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News: Nature Biotech - Move over ZFNs

A new technology for genome editing may put the zinc finger nuclease franchise out of business, some believe. Not so fast, say the finger people. Laura DeFrancesco reports.

 

In June, Life Technologies of Carlsbad, California, received an exclusive license from the Two Blades Foundation of Evanston, Illinois, and a group of plant biologists from Martin Luther University in Halle, Germany, to commercialize a new genome editing technology—transcription activator-like (TAL) effectors. With the newly announced license spurring on Life Technologies, researchers may soon be able to choose from several commercial sources for designer TAL effectors...

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TSL Summer School Plant Microbe Interactions, 20–29th July 2020 Norwich, UK

TSL Summer School Plant Microbe Interactions, 20–29th July 2020 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 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 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.

 

Topics

 

Effectors
Effectors and Immunity
Resistance Proteins
Infection Processes
Proteomics
Wheat Genetics and Genomics in Plant Innate Immunity
Translations: Tipping the balance

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Conference: ISCLB 2020 – International Symposium on Cereal Leaf Blights 2020

Conference: ISCLB 2020 – International Symposium on Cereal Leaf Blights 2020 | Plants and Microbes | Scoop.it

The International Symposium on Cereal Leaf Blights is co-organized together with the CRP-Wheat Septoria Platform (CIMMYT; ICARDA) and the Institution of Agricultural Research and Higher Education (IRESA). This year’s symposium coincides with the International Year of Plant Health and continues its tradition in providing a unique platform for students, academicians, researchers and practitioners to exchange their ideas, experiences and research results in various aspects on cereal leaf blight diseases. The Symposium will feature plenary and concurrent sessions embracing the challenges and opportunities facing the scientific and the cereal growers’ communities.

 

We are delighted to welcome our distinguished Keynote speakers for the ISCLB2020, and the session Chairs and Co-chairs who will help initiate and guide our discussions across the seven Symposium topics. Presentations, Poster displays, as well as panel discussions, and a networking dinner for all our contributors will open doors to developing long lasting collaborations throughout the world. There will also be an opportunity to participate in a field tour on April 22, 2020 to acquaint participants with Tunisian research platforms, researchers, developers, and farmers; a unique opportunity where we will have public-private sector interactions.

 

The ISCLB 2020 Organizing Committee would like to take this opportunity to thank our generous sponsors and wish you all a wonderful experience.

 

We look forward to your contribution and participation and ultimately meeting you in Yasmine Hammamet!

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MPMI: Focus on Cell Biology of Virus-Plant and Virus-Vector Interactions (2020)

MPMI: Focus on Cell Biology of Virus-Plant and Virus-Vector Interactions (2020) | Plants and Microbes | Scoop.it

A successful viral infection requires complex, compatible molecular interactions between the invading virus and the host. A better understanding of such interactions may assist in the development of novel approaches to control viral diseases for sustainable crop production. In the past decade, the cell biology of virus-host and virus-vector interactions has been one of the most exciting areas of research in the molecular plant-microbe field. This is partially attributed to the availability of powerful cell biology techniques, including imaging tools like confocal microscopy and electron microscopy and tomography. As a result, there has been an unprecedented increase in knowledge in the areas of the bi- and tripartite interactions of virus, host, and vector. We now have a much clearer picture of viral virulence mechanisms, virus-induced host defenses, viral counteracting strategies, and viral circulations in the insect vectors. This Focus Issue highlights molecular virus-plant and virus-vector interactions in the areas of cell biology and closely related disciplines and explores biotechnology-based antiviral strategies using knowledge generated from these research areas.

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Book: Potato late blight in Europe (2020)

Book: Potato late blight in Europe (2020) | Plants and Microbes | Scoop.it

Didier Andrivon from INRA delves into the disease that once killed 1.5 million individuals in Ireland: Potato late blight, also known as Phytophthora Infestans.

 

It would be easy to think that a disease peaking over one hundred years ago is no longer a problem, but potato late blight continues to evolve and emerge in new places – similarly to the insidious reach of anti-microbial resistance.

 

Currently, potato late blight costs the European Union (EU) €1 billion per year.
Andrivon brings us to the essential questions: How can farmers stop the spread of P. Infestans? What is causing the rapid changes in this disease? How can EU legislation help to control the outbreak?


He explains how climate change is actually a factor influencing the increase of susceptible crops, alongside multiple other influences – yet there are only “tentative explanations” for the speed of change in late blight. Latin America, Eastern Asia and Eastern sub-Saharan Africa have seen emergence of a mutated late blight, showing the unpredictability of the disease.


With global food production needed to increase by 70% by 2050, handling this global threat is at the forefront of agricultural minds.


Here, Phil Hogan, former European Commissioner for Agriculture, describes the priorities of the EU Common Agricultural Policy (CAP) in relation to sustainability and disease. He details encouraging figures, such as €365 billion being poured into CAP. This significant sum could protect 96% of every euro paid to farmers from 2014-2019, up until 2027. Another substantial focus for the EU is research: prioritising food, agriculture, rural development and bioeconomy, which is set to receive €10 billion.


To learn about the hard science behind potato late blight, the exact legislative proposals in the EU and what should happen next for agriculture, read what Didier Andrivon has to say.

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bioRxiv: Optimizing the PBS1 Decoy System to Confer Resistance to Potyvirus Infection in Arabidopsis and Soybean (2020)

bioRxiv: Optimizing the PBS1 Decoy System to Confer Resistance to Potyvirus Infection in Arabidopsis and Soybean (2020) | Plants and Microbes | Scoop.it

The Arabidopsis resistance protein RPS5 is activated by proteolytic cleavage of the protein kinase PBS1 by the Pseudomonas syringae effector protease AvrPphB. We have previously shown that replacing seven amino acids at the cleavage site of PBS1 with a motif cleaved by the NIa protease of turnip mosaic virus (TuMV) enables RPS5 activation upon TuMV infection. However, this engineered resistance conferred a trailing necrosis phenotype indicative of a cell death response too slow to contain the virus. We theorized this could result from a positional mismatch within the cell between PBS1TuMV, RPS5 and the NIa protease. To test this, we re-localized PBS1TuMV and RPS5 to cellular sites of NIa accumulation. These experiments revealed that relocation of RPS5 away from the plasma membrane compromised RPS5-dependent cell death in N. benthamiana, even though PBS1 was efficiently cleaved. As an alternative approach, we tested whether overexpression of plasma membrane-localized PBS1TuMV would enhance RPS5 activation by TuMV. Significantly, over-expressing the PBS1TuMV decoy protein conferred complete resistance to TuMV when delivered by either Agrobacterium or by aphid transmission, showing that RPS5-mediated defense responses are effective against bacterial and viral pathogens. Lastly, we have now extended this PBS1 decoy approach to soybean by modifying a soybean PBS1 ortholog to be cleaved by the NIa protease of soybean mosaic virus (SMV). Transgenic overexpression of this soybean PBS1 decoy conferred immunity to SMV, demonstrating that we can use endogenous PBS1 proteins in crop plants to engineer economically relevant disease resistant traits.

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Tumblr: For the latest on plant-microbe interactions, you must check bioRxiv (2019)

Tumblr: For the latest on plant-microbe interactions, you must check bioRxiv (2019) | Plants and Microbes | Scoop.it

Some of the best work in the plant-microbe interactions field find its way on bioRxiv first. Check this amazing list of e-prints/preprints published just this last month on bioRxiv:

 

CRK2 and C-terminal phosphorylation of NADPH oxidase RBOHD regulate ROS production in Arabidopsis
Sachie Kimura, Kerri Hunter, Lauri Vaahtera, Huy Cuong Tran, Aleksia Vaattovaara, Anne Rokka, Sara Christina Stolze, Anne Harzen, Lena Meißner, Maya Wilkens, Thorsten Hamann, Masatsugu Toyota, Hirofumi Nakagami, Michael Wrzaczek
bioRxiv 618819; doi: https://doi.org/10.1101/618819

An N-terminal motif in NLR immune receptors is functionally conserved across distantly related plant species
Hiroaki Adachi, Mauricio Contreras, Adeline Harant, Chih-hang Wu, Lida Derevnina, Toshiyuki Sakai, Cian Duggan, Eleonora Moratto, Tolga O Bozkurt, Abbas Maqbool, Joe Win, Sophien Kamoun
bioRxiv 693291; doi: https://doi.org/10.1101/693291

BSU1 family phosphatases mediate Flagellin-FLS2 signaling through a specific phosphocode
Chan Ho Park, Ji-Hyun Youn, Shou-Ling Xu, Jung-Gun Kim, Yang Bi, Nicole Xu, Mary Beth Mudgett, Seong-Ki Kim, Tae-Wuk Kim, Zhi-Yong Wang
bioRxiv 685610; doi: https://doi.org/10.1101/685610

Emergence of the Ug99 lineage of the wheat stem rust pathogen through somatic hybridisation
Feng Li, Narayana M. Upadhyaya, Jana Sperschneider, Oadi Matny, Hoa Nguyen-Phuc, Rohit Mago, Castle Raley, Marisa E. Miller, Kevin A.T. Silverstein, Eva Henningsen, Cory D. Hirsch, Botma Visser, Zacharias A. Pretorius, Brian J. Steffenson, Benjamin Schwessinger, Peter N. Dodds, Melania Figueroa
bioRxiv 692640; doi: https://doi.org/10.1101/692640

Effector prediction and characterization in the oomycete pathogen Bremia lactucae reveal host-recognized WY domain proteins that lack the canonical RXLR motif
Kelsey Wood, Munir Nur, Juliana Gil, Kyle Fletcher, Kim Lakeman, Ayumi Gothberg, Tina Khuu, Jennifer Kopetzky, Archana Pandya, Mathieu Pel, Richard Michelmore
bioRxiv 679787; doi: https://doi.org/10.1101/679787

Plant mixed lineage kinase domain-like proteins limit biotrophic pathogen growth
Lisa Mahdi, Menghang Huang, Xiaoxiao Zhang, Ryohei Thomas Nakano, Leïla Brulé Kopp, Isabel M.L. Saur, Florence Jacob, Viera Kovacova, Dmitry Lapin, Jane E. Parker, James M. Murphy, Kay Hofmann, Paul Schulze-Lefert, Jijie Chai, Takaki Maekawa
bioRxiv 681015; doi: https://doi.org/10.1101/681015

A generalist pathogen view of diverse host evolutionary histories through polygenic virulence
Celine Caseys, Gongjun Shi, Nicole Soltis, Raoni Gwinner, Jason Corwin, Susanna Atwell, Daniel Kliebenstein
bioRxiv 507491; doi: https://doi.org/10.1101/507491

Oligomerization of NLR immune receptor RPP7 triggered by atypical resistance protein RPW8/HR as ligand
Lei Li, Anette Habring, Kai Wang, Detlef Weigel
bioRxiv 682807; doi: https://doi.org/10.1101/682807

A receptor for herbivore-associated molecular patterns mediates plant immunity
Adam D. Steinbrenner, Maria Muñoz-Amatriaín, Jessica Montserrat Aguilar Venegas, Sassoum Lo, Da Shi, Nicholas Holton, Cyril Zipfel, Ruben Abagyan, Alisa Huffaker, Timothy J. Close, Eric A. Schmelz
bioRxiv 679803; doi: https://doi.org/10.1101/679803

Genome assembly and characterization of a complex zfBED-NLR gene-containing disease resistance locus in Carolina Gold Select rice with Nanopore sequencing
Andrew C. Read, Matthew J. Moscou, Aleksey V. Zimin, Geo Pertea, Rachel S. Meyer, Michael D. Purugganan, Jan E. Leach, Lindsay R. Triplett, Steven L. Salzberg, Adam J. Bogdanove
bioRxiv 675678; doi: https://doi.org/10.1101/675678

Improved control of Septoria tritici blotch in durum wheat using cultivar mixtures
S. Ben M’Barek, P. Karisto, M. Fakhfakh, H. Kouki, A. Mikaberidze, A. Yahyaoui
bioRxiv 664078; doi: https://doi.org/10.1101/664078

In-field detection and quantification of Septoria tritici blotch in diverse wheat germplasm using spectral-temporal features
Jonas Anderegg, Andreas Hund, Petteri Karisto, Alexey Mikaberidze
bioRxiv 664011; doi: https://doi.org/10.1101/664011

 

Follow the latest bioRxiv plant-microbe interactions papers on the biorxivTwitter feeds for Plant Biology, Microbiology and Genomics. You’ll also find some of the latest bioRxiv papers on the Scoop.it pages Plants and Microbesand  Plant Pathogenomics.

 

Learn more about preprints/e-prints at #ASAPbio.

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bioRxiv: An N-terminal motif in NLR immune receptors is functionally conserved across distantly related plant species (2019)

bioRxiv: An N-terminal motif in NLR immune receptors is functionally conserved across distantly related plant species (2019) | Plants and Microbes | Scoop.it

The molecular codes underpinning the functions of plant NLR immune receptors are poorly understood. We used in vitro Mu transposition to generate a random truncation library and identify the minimal functional region of NLRs. We applied this method to NRC4, a helper NLR that functions with multiple sensor NLRs within a Solanaceae receptor network. This revealed that the NRC4 N-terminal 29 amino acids are sufficient to induce hypersensitive cell death. This region is defined by the consensus MADAxVSFxVxKLxxLLxxEx (MADA motif) that is conserved at the N-termini of NRC family proteins and ~20% of coiled-coil (CC)-type plant NLRs. The MADA motif matches the N-terminal α1 helix of Arabidopsis NLR protein ZAR1, which undergoes a conformational switch during resistosome activation. Immunoassays revealed that the MADA motif is functionally conserved across NLRs from distantly related plant species. NRC-dependent sensor NLRs lack MADA sequences indicating that this motif has degenerated in sensor NLRs over evolutionary time.


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Science: A global surveillance system for crop diseases (2019)

Science: A global surveillance system for crop diseases (2019) | Plants and Microbes | Scoop.it

To satisfy a growing demand for food, global agricultural production must increase by 70% by 2050. However, pests and crop diseases put global food supplies at risk. Worldwide, yield losses caused by pests and diseases are estimated to average 21.5% in wheat, 30.0% in rice, 22.6% in maize, 17.2% in potato, and 21.4% in soybean (1); these crops account for half of the global human calorie intake (2). Climate change and global trade drive the distribution, host range, and impact of plant diseases (3), many of which can spread or reemerge after having been under control (4). Though many national and regional plant protection organizations (NPPOs and RPPOs) work to monitor and contain crop disease outbreaks, many countries, particularly low-income countries (LICs), do not efficiently exchange information, delaying coordinated responses to prevent disease establishment and spread. To improve responses to unexpected crop disease spread, we propose a Global Surveillance System (GSS) that will extend and adapt established biosecurity practices and networking facilities into LICs, enabling countries and regions to quickly respond to emerging disease outbreaks to stabilize food supplies, enhancing global food protection.


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Current Opinion Plant Biology: NLR singletons, pairs, and networks: evolution, assembly, and regulation of the intracellular immunoreceptor circuitry of plants (2019)

Current Opinion Plant Biology: NLR singletons, pairs, and networks: evolution, assembly, and regulation of the intracellular immunoreceptor circuitry of plants (2019) | Plants and Microbes | Scoop.it

NLRs are modular plant and animal proteins that are intracellular sensors of pathogen-associated molecules. Upon pathogen perception, NLRs trigger a potent broad-spectrum immune reaction known as the hypersensitive response. An emerging paradigm is that plant NLR immune receptors form networks with varying degrees of complexity. NLRs may have evolved from multifunctional singleton receptors, which combine pathogen detection (sensor activity) and immune signalling (helper or executor activity) into a single protein, to functionally specialized interconnected receptor pairs and networks. In this article, we highlight some of the recent advances in plant NLR biology by discussing models of NLR evolution, NLR complex formation, and how NLR (mis)regulation modulates immunity and autoimmunity. Multidisciplinary approaches are required to dissect the evolution, assembly, and regulation of the immune receptor circuitry of plants. With the new conceptual framework provided by the elucidation of the structure and activation mechanism of a plant NLR resistosome, this field is entering an exciting era of research.


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Nature Plants: A resistosome-activated ‘death switch’ (2019)

Nature Plants: A resistosome-activated ‘death switch’ (2019) | Plants and Microbes | Scoop.it

Pathogen perception triggers a monomeric nucleotide-binding leucine-rich plant immune receptor to form a pentameric wheel-like complex termed a resistosome, with the N-terminal α helices forming a funnel-shaped structure that may perturb plasma membrane integrity to cause hypersensitive cell death.

 

Nucleotide-binding leucine-rich repeat (NLR) proteins are intracellular receptors that detect pathogen molecules and activate a robust immune response that includes the hypersensitive response (HR) cell death in plants1. Although plant NLRs are known to oligomerize through their N-terminal domains, such as the coiled coil (CC) domain2, the molecular mechanisms that underpin plant NLR activation and the subsequent execution of HR cell death have remained largely unknown. In two recent remarkable papers published in Science, Wang et al. have advanced our understanding of both the structural and biochemical bases of NLR activation in plants, creating a new conceptual framework. They reconstituted both the inactive and active complexes of the CC-NLR protein HOPZ-ACTIVATED RESISTANCE1 (ZAR1) with its partner receptor-like cytoplasmic kinases (RLCKs) and used cryo-electron microscopy to show that activated ZAR1 forms a structure called a resistosome — a wheel-like pentamer that can switch conformation to expose a funnel- shaped structure formed by the N-terminal α helices (α1) of the five CC domains. They propose a provocative model in which this funnel-like structure triggers HR cell death by translocating into the plasma membrane and perturbing membrane integrity, similar to pore-forming toxins.

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bioRxiv: Plasma membrane associated Receptor Like Kinases relocalise to plasmodesmata in response to osmotic stress (2019)

bioRxiv: Plasma membrane associated Receptor Like Kinases relocalise to plasmodesmata in response to osmotic stress (2019) | Plants and Microbes | Scoop.it

Plasmodesmata act as key elements in intercellular communication, coordinating processes related to plant growth, development and responses to environmental stresses. While many of the developmental, biotic and abiotic signals are primarily perceived at the plasma membrane (PM) by receptor proteins, plasmodesmata also cluster receptor-like activities and whether or not these two pathways interact is currently unknown. Here we show that specific PM located Leucine Rich Repeat Receptor Like Kinases (LRR RLKs), KIN7 and IMK2, which under optimal growth conditions are absented from plasmodesmata, rapidly relocate and cluster to the pores in response to osmotic stress. This process is remarkably fast, it is not a general feature of PM associated proteins and is independent of sterol and sphingolipid membrane composition. Focusing on KIN7, previously reported to be involved in stress responses, we show that relocalisation upon mannitol depends on KIN7 phosphorylation. Loss-of-function mutation in KIN7 induces delay in lateral root (LR) development and the mutant is affected in the root response to mannitol stress. Callose-mediated plasmodesmata regulation is known to regulate LR development. We found that callose levels are reduced in kin7 mutant background with a root phenotype resembling ectopic expression of PdBG1, an enzyme that degrades callose at the pores. Both the LR and callose phenotypes can be complemented by expression of KIN7 wild type and phosphomimic variants but not by KIN7 phosphodead mutant which fails to relocalise at plasmodesmata. Together the data indicate that re-organisation of RLKs to plasmodesmata is important for the regulation of callose and LR development as part of the plant response to osmotic stress.

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Science: Glycosidase and glycan polymorphism control hydrolytic release of immunogenic flagellin peptides (2019)

Science: Glycosidase and glycan polymorphism control hydrolytic release of immunogenic flagellin peptides (2019) | Plants and Microbes | Scoop.it

INTRODUCTION

Immunogenic flagellin fragments are a signature of bacterial invasion in both plants and animals. Plants recognize flagellin fragments via flagellin sensitive 2 (FLS2), a model receptor kinase that is highly conserved among angiosperms. However, little is known about events upstream of flagellin perception by FLS2. The flagellin fragments recognized by FLS2 are buried in the flagellin polymer structure and require hydrolytic release before recognition can occur, yet the hydrolases releasing these elicitors remain to be identified. Uncovering their identity is a daunting task because the extracellular space of plants (the apoplast) contains hundreds of uncharacterized glycosidases and proteases.

RATIONALE

We reasoned that pathogenic bacteria would suppress plant hydrolases that are important for immunity. To identify suppressed hydrolases in the apoplast of infected plants, we applied activity-based protein profiling with the use of chemical probes that irreversibly label the active site of hydrolases. We applied this strategy to study the infection of the tobacco relative Nicotiana benthamiana with the bacterial pathogens Pseudomonas syringae pv. tabaci(Pta6605), P. syringae pv. syringae (PsyB728a), and a virulent mutant of P. syringae pv. tomato[PtoDC3000(ΔhQ)].

RESULTS

Glycosidase activity profiling of apoplastic fluids isolated from PtoDC3000(ΔhQ)-infected plants revealed that the activity of β-galactosidase 1 (BGAL1) is suppressed in the apoplast during infection. BGAL1 suppression is caused by a heat-stable, basic, small inhibitor molecule that is produced by the bacteria under the control of hrpR/S/L virulence regulators. Null mutants of N. benthamiana lacking BGAL1 generated by genome editing have substantially reduced apoplastic β-galactosidase activity and are more susceptible to PtoDC3000(ΔhQ), demonstrating that BGAL1 contributes to immunity. When investigating how BGAL1 functions in immunity, we discovered that treatment of PtoDC3000(ΔhQ) and Pta6605 bacteria with apoplastic fluids containing BGAL1 results in the release of an elicitor that triggers a burst of reactive oxygen species in leaf discs, a signature immune response in plants. The released elicitor is flagellin derived because the triggered immune response requires both the FLS2 receptor in the plant and the flagellin-encoding fliC gene in the bacteria. More precisely, treatment of purified flagella with apoplastic fluids containing BGAL1 facilitates the release of immunogenic peptides from flagellin.

The flagellin polymer of both PtoDC3000(ΔhQ) and Pta6605 is O-glycosylated with glycans consisting of several rhamnose residues and a terminal modified viosamine (mVio). Mutant Pta6605 bacteria carrying nonglycosylated flagellin, or carrying rhamnosylated flagellin lacking mVio, trigger the plant immune response when treated with apoplastic fluids, irrespective of BGAL1 presence, thus demonstrating that BGAL1 requires mVio for its function in immunity. Addition of a protease inhibitor cocktail to apoplastic fluids blocks the release of the flagellin elicitor from nonglycosylated flagellin, implicating apoplastic proteases in elicitor release acting downstream of BGAL1. Consistent with a specific role of BGAL1 in elicitor release, bgal1 null mutants of N. benthamiana show increased susceptibility only to bacterial strains carrying mVio. Treatment of PsyB728a with apoplastic fluids containing BGAL1 does not facilitate release of the flagellin elicitor because its flagellin carries a different glycan moiety lacking mVio, thus providing protection against recognition.

CONCLUSION

Glycosidase BGAL1 acts upstream of proteases in the apoplast of N. benthamiana to release immunogenic peptides from glycosylated flagellin, but only on glycosylated flagellin containing mVio. P. syringae strains use both BGAL1 inhibitors and glycan polymorphism to suppress BGAL1 function and escape recognition. Glycan polymorphism is common to bacterial pathogens, indicating a general role for flagellin glycans in evading recognition of bacterial pathogens by both plants and animals.

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Zenodo: Death switch: how resistosomes activate immunity (2019)

Zenodo: Death switch: how resistosomes activate immunity (2019) | Plants and Microbes | Scoop.it

Pathogen perception triggers a monomeric NLR plant immune receptor to form a pentameric wheel-like complex termed a resistosome, with the N-terminal ahelices forming a funnel-shaped structure that may perturb plasma membrane integrity to cause hypersensitive cell death.

 

Nucleotide-binding leucine-rich repeat (NLR) proteins are intracellular receptors that detect pathogen molecules and activate a robust immune response that includes the hypersensitive response (HR) cell death in plants. Although plant NLRs are known to oilgomerize through their N-terminal domains, such as the coiled coil (CC) domain, the molecular mechanisms that underpin plant NLR activation and the subsequent execution of HR cell death have remained largely unknown. In two recent paradigm-shifting Science papers, Wang et al. have advanced our understanding of both the structural and biochemical bases of NLR activation in plants, creating a new conceptual framework. They reconstituted both the inactive and active complexes of the CC-NLR protein HOPZ-ACTIVATED RESISTANCE1 (ZAR1) with its partner receptor-like cytoplasmic kinases (RLCKs) and used cryo-electron microscopy to show that activated ZAR1 forms a resistosome—a wheel-like pentamer that can switch conformation to expose a funnel-shaped structure formed by the very N-terminal ahelices (a1) of the CC domains. They propose a provocative model in which the five exposeda1 helices of the ZAR1 resistosome form a funnel-like structurethat triggers HR cell death by translocating into the plasma membrane and perturbing membrane integrity similar to pore-forming toxins.

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bioRxiv: A bacterial effector protein prevents MAPK-mediated phosphorylation of SGT1 to suppress plant immunity (2020)

bioRxiv: A bacterial effector protein prevents MAPK-mediated phosphorylation of SGT1 to suppress plant immunity (2020) | Plants and Microbes | Scoop.it

Nucleotide-binding domain and leucine-rich repeat-containing (NLR) proteins function as sensors that perceive pathogen molecules and activate immunity. In plants, the accumulation and activation of NLRs is regulated by SUPPRESSOR OF G2 ALLELE OF skp1 (SGT1). In this work, we found that an effector protein named RipAC, secreted by the plant pathogen Ralstonia solanacearum, associates with SGT1 to suppress NLR-mediated SGT1-dependent immune responses, including those triggered by another R. solanacearum effector, RipE1. RipAC does not affect the accumulation of SGT1 or NLRs, or their interaction. However, RipAC inhibits the interaction between SGT1 and MAP kinases, and the phosphorylation of a MAPK target motif in the C-terminal domain of SGT1. Such phosphorylation is enhanced upon activation of immune signaling, leads to the release of the interaction between SGT1 and NLRs, and contributes to the activation of NLR-mediated responses. Additionally, SGT1 phosphorylation contributes to resistance against R. solanacearum, and this is particularly evident in the absence of RipAC. Our results shed light onto the mechanism of activation of NLR-mediated immunity, and suggest a positive feedback loop between MAPK activation and SGT1-dependent NLR activation.

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Nature Plants: Perception of Agrobacterium tumefaciens flagellin by FLS2 XL confers resistance to crown gall disease (2020)

Nature Plants: Perception of Agrobacterium tumefaciens flagellin by FLS2 XL confers resistance to crown gall disease (2020) | Plants and Microbes | Scoop.it

Bacterial flagella are perceived by the innate immune systems of plants1and animals2 alike, triggering resistance. Common to higher plants is the immunoreceptor FLAGELLIN-SENSING 2 (FLS2)3, which detects flagellin via its most conserved epitope, flg22. Agrobacterium tumefaciens, which causes crown gall disease in many crop plants, has a highly diverged flg22 epitope and evades immunodetection by plants so far studied. We asked whether, as a next step in this game of ‘hide and seek’, there are plant species that have evolved immunoreceptors with specificity for the camouflaged flg22Atum of A. tumefaciens. In the wild grape species Vitis riparia, we discovered FLS2XL, a previously unknown form of FLS2, that provides exquisite sensitivity to typical flg22 and to flg22Atum. As exemplified by ectopic expression in tobacco, FLS2XL can limit crown gall disease caused by A. tumefaciens.

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bioRxiv: Impact of a resistance gene against a fungal pathogen on the plant host residue microbiome: the case of the Leptosphaeria maculans-Brassica napus pathosystem (2020)

bioRxiv: Impact of a resistance gene against a fungal pathogen on the plant host residue microbiome: the case of the Leptosphaeria maculans-Brassica napus pathosystem (2020) | Plants and Microbes | Scoop.it

Oilseed rape residues are a crucial determinant of stem canker epidemiology, as they support the sexual reproduction of the fungal pathogen Leptosphaeria maculans. The aim of this study was to characterise the impact of a resistance gene against L. maculans infection on residue microbial communities and to identify micro-organisms interacting with this pathogen during residue degradation. We used near-isogenic lines to obtain healthy and infected host plants. The microbiome associated with the two types of plant residues was characterised by metabarcoding. A combination of linear discriminant analysis and ecological network analysis was used to compare the microbial communities and to identify micro-organisms interacting with L. maculans. Fungal community structure differed between the two lines at harvest, but not subsequently, suggesting that the presence/absence of the resistance gene influences the microbiome at the base of the stem whilst the plant is alive, but that this does not necessarily lead to differential colonisation of the residues by fungi. Direct interactions with other members of the community involved many fungal and bacterial ASVs (amplicon sequence variants). L. maculans appeared to play a minor role in networks, whereas one ASV affiliated to Plenodomus biglobosus (synonym Leptosphaeria biglobosa) from the Leptosphaeria species complex was considered a keystone taxon in the networks at harvest. This approach could be used to identify and promote micro-organisms with beneficial effects against residue-borne pathogens, and more broadly, to decipher the complex interactions between multi-species pathosystems and other microbial components in crop residues.

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Twitter: "I think we finally fixed the problems with #taxonomy of bacteria that cause #Xanthomonas Wilt on #banana and #enset and Bacterial Leaf Streak on #maize" (2020)

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Cell: A Bacterial Effector Mimics a Host HSP90 Client to Undermine Immunity (2019)

Cell: A Bacterial Effector Mimics a Host HSP90 Client to Undermine Immunity (2019) | Plants and Microbes | Scoop.it
• The bacterial effector HopBF1 adopts a minimal protein kinase fold
• HopBF1 phosphorylates and inactivates eukaryotic HSP90
• HopBF1 mimics an HSP90 client to achieve specificity
• HopBF1 is sufficient to induce disease symptoms in plants

The molecular chaperone HSP90 facilitates the folding of several client proteins, including innate immune receptors and protein kinases. HSP90 is an essential component of plant and animal immunity, yet pathogenic strategies that directly target the chaperone have not been described. Here, we identify the HopBF1 family of bacterial effectors as eukaryotic-specific HSP90 protein kinases. HopBF1 adopts a minimal protein kinase fold that is recognized by HSP90 as a host client. As a result, HopBF1 phosphorylates HSP90 to completely inhibit the chaperone’s ATPase activity. We demonstrate that phosphorylation of HSP90 prevents activation of immune receptors that trigger the hypersensitive response in plants. Consequently, HopBF1-dependent phosphorylation of HSP90 is sufficient to induce severe disease symptoms in plants infected with the bacterial pathogen, Pseudomonas syringae.Collectively, our results uncover a family of bacterial effector kinases with toxin-like properties and reveal a previously unrecognized betrayal mechanism by which bacterial pathogens modulate host immunity.

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bioRxiv: Improved control of Septoria tritici blotch in durum wheat using cultivar mixtures (2019)

bioRxiv: Improved control of Septoria tritici blotch in durum wheat using cultivar mixtures (2019) | Plants and Microbes | Scoop.it

Mixtures of cultivars with contrasting levels of disease resistance are capable of suppressing infectious diseases in wheat, as demonstrated in numerous field experiments. Most studies focused on airborne pathogens in bread wheat, while splash-dispersed pathogens have received less attention, and no studies have been conducted in durum wheat. We conducted a field experiment in Tunisia, a major durum wheat producer in the Mediterranean region, to evaluate the performance of cultivar mixtures in controlling the polycyclic, splash-dispersed disease Septoria tritici blotch (STB) in durum wheat. To measure STB severity, we used a novel, high-throughput method based on digital analysis of images captured from 1284 infected leaves collected from 42 experimental plots. This method allowed us to quantify pathogen reproduction on wheat leaves and to acquire a large dataset that exceeds previous studies with respect to accuracy and statistical power. Our analyses show that introducing only 25% of a disease-resistant cultivar into a pure stand of a susceptible cultivar provides a substantial reduction in disease -- down to the level of resistant pure stands -- and a corresponding mitigation of yield loss. However, adding a second resistant cultivar to the mixture did not further improve disease control, contrary to predictions of epidemiological theory. Susceptible cultivars are often agronomically superior to resistant cultivars. Hence, if mixtures with only a moderate proportion of the resistant cultivar provide similar degree of disease control as resistant pure stands, as our analysis indicates, such mixtures are more likely to be accepted by growers.

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Zenodo: A clone resource of Magnaporthe oryzae effectors that share sequence and structural similarities across host-specific lineages (2019)

Zenodo: A clone resource of Magnaporthe oryzae effectors that share sequence and structural similarities across host-specific lineages (2019) | Plants and Microbes | Scoop.it

We describe a clone resource of 195 effectors of the blast fungus Magnaporthe oryzae. These clones are freely available as Golden Gate compatible entry plasmids. Our aim is to provide the community with an open source effector clone library to be used in a variety of functional studies.

 

Plant pathogens secrete effectors that play central roles in subjugating plants for colonization. Effectors typically have signal peptides, and occasionally carry conserved folds and motifs (Lo Presti et al.,2015; Franceschettiet al., 2017). Magnaporthe oryzae(Syn. Pyricularia oryzae) is an important plant pathogenthat is able to infect around 50 species of both wild and cultivated grasses including important cereals of the Poaceae family. M. oryzaeis mostly known to cause rice blast but can also cause disease on other crops such as barley, wheat, foxtail millet, and finger millet. The global population of Magnaporthe is composed of genetically differentiated lineages which, in some cases, still exhibit a measurable degree of gene flow (Gladieux et al.,2018). Fungal isolates from each of those lineages show a preference for a specific host and also encode distinct repertoires of effector genes (Yoshida et al.,2016). 

 

The first genomic sequence of Magnaporthe oryzaewas released in 2005 for the lab strain 70-15 and allowed to predict a large set of secreted proteins such as enzymes involved in secondary metabolism and virulence-associated factors including putative effectors (Dean et al.,2005). Recently an increasing number of genome sequences of isolates from different lineages have become available, allowing the research community to perform comparative genomic studies (Chiapello et al.,2015; Yoshida et al.,2016). 

 

Many of the validated effectors of M. oryzae are known as the MAX (MagnaportheAVRs and ToxB like) effectors. These effectors, while showing little primary sequence similarity, share a conserved structural fold composed of 6 β-sheets alternating in an anti-parallel manner (de Guillenet al., 2015). The MAX family has been largely expanded in Magnaportheas those effectors account for 5-10% of the effector repertoire and for 50% of the already cloned effectors of Magnaporthe(de Guillenet al., 2015). Indeed, the identification of structural motifs enables more sensitive predictions of effectors from pathogen genomes compared to sequence similarity searches (Franceschettiet al., 2017).

 

The aim of this project was to computationally identify a set of M. oryzaeeffectors from the main host-specific lineages and develop an open access clone resource for functional analyses.

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PLOS Biology: Plant health emergencies demand open science: Tackling a cereal killer on the run (2019)

PLOS Biology: Plant health emergencies demand open science: Tackling a cereal killer on the run (2019) | Plants and Microbes | Scoop.it

In this Perspective article, the authors share their personal experience with the appearance in Bangladesh of a destructive new fungal disease called wheat blast and stress the importance of open science platforms and crowdsourced community responses in tackling emerging plant diseases.


Via The Sainsbury Lab, Kamoun Lab @ TSL
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Current Biology: The £15 billion cost of ash dieback in Britain (2019)

Current Biology: The £15 billion cost of ash dieback in Britain (2019) | Plants and Microbes | Scoop.it

Invasive tree pests and diseases present some of the greatest global threats to forests, and the recent global acceleration in invasions has caused massive ecological damage. Calls to improve biosecurity have, however, often lost out to economic arguments in favour of trade. Human activities, such as trade, move organisms between continents, and interventions to reduce risk of introductions inevitably incur financial costs. No previous studies have attempted to estimate the full economic cost of a tree disease, and the economic imperative to improve biosecurity may have been underappreciated. We set out to estimate the cost of the dieback of ash, Fraxinus excelsior, caused by Hymenoscyphus fraxineus, in Great Britain, and investigate whether this may be the case.

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bioRxiv: Chitin perception in plasmodesmata identifies subcellular, context-specific immune signalling in plants (2019)

bioRxiv: Chitin perception in plasmodesmata identifies subcellular, context-specific immune signalling in plants (2019) | Plants and Microbes | Scoop.it

The plasma membrane (PM) that lines plasmodesmata has a distinct protein and lipid composition, underpinning specific regulation of these connections between cells. The plasmodesmal PM can integrate extracellular signals differently from the cellular PM, but it is not known how this specificity is established or how a single stimulus can trigger independent signalling cascades in neighbouring membrane domains. Here we have used the fungal elicitor chitin to investigate signal integration and responses at the plasmodesmal PM. We found that the plasmodesmal PM employs a receptor complex composed of the LysM receptors LYM2 and LYK4 which respectively change their location and interactions in response to chitin. Downstream, signalling is transmitted via a specific phosphorylation signature of an NADPH oxidase and localised callose synthesis that causes plasmodesmata closure. This demonstrates the plasmodesmal PM deploys both plasmodesmata-specific components and differential activation of PM-common components to independently integrate an immune signal.

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bioRxiv: Protein engineering expands the effector recognition profile of a rice NLR immune receptor (21019)

bioRxiv: Protein engineering expands the effector recognition profile of a rice NLR immune receptor (21019) | Plants and Microbes | Scoop.it

Plant NLR receptors detect pathogen effectors and initiate an immune response. Since their discovery, NLRs have been the focus of protein engineering to improve disease resistance. However, this has proven challenging, in part due to their narrow response specificity. Here, we used structure-guided engineering to expand the response profile of the rice NLR Pikp to variants of the rice blast pathogen effector AVR-Pik. A mutation located within an effector binding interface of the integrated Pikp-HMA domain increased the binding affinity for AVR-Pik variants in vitro and in vivo. This translates to an expanded cell death response to AVR-Pik variants previously unrecognized by Pikp in planta. Structures of the engineered Pikp-HMA in complex with AVR-Pik variants revealed the mechanism of expanded recognition. These results provide a proof-of-concept that protein engineering can improve the utility of plant NLR receptors where direct interaction between effectors and NLRs is established, particularly via integrated domains.

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PNAS: Biosynthesis and secretion of the microbial sulfated peptide RaxX and binding to the rice XA21 immune receptor (2019)

PNAS: Biosynthesis and secretion of the microbial sulfated peptide RaxX and binding to the rice XA21 immune receptor (2019) | Plants and Microbes | Scoop.it

The rice immune receptor XA21 is activated by the sulfated microbial peptide required for activation of XA21-mediated immunity X (RaxX) produced by Xanthomonas oryzae pv. oryzae (Xoo). Mutational studies and targeted proteomics revealed that the RaxX precursor peptide (proRaxX) is processed and secreted by the protease/transporter RaxB, the function of which can be partially fulfilled by a noncognate peptidase-containing transporter component B (PctB). proRaxX is cleaved at a Gly–Gly motif, yielding a mature peptide that retains the necessary elements for RaxX function as an immunogen and host peptide hormone mimic. These results indicate that RaxX is a prokaryotic member of a previously unclassified and understudied group of eukaryotic tyrosine sulfated ribosomally synthesized, posttranslationally modified peptides (RiPPs). We further demonstrate that sulfated RaxX directly binds XA21 with high affinity. This work reveals a complete, previously uncharacterized biological process: bacterial RiPP biosynthesis, secretion, binding to a eukaryotic receptor, and triggering of a robust host immune response.

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