Plants and Microbes
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Day 3 Updates of #OMGN12 Oomycete Molecular Genetics Network Annual Meeting, Nanjing, China

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Kamoun Lab @ TSL's comment, May 28, 2012 5:09 AM
That's it! Thanks to Yuanchao Wang and colleagues for organizing a great meeting. See you all next year at #OMGN13 in Asilomar... and remember 2014 in Norwich in late June or early July just before the IC-MPMI Congress in Rhodes, Greece.
Gmail.com's comment, May 28, 2012 6:42 AM
Thanks for all the posts, especially to Sophian. it has been a great update for those who could not make it. I have been reading all of them.

Kamoun Lab @ TSL's comment, May 28, 2012 9:35 AM
Several asked me for the link to my talk "Don't Perish: Step-by-step guide to writing scientific papers". Here it is: http://t.co/hvstUQSP
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Nature Plants: Polymorphic residues in rice NLRs expand binding and response to effectors of the blast pathogen (2018)

Nature Plants: Polymorphic residues in rice NLRs expand binding and response to effectors of the blast pathogen (2018) | Plants and Microbes | Scoop.it

Accelerated adaptive evolution is a hallmark of plant–pathogen interactions. Plant intracellular immune receptors (NLRs) often occur as allelic series with differential pathogen specificities. The determinants of this specificity remain largely unknown. Here, we unravelled the biophysical and structural basis of expanded specificity in the allelic rice NLR Pik, which responds to the effector AVR-Pik from the rice blast pathogen Magnaporthe oryzae. Rice plants expressing the Pikm allele resist infection by blast strains expressing any of three AVR-Pik effector variants, whereas those expressing Pikp only respond to one. Unlike Pikp, the integrated heavy metal-associated (HMA) domain of Pikm binds with high affinity to each of the three recognized effector variants, and variation at binding interfaces between effectors and Pikp-HMA or Pikm-HMA domains encodes specificity. By understanding how co-evolution has shaped the response profile of an allelic NLR, we highlight how natural selection drove the emergence of new receptor specificities. This work has implications for the engineering of NLRs with improved utility in agriculture.


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bioRxiv: Tracking disease resistance deployment in potato breeding by enrichment sequencing (2018)

bioRxiv: Tracking disease resistance deployment in potato breeding by enrichment sequencing (2018) | Plants and Microbes | Scoop.it

Following the molecular characterisation of functional disease resistance genes in recent years, methods to track and verify the integrity of multiple genes in varieties are needed for crop improvement through resistance stacking. Diagnostic resistance gene enrichment sequencing (dRenSeq) enables the high-confidence identification and complete sequence validation of known functional resistance genes in crops. As demonstrated for tetraploid potato varieties, the methodology is more robust and cost-effective in monitoring resistances than whole-genome sequencing and can be used to appraise (trans)gene integrity efficiently. All currently known NB-LRRs effective against viruses, nematodes and the late blight pathogen Phytophthora infestans can be tracked with dRenSeq in potato and hitherto unknown polymorphisms have been identified. The methodology provides a means to improve the speed and efficiency of future disease resistance breeding in crops by directing parental and progeny selection towards effective combinations of resistance genes.

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eLife: Host autophagy machinery is diverted to the pathogen interface to mediate focal defense responses against the Irish potato famine pathogen (2018)

eLife: Host autophagy machinery is diverted to the pathogen interface to mediate focal defense responses against the Irish potato famine pathogen (2018) | Plants and Microbes | Scoop.it

During plant cell invasion, the oomycete Phytophthora infestans remains enveloped by host-derived membranes whose functional properties are poorly understood. P. infestans secretes a myriad of effector proteins through these interfaces for plant colonization. Recently we showed that the effector protein PexRD54 reprograms host-selective autophagy by antagonising antimicrobial-autophagy receptor Joka2/NBR1 for ATG8CL binding (Dagdas, 2016). Here, we show that during infection, ATG8CL/Joka2 labelled defense-related autophagosomes are diverted toward the perimicrobial host membrane to restrict pathogen growth. PexRD54 also localizes to autophagosomes across the perimicrobial membrane, consistent with the view that the pathogen remodels host-microbe interface by co-opting the host autophagy machinery. Furthermore, we show that the host-pathogen interface is a hotspot for autophagosome biogenesis. Notably, overexpression of the early autophagosome biogenesis protein ATG9 enhances plant immunity. Our results implicate selective autophagy in polarized immune responses of plants and point to more complex functions for autophagy than the widely known degradative roles.

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Molecular Plant Pathology: Resistance to phytopathogens e tutti quanti: placing plant quantitative disease resistance on the map ( 2014)

Molecular Plant Pathology: Resistance to phytopathogens e tutti quanti: placing plant quantitative disease resistance on the map ( 2014) | Plants and Microbes | Scoop.it

Plant disease resistance can be seen as a process of a dual nature: both qualitative and quantitative. The nature of non-self molecules perceived by plants has led to the depiction of plant immunity as a two-layer defence system. The first layer is mediated by cell surface and intracellular pattern recognition receptors (PRRs) which perceive conserved microbial elicitors, termed pathogen- associated molecular patterns (PAMPs). The perception of these conserved elicitors initiates cascades of signalling and transcrip- tion events, known as PAMP-triggered immunity (PTI). Adapted pathogens secrete effector molecules able to suppress PTI, but which may also be recognized by plant intracellular resistance (R) proteins. This initiates effector-triggered immunity (ETI), the second layer of plant defence. ETI typically yields complete disease resistance phenotypes against pathogens containing the recog- nized effector, a process designated as qualitative resistance. By contrast, perception of a single PAMP typically has a weaker contribution to overall plant resistance. More generally, in the absence of qualitative resistance, an incomplete resistance phe- nomenon is often observed, leading to a reduction rather than absence of disease. This is usually referred to as quantitative disease resistance (QDR).

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YouTube: Plants have an immune system… and it’s complicated (2018)

Just like humans, plants have an immune system that they use to fend off pathogens and pests. Research involving plant immunity was guided by Harold Flor’s influential “gene-for-gene” model but this model is now supplanted by a more complex view of pant immunity. Disease resistance genes appear to work together in intricate networks that enable plants to detect and resist parasites more effectively. An in-depth understanding of the immune system can help us breed disease resistant crops.

 

Chih-Hang Wu, Lida Derevnina, Sophien Kamoun. 2018. Receptor networks underpin plant immunity. Science, 360:1300-1301.

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Plant Cell: Receptor-like Cytoplasmic Kinases Directly Link Diverse Pattern Recognition Receptors to the Activation of Mitogen-activated Protein Kinase Cascades in Arabidopsis (2018)

Plant Cell: Receptor-like Cytoplasmic Kinases Directly Link Diverse Pattern Recognition Receptors to the Activation of Mitogen-activated Protein Kinase Cascades in Arabidopsis (2018) | Plants and Microbes | Scoop.it
Plants deploy numerous cell surface-localized pattern-recognition receptors (PRRs) to perceive host- and microbe-derived molecular patterns that are specifically released during infection and activate defense responses. The activation of the mitogen-activated protein kinases MPK3, MPK4 and MPK6 (MPK¾/6) is a hallmark of immune system activation by all known PRRs and is crucial for establishing disease resistance. The MAP kinase kinase kinase (MAPKKK) MEKK1 controls MPK4 activation, but the MAPKKKs responsible for MPK3/6 activation downstream of diverse PRRs and how the perception of diverse molecular patterns leads to the activation of MAPKKKs remain elusive. Here we show that two highly related MAPKKKs, MAPKKK3 and MAPKKK5, mediate MPK3/6 activation by at least four PRRs and confer resistance to bacterial and fungal pathogens in Arabidopsis thaliana. The receptor-like cytoplasmic kinases VII (RLCK VII), which act downstream of PRRs, directly phosphorylate MAPKKK5 Ser599, which is required for pattern-triggered MPK3/6 activation, defense gene expression, and disease resistance. Surprisingly, MPK6 further phosphorylates MAPKKK5 Ser682 and Ser692 to enhance MPK3/6 activation and disease resistance, pointing to a positive feedback mechanism. Finally, MEKK1 Ser603 is phosphorylated by both RLCK VII and MPK4, which is required for pattern-triggered MPK4 activation. These findings illustrate central mechanisms by which multiple PRRs activate MAPK cascades and disease resistance.

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Studies in Mycology: Two different R gene loci co-evolved with Avr2 of Phytophthora infestans and confer distinct resistance specificities in potato (2018)

Studies in Mycology: Two different R gene loci co-evolved with Avr2 of Phytophthora infestans and confer distinct resistance specificities in potato (2018) | Plants and Microbes | Scoop.it

Late blight, caused by the oomycete pathogen Phytophthora infestans, is the most devastating disease in potato. For sustainable management of this economically important disease, resistance breeding relies on the availability of resistance (R) genes. Such R genes against P. infestans have evolved in wild tuber-bearing Solanum species from North, Central and South America, upon co-evolution with cognate avirulence (Avr) genes. Here, we report how effectoromics screens with Avr2 of P. infestans revealed defense responses in diverse Solanum species that are native to Mexico and Peru. We found that the response to AVR2 in the Mexican Solanum species is mediated by R genes of the R2 family that resides on a major late blight locus on chromosome IV. In contrast, the response to AVR2 in Peruvian Solanum species is mediated by Rpi-mcq1, which resides on chromosome IX and does not belong to the R2 family. The data indicate that AVR2 recognition has evolved independently on two genetic loci in Mexican and Peruvian Solanum species, respectively. Detached leaf tests on potato cultivar ‘Désirée’ transformed with R genes from either the R2 or the Rpi-mcq1 locus revealed an overlapping, but distinct resistance profile to a panel of 18 diverse P. infestans isolates. The achieved insights in the molecular R – Avr gene interaction can lead to more educated exploitation of R genes and maximize the potential of generating more broad-spectrum, and potentially more durable control of the late blight disease in potato.


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Science: Plants send small RNAs in extracellular vesicles to fungal pathogen to silence virulence genes (2018)

Science: Plants send small RNAs in extracellular vesicles to fungal pathogen to silence virulence genes (2018) | Plants and Microbes | Scoop.it

Some pathogens and pests deliver small RNAs (sRNAs) into host cells to suppress host immunity. Conversely, hosts also transfer sRNAs into pathogens and pests to inhibit their virulence. Although sRNA trafficking has been observed in a wide variety of interactions, how sRNAs are transferred, especially from hosts to pathogens/pests, is still unknown. Here we show that host Arabidopsis cells secrete exosome-like extracellular vesicles to deliver sRNAs into fungal pathogen Botrytis cinerea. These sRNA-containing vesicles accumulate at the infection sites and are taken up by the fungal cells. Transferred host sRNAs induce silencing of fungal genes critical for pathogenicity. Thus, Arabidopsis has adapted exosome-mediated cross-kingdom RNA interference as part of its immune responses during the evolutionary arms race with the pathogen.

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mBio: The Blast Fungus Decoded: Genomes in Flux (2018)

mBio: The Blast Fungus Decoded: Genomes in Flux (2018) | Plants and Microbes | Scoop.it

Plant disease outbreaks caused by fungi are a chronic threat to global food security. A prime case is blast disease, which is caused by the ascomycete fungus Magnaporthe oryzae (syn. Pyricularia oryzae), which is infamous as the most destructive disease of the staple crop rice. However, despite its Linnaean binomial name, M. oryzae is a multihost pathogen that infects more than 50 species of grasses. A timely study by P. Gladieux and colleagues (mBio 9:e01219-17, 2018, https://doi.org/10.1128/mBio.01219-17) reports the most extensive population genomic analysis of the blast fungus thus far. M. oryzae consists of an assemblage of differentiated lineages that tend to be associated with particular host genera. Nonetheless, there is clear evidence of gene flow between lineages consistent with maintaining M. oryzae as a single species. Here, we discuss these findings with an emphasis on the ecologic and genetic mechanisms underpinning gene flow. This work also bears practical implications for diagnostics, surveillance, and management of blast diseases.

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bioRxiv: BED-domain containing immune receptors confer diverse resistance spectra to yellow rust (2018)

bioRxiv: BED-domain containing immune receptors confer diverse resistance spectra to yellow rust (2018) | Plants and Microbes | Scoop.it

Crop diseases reduce wheat yields by ~25% globally and thus pose a major threat to global food security. Genetic resistance can reduce crop losses in the field and can be selected for through the use of molecular markers. However, genetic resistance often breaks down following changes in pathogen virulence, as experienced with the wheat yellow (stripe) rust fungus Puccinia striiformis f. sp. tritici (PST). This highlights the need to (i) identify genes that alone or in combination provide broad-spectrum resistance and (ii) increase our understanding of the underlying molecular mode of action. Here we report the isolation and characterisation of three major yellow rust resistance genes (Yr7, Yr5, and YrSP) from hexaploid wheat (Triticum aestivum), each having a distinct and unique recognition specificity. We show that Yr5, which remains effective to a broad range of PST isolates worldwide, is allelic to YrSP and paralogous to Yr7, both of which have been overcome by multiple PST isolates. All three Yr genes belong to a complex resistance gene cluster on chromosome 2B encoding nucleotide-binding and leucine-rich repeat proteins (NLRs) with a non-canonical N-terminal zinc-finger BED domain that is distinct from those found in non-NLR wheat proteins. We developed and tested diagnostic markers to accelerate haplotype analysis and for marker-assisted selection to enable the stacking of the non-allelic Yr genes. Our results provide evidence that the BED-NLR gene architecture can provide effective field-based resistance to important fungal diseases such as wheat yellow rust.

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bioRxiv: NRG1 is required for the function of the TIR-NLR immune receptors Roq1 and RPP1 in Nicotiana benthamiana (2018)

bioRxiv: NRG1 is required for the function of the TIR-NLR immune receptors Roq1 and RPP1 in Nicotiana benthamiana (2018) | Plants and Microbes | Scoop.it

The plant immune system involves a large family of nucleotide-binding leucine-rich repeat (NLR) intracellular immune receptors. These immune receptors often function to directly or indirectly mediate the perception of specific pathogen effector proteins secreted into the cell. Activation of these immune receptors typically results in activation of the immune system and subsequent suppression of pathogen proliferation. Although many examples of NLR receptors are known, a mechanistic understanding of how receptor activation ultimately leads to an immune response is not well understood. A subset of the NLR proteins contain a TIR domain at their N terminus (TNL). One such TNL, the N gene, was previously shown to depend on a non-TIR NLR protein, N requirement gene 1 (NRG1) for immune function. We tested additional NLR proteins in Nicotiana benthamiana for dependency on NRG1. We found that two additional TIR-NLR proteins, Roq1 and RPP1, also require NRG1 but that two coiled-coil NLR proteins, Bs2 and Rps2, do not. This finding suggests that NRG1 may be a conserved component of TNL signaling pathways.

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Libération: Semences autochtones : la Tunisie en prend de la graine / Native Seeds: Tunisia Takes Lesson (2018)

Libération: Semences autochtones : la Tunisie en prend de la graine / Native Seeds: Tunisia Takes Lesson (2018) | Plants and Microbes | Scoop.it

[English translation]

 

While improved wheat seeds, massively imported in the 1980s, are caught up by diseases, traditional varieties are resisting.

Wearing a wool sweater, eyes narrowed by the wind, Nabil Ben Marzouk contemplates his army: one hectare of "chili", indigenous seed of durum wheat, lost in the middle of Mount Lansarine at some 360 meters altitude and 60 kilometers west of Tunis. He does not cultivate the "karim", the so-called improved high yield variety, because created in Mexico, in a laboratory of the International Center for Improvement of Corn and Wheat (Cimmyt). At the beginning of the 1980s, in the middle of a green revolution, the Tunisian authorities favored the establishment of karim for the production of couscous and pasta. The National Institute of Agricultural Research of Tunisia (INRAT) estimated in 2016 that karim represented 40% of the land sown to durum wheat.

 

"Biskri, mahmoudi [other indigenous varieties], chili symbolize both Tunisia and the flag. Nobody would dare make our colors disappear. But that's exactly what happens with our wheat, "says Nabil Marzouk. The sixty-year-old remembers when, as a child, his father and the other grain men brought donkey sacks of harvested wheat back to the immobilized combine because they could not get on the steep fields. If he cannot win this war, Nabil Ben Marzouk, whose left arm sports a valiant tattoo "I continue", resists. With eight other local farmers, he created an association, Amazir, which produces over ten hectares of semolina and bulgur from ancestral seeds and sold to Italy.

 

Falling yields

 

As time passes, improved varieties such as karim are less and less resistant to fungal diseases (rust and septoria), which can reduce production by 20-40%. They are also struggling to adapt to more and more frequent droughts. The vast majority of the 850 000 hectares of durum wheat is not irrigated. As a result, in bad years, karim yields drop to 5 quintals (500 kg) per hectare, compared to 40 to 60 on average. "Me, I always make 15 quintals per hectare whatever the hazards and without additional water, pesticide or herbicide", prides Nabil Ben Marzouk.

 

Aware of the benefits of indigenous varieties, the National Genebank (BNG), which is responsible for the conservation of the genetic diversity of the agricultural heritage, launched in 2010 an in situ culture program. Producers are offered a bag of 50 kilos of native seed. In exchange, they promise to return the same amount at the end of the harvest. In 2012, the institution received more than 132,000 euros from FAO, the UN's Food and Agriculture Organization, to develop this project. Some 81 farmers are currently cultivating 38 traditional seeds, covering an area of 100 hectares.

 

Enhancement

 

"I was surprised to see cereal farmers so receptive. Some remembered their father who used these seeds, others had lost a lot after a bad harvest and they were curious to try them, "says Amine Slim, program manager at the BNG, who benefits from his field visits to find ancient varieties that remain unknown. Many farmers continue to grow traditional varieties for home consumption. "When Amine came to see us, we did not need his bags," recalls Nabil Ben Marzouk. We gave him our seeds so he can keep them. "

 

Thanks to this approach, the NBG has seen, among other things, that indigenous wheat semolina has a better protein content than that of improved varieties, 17% compared to 12% on average. The original varieties also produce more straw, which is used to feed livestock or is resold in the form of boots. But these specificities are not recognized by the National Office of Cereals, the main outlet for producers, who buys the crops at a fixed price, 25.40 euros the quintal. Aboriginal durum would sell twice as much among connoisseurs and export if such an industry were developed.

 

At the Ministry of Agriculture, the goal remains self-sufficiency - current production reaches 70% of needs - leaving little room for “chili” and its sisters. "This is a niche production that could be encouraged by establishing a separate subsidiary, which would add premium to the selling price," says Mohamed Ali Ben Romdhane, deputy director of cereals at the Directorate General of Agricultural Production. But farmers need to first come together to be identified.

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Current Opinion Plant Biology: Extracellular vesicles as key mediators of plant–microbe interactions (2018)

Current Opinion Plant Biology: Extracellular vesicles as key mediators of plant–microbe interactions (2018) | Plants and Microbes | Scoop.it
• Plants produce extracellular vesicles (EVs) in response to infection.
• Recent advances in EV purification are now revealing the contents of plant EVs.
• Plant EVs are enriched in stress-response proteins and signaling lipids.
• EVs contain transporters for antimicrobial compounds such as glucosinolates.
• Indirect evidence suggests that EVs may mediate inter-kingdom RNA interference.

Extracellular vesicles (EVs) are lipid compartments capable of trafficking proteins, lipids, RNA and metabolites between cells. Plant cells have been shown to secrete EVs during immune responses, but virtually nothing is known about their formation, contents or ultimate function. Recently developed methods for isolating plant EVs have revealed that these EVs are enriched in stress response proteins and signaling lipids, and appear to display antifungal activity. Comparison to work on animal EVs, and the observation that host-derived small interfering RNAs and microRNAs can silence fungal genes, suggests that plant EVs may also mediate trans-kingdom RNA interference. Many fundamental questions remain, however, regarding how plant EVs are produced, how they move, and if and how they are taken up by target cells.

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Annual Reviews of Phytopathology: CRISPR Crops: Plant Genome Editing Toward Disease Resistance (2018)

Annual Reviews of Phytopathology: CRISPR Crops: Plant Genome Editing Toward Disease Resistance (2018) | Plants and Microbes | Scoop.it

Genome editing by sequence-specific nucleases (SSNs) has revolutionized biology by enabling targeted modifications of genomes. Although routine plant genome editing emerged only a few years ago, we are already witnessing the first applications to improve disease resistance. In particular, CRISPR-Cas9 has democratized the use of genome editing in plants thanks to the ease and robustness of this method. Here, we review the recent developments in plant genome editing and its application to enhancing disease resistance against plant pathogens. In the future, bioedited disease resistant crops will become a standard tool in plant breeding.


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bioRxiv: CRISPR-Cas9 ribonucleoprotein-mediated co-editing and counterselection in the rice blast fungus (2018)

bioRxiv: CRISPR-Cas9 ribonucleoprotein-mediated co-editing and counterselection in the rice blast fungus (2018) | Plants and Microbes | Scoop.it

The rice blast fungus Magnaporthe oryzae is the most serious pathogen of cultivated rice and a significant threat to global food security. To accelerate targeted mutation and specific gene editing in this species, we have developed a rapid plasmid-free CRISPR-Cas9-based gene editing method. It has previously been reported in M. oryzae that transformation with plasmids expressing Cas9 can generate specific mutations using sgRNAs, directing the endonuclease to specific genes. We show, however, that expression of Cas9 is highly toxic to M. oryzae, rendering this approach impractical. We demonstrate that using purified Cas9 pre-complexed to RNA guides to form ribonucleoproteins (RNPs), provides an alternative and very effective gene editing procedure. When used in combination with oligonucleotide or PCR-generated donor DNAs, generation of strains with specific base pair edits, in-locus gene replacements, or multiple gene edits, is very rapid and straightforward. Additionally, we report a novel counterselection strategy which allows creation of precisely edited fungal strains that contain no foreign DNA and are completely isogenic to the wild type. Together, these developments represent a scalable improvement in the precision and speed of genetic manipulation in M. oryzae and are likely to be broadly applicable to other fungal species.

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bioRxiv: TTL proteins scaffold brassinosteroid signaling components at the plasma membrane to optimize signal transduction in plant cells (2018)

bioRxiv: TTL proteins scaffold brassinosteroid signaling components at the plasma membrane to optimize signal transduction in plant cells (2018) | Plants and Microbes | Scoop.it

Brassinosteroids (BRs) form a group of steroidal hormones essential for plant growth, development and stress responses. Here, we report that plant-specific TETRATRICOPEPTIDE THIOREDOXIN-LIKE (TTL) proteins are positive regulators of BR signaling functioning as scaffold for BR signaling components in Arabidopsis. TTL3 forms a complex with all core components involved in BR signaling, including the receptor kinase BRASSINOSTEROID INSENSITIVE1 (BRI1), the transcription factor BRASSINAZOLE RESISTANT1 (BZR1) and the phosphatase BRI1-SUPPRESSOR1 (BSU1), but excluding the co-receptor BAK1. TTL3 is mainly localized in the cytoplasm, but BR treatment increases its localization at the plasma membrane, where it strengthens the association with BR signaling components. Consistent with a role in BR signaling, mutations in TTL3 and related TTL1 and TTL4 genes cause reduced BR responsiveness. We propose a mechanistic model for BR signaling, in which cytoplasmic/nuclear BR components bound to TTL proteins are recruited to the plasma membrane upon BR perception, which in turn allows the assembly of a BR signaling complex, leading to the de-phosphorylation and nuclear accumulation of the transcription factors BZR1 and BES1.


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Plant Journal: Advances on plant–pathogen interactions from molecular toward systems biology perspectives (2017)

Plant Journal: Advances on plant–pathogen interactions from molecular toward systems biology perspectives (2017) | Plants and Microbes | Scoop.it

In the past 2 decades, progress in molecular analyses of the plant immune system has revealed key elements of a complex response network. Current paradigms depict the interaction of pathogen‐secreted molecules with host target molecules leading to the activation of multiple plant response pathways. Further research will be required to fully understand how these responses are integrated in space and time, and exploit this knowledge in agriculture. In this review, we highlight systems biology as a promising approach to reveal properties of molecular plant–pathogen interactions and predict the outcome of such interactions. We first illustrate a few key concepts in plant immunity with a network and systems biology perspective. Next, we present some basic principles of systems biology and show how they allow integrating multiomics data and predict cell phenotypes. We identify challenges for systems biology of plant–pathogen interactions, including the reconstruction of multiscale mechanistic models and the connection of host and pathogen models. Finally, we outline studies on resistance durability through the robustness of immune system networks, the identification of trade‐offs between immunity and growth and in silico plant–pathogen co‐evolution as exciting perspectives in the field. We conclude that the development of sophisticated models of plant diseases incorporating plant, pathogen and climate properties represent a major challenge for agriculture in the future.

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Science: Receptor networks underpin plant immunity (2018)

Science: Receptor networks underpin plant immunity (2018) | Plants and Microbes | Scoop.it

Plants are attacked by a multitude of pathogens and pests, some of which cause epidemics that threaten food security. Yet a fundamental concept in plant pathology is that most plants are actively resistant to most pathogens and pests. Plants fend off their innumerable biotic foes primarily through innate immune receptors that detect the invading pathogens and trigger a robust immune response. The conceptual basis of such interactions was elegantly articulated by Harold H. Flor, who, in 1942, proposed the hypothesis that single genes in plants and pathogens define the outcome of their interactions; that is, a plant harboring a specific gene displays resistance against a pathogen that carries an interacting virulence gene (1). This gene-for-gene model was hugely insightful and influential—it has helped to guide applied and basic research on disease resistance. However, recent findings are taking the field beyond this simplified binary view of plant-pathogen interactions. Plants carry extremely diverse and dynamic repertoires of immune receptors that are interconnected in complex ways. Conversely, plant pathogens secrete a diversity of virulence proteins and metabolites called effectors, and pathogen genomics has revealed hundreds of effector genes in many species. These effectors have evidently evolved to favor pathogen infection and spread, but a subset of them inadvertently activate plant immune receptors. The emerging paradigm is that dynamic webs of genetic and biochemical networks underpin the early stages of plant-pathogen interactions.

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Cell Research: Plant G-protein activation: connecting to plant receptor kinases

Cell Research: Plant G-protein activation: connecting to plant receptor kinases | Plants and Microbes | Scoop.it

Plant heterotrimeric G-proteins function in important signaling pathways mediated by plant receptor kinases (RKs), however, the unique biochemical properties of Gα subunits have complicated our understanding of their regulation in plants. In their new paper in Cell Research, Liang et al. reveal that phosphorylation of the Gα regulator, RGS1, is critical for triggering G-protein signaling downstream of RK activation.


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Phytopathology: A new resistance gene in combination with Rmg8 confers strong resistance against Triticum isolates of Pyricularia oryzae in a common wheat landrace (2018)

Phytopathology: A new resistance gene in combination with Rmg8 confers strong resistance against Triticum isolates of Pyricularia oryzae in a common wheat landrace (2018) | Plants and Microbes | Scoop.it

The wheat blast fungus (Triticum pathotype of Pyricularia oryzae) first arose in Brazil in 1985 and has recently spread to Asia. Resistance genes against this new pathogen are very rare in common wheat populations. We screened 520 local landraces of common wheat collected worldwide with Br48, a Triticum isolate collected in Brazil, and found a highly resistant, unique accession, GR119. When F2 seedlings derived from a cross between GR119 and Chinese Spring (CS, susceptible control) were inoculated with Br48, resistant and susceptible seedlings segregated in a 15:1 ratio, suggesting that GR119 carries two resistance genes. When the F2 seedlings were inoculated with Br48△A8 carrying a disrupted allele of AVR-Rmg8 (an avirulence gene corresponding to a previously reported resistance gene, Rmg8), however, the segregation fitted a 3:1 ratio. These results suggest that one of the two genes in GR119 was Rmg8. The other, new gene was tentatively designated as RmgGR119. GR119 was highly resistant to all Triticum isolates tested. Spikes of GR119 were highly resistant to Br48, moderately resistant to Br48△A8 and a hybrid culture carrying avr-Rmg8 (nonfunctional allele), and highly resistant to its transformant carrying AVR-Rmg8. The strong resistance of GR119 was attributed to the combined effects of Rmg8 and RmgGR119.


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PLOS Biology: In vivo insertion pool sequencing identifies virulence factors in a complex fungal–host interaction (2018)

PLOS Biology: In vivo insertion pool sequencing identifies virulence factors in a complex fungal–host interaction (2018) | Plants and Microbes | Scoop.it

Large-scale insertional mutagenesis screens can be powerful genome-wide tools if they are streamlined with efficient downstream analysis, which is a serious bottleneck in complex biological systems. A major impediment to the success of next-generation sequencing (NGS)-based screens for virulence factors is that the genetic material of pathogens is often underrepresented within the eukaryotic host, making detection extremely challenging. We therefore established insertion Pool-Sequencing (iPool-Seq) on maize infected with the biotrophic fungus U. maydis. iPool-Seq features tagmentation, unique molecular barcodes, and affinity purification of pathogen insertion mutant DNA from in vivo-infected tissues. In a proof of concept using iPool-Seq, we identified 28 virulence factors, including 23 that were previously uncharacterized, from an initial pool of 195 candidate effector mutants. Because of its sensitivity and quantitative nature, iPool-Seq can be applied to any insertional mutagenesis library and is especially suitable for genetically complex setups like pooled infections of eukaryotic hosts.

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bioRxiv: Symbiosis-related genes sustain the development of a downy mildew pathogen on Arabidopsis thaliana (2018)

bioRxiv: Symbiosis-related genes sustain the development of a downy mildew pathogen on Arabidopsis thaliana (2018) | Plants and Microbes | Scoop.it

The interfaces through which nutrients are transferred from plant cells to arbuscular mycorrhiza fungi and biotrophic hyphal pathogens are structurally similar. We report that in Arabidopsis thaliana, mutations in homologs of common symbiosis genes (CSGs) encoding homologs of the symbiosis receptor kinase SYMRK, the nucleoporins NUP133 and SEC13 or the cation channel POLLUX reduce the reproductive success of Hyaloperonospora arabidopsidis (Hpa). Analysis of the multiplication of extracellular bacterial pathogens, Hpa-induced cell death or callose accumulation, as well as Hpa- or flg22-induced defence marker gene expression, did not reveal any traces of constitutive or exacerbated defence responses. We discovered an age-dependent, possibly senescence-related transition of haustorial shape that occurred significantly earlier and at higher frequency in the CSG mutants. These findings point to a function of the homologs of common symbiosis genes in haustorial maintenance thus revealing an overlapping gene set for the intracellular accommodation of hyphal symbionts and pathogens.

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Phys.org: Research shows first land plants were parasitised by microbes (2018)

Phys.org: Research shows first land plants were parasitised by microbes (2018) | Plants and Microbes | Scoop.it

Relationship between plants and filamentous microbes not only dates back millions of years, but modern plants have maintained this ancient mechanism to accommodate and respond to microbial invaders.

 

Why do some plants welcome some microbes with open arms while giving others the cold-shoulder? Like most relationships, it's complicated, and it all goes back a long way. By studying liverworts – which diverged from other land plants early in the history of plant evolution – researchers from the Sainsbury Laboratory at the University of Cambridge have found that the relationship between plants and filamentous microbes not only dates back millions of years, but that modern plants have maintained this ancient mechanism to accommodate and respond to microbial invaders.

 

Published today in the journal Proceedings of the National Academy of Sciences, a new study shows that aggressive filamentous microbial (fungi-like) pathogens can invade liverworts and that some elements of the liverwort's response are shared with distantly related plants. The first author of the paper, Dr. Philip Carella, said the research showed that liverworts could be infected by the common and devastating microorganism Phytophthora: "We know a great deal about microbial infections of modern flowering plants, but until now we haven't known how distantly related plant lineages dealt with an invasion by an aggressive microbe. To test this, we first wanted to see if Phytophthora could infect and complete its life cycle in a liverwort."

 

"We found that Phytophthora palmivora can colonise the photosynthetic tissues of the liverwort Marchantia polymorpha by invading living cells. Marchantia responds to this by deploying proteins around the invading Phytophthora hyphal structures. These proteins are similar to those that are produced in flowering plants such as tobacco, legumes or Arabidopsis in response to infections by both symbiont and pathogenic microbes."

 

These lineages share a common ancestor that lived over 400 million years ago, and fossils from this time period show evidence that plants were already forming beneficial relationships with filamentous microbes. Dr. Carella added: "These findings raise interesting questions about how plants and microbes have interacted and evolved pathogenic and symbiotic relationships. Which mechanisms evolved early in a common ancestor before the plant groups diverged and which evolved independently?"

 

Philip Carella et al. Phytophthora palmivora establishes tissue-specific intracellular infection structures in the earliest divergent land plant lineage, Proceedings of the National Academy of Sciences (2018). DOI: 10.1073/pnas.1717900115

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Bridget Barker's curator insight, April 11, 1:55 PM
I was literally talking about this in my class yesterday. This is solid.
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Current Opinion Plant Biology: Leaf nodule symbiosis: function and transmission of obligate bacterial endophytes (2018)

Current Opinion Plant Biology: Leaf nodule symbiosis: function and transmission of obligate bacterial endophytes (2018) | Plants and Microbes | Scoop.it

Various plant species establish intimate symbioses with bacteria within their aerial organs. The bacteria are contained within nodules or glands often present in distinctive patterns on the leaves, and have been used as taxonomic marker since the early 20th century. These structures are present in very diverse taxa, including dicots (Rubiaceae and Primulaceae) and monocots (Dioscorea). The symbionts colonize the plants throughout their life cycles and contribute bioactive secondary metabolites to the association. In this review, we present recent progress in the understanding of these plant–bacteria symbioses, including the modes of transmission, distribution and roles of the symbionts.


Via Jean-Michel Ané
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Cell Host & Microbe: The Monocot-Specific Receptor-like Kinase SDS2 Controls Cell Death and Immunity in Rice (2018)

• The RLK SDS2 positively regulates plant cell death and immunity in rice
• SDS2 phosphorylates E3 ligase SPL11, which in turn ubiquitinates SDS2 for degradation
• SDS2 phosphorylates receptor-like cytoplasmic kinases RLCK118
• RLCK118 interacts with and phosphorylates the NADPH oxidase OsRbohB

Programmed cell death (PCD) plays critical roles in plant immunity but must be regulated to prevent excessive damage. The E3 ubiquitin ligase SPL11 negatively regulates PCD and immunity in plants. We show that SPL11 cell-death suppressor 2 (SDS2), an S-domain receptor-like kinase, positively regulates PCD and immunity in rice by engaging and regulating SPL11 and related kinases controlling defense responses. An sds2mutant shows reduced immune responses and enhanced susceptibility to the blast fungus Magnaporthe oryzae. Conversely, SDS2 over-expression induces constitutive PCD accompanied by elevated immune responses and enhanced resistance to M. oryzae. SDS2 interacts with and phosphorylates SPL11, which in turn ubiquitinates SDS2, leading to its degradation. In addition, SDS2 interacts with related receptor-like cytoplasmic kinases, OsRLCK118/176, that positively regulate immunity by phosphorylating the NADPH oxidase OsRbohB to stimulate ROS production. Thus, a plasma membrane-resident protein complex consisting of SDS2, SPL11, and OsRLCK118/176 controls PCD and immunity in rice.

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