Cell: Phytophthora infestans RXLR Effector PexRD2 Interacts with Host MAPKKKε to Suppress Plant Immune Signaling (2014) | Plants and Microbes | Scoop.it

Mitogen-activated protein kinase cascades are key players in plant immune signaling pathways, transducing the perception of invading pathogens into effective defense responses. Plant pathogenic oomycetes, such as the Irish potato famine pathogen Phytophthora infestans, deliver RXLR effector proteins to plant cells to modulate host immune signaling and promote colonization. Our understanding of the molecular mechanisms by which these effectors act in plant cells is limited. Here, we report that the P. infestans RXLR effector PexRD2 interacts with the kinase domain of MAPKKKε, a positive regulator of cell death associated with plant immunity. Expression of PexRD2 or silencing MAPKKKε inNicotiana benthamiana enhances susceptibility to P. infestans. We show that PexRD2 perturbs signaling pathways triggered by or dependent on MAPKKKε. By contrast, homologs of PexRD2 from P. infestans had reduced or no interaction with MAPKKKε and did not promote disease susceptibility. Structure-led mutagenesis identified PexRD2 variants that do not interact with MAPKKKε and fail to support enhanced pathogen growth or perturb MAPKKKε signaling pathways. Our findings provide evidence that P. infestans RXLR effector PexRD2 has evolved to interact with a specific host MAPKKK to perturb plant immunity–related signaling.


Via Suayib Üstün
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Suayib Üstün's curator insight, March 14, 12:52 PM

What a great week for effector biology!!

Freddy Monteiro's comment, March 14, 5:42 PM
Indeed! A crazy week. You guys belong to an excellent generation of scientists.
Rescooped by Kamoun Lab @ TSL from microbial pathogenesis and plant immunity
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Science: A Bacterial Tyrosine Phosphatase Inhibits Plant Pattern Recognition Receptor Activation (2014)

Science: A Bacterial Tyrosine Phosphatase Inhibits Plant Pattern Recognition Receptor Activation (2014) | Plants and Microbes | Scoop.it

Innate immunity relies on the perception of pathogen-associated molecular patterns (PAMPs) by pattern-recognition receptors (PRRs) located on the host cell’s surface. Many plant PRRs are kinases. Here, we report that the Arabidopsis receptor kinase EF-TU RECEPTOR EFR, which perceives the elf18 peptide derived from bacterial elongation factor Tu, is activated upon ligand binding by phosphorylation on its tyrosine residues. Phosphorylation of a single tyrosine residue, Y836, is required for activation of EFR and downstream immunity to the phytopathogenic bacterium Pseudomonas syringae. A tyrosine phosphatase, HopAO1, secreted by P. syringae, reduces EFR phosphorylation and derails subsequent immune responses. Thus host and pathogen battle to take control of PRR tyrosine phosphorylation used to initiate anti-bacterial immunity.


Via Freddy Monteiro, Jim Alfano
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Jim Alfano's curator insight, March 13, 3:21 PM

Very interesting finding - A long sought target of the HopAO1 effector. HopAO1 also suppresses ETI - so additional targets remain undiscovered.