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Protein Data Bank: 6J5T - Reconstitution and structure of a plant NLR resistosome conferring immunity (2019)

Protein Data Bank: 6J5T - Reconstitution and structure of a plant NLR resistosome conferring immunity (2019) | Plants and Microbes | Scoop.it

This is stunning! Plants have inflammasomes! Structure of the Arabidopsis NLR immune receptor ZAR1 in complex with its guarded kinases RKS1 and PBL2. Paper appears to be in press.

 

Wang, J.Z., Hu, M.J., Wang, J., Qi, J.F., Han, Z.F., Wang, G.X., Qi, Y.J., Wang, H.W., Zhou, J.M., Chai, J.J. 2019. Reconstitution and structure of a plant NLR resistosome conferring immunity. Science --: --

 

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Annual Rev Phytopathol: Flax Rust Resistance Gene Specificity is Based on Direct Resistance-Avirulence Protein Interactions (2007)

Annual Rev Phytopathol: Flax Rust Resistance Gene Specificity is Based on Direct Resistance-Avirulence Protein Interactions (2007) | Plants and Microbes | Scoop.it

Genetic studies of the flax-flax rust interaction led to the formulation of the gene-for-gene hypothesis and identified resistance genes (R) in the host plant and pathogenicity genes, including avirulence (Avr) and inhibitor of avirulence genes (I), in the rust pathogen. R genes have now been cloned from four of the five loci in flax and all encode proteins of the Toll, Interleukin-1 receptor, R gene-nucleotide binding site-leucine-rich repeat (TIR-NBS-LRR) class. Avr genes have been cloned from four loci in flax rust and encode small secreted proteins with no between locus similarity and no close homologs in current data bases. It is postulated that Avr proteins enter the host cell, have virulence effector functions, and in resistant host genotypes, are recognized by direct and specific interaction with host R proteins, leading to activation of rust resistance defense responses. Direct interaction between R and Avr proteins is the basis of gene-for-gene specificity in the flax-flax rust system and both R and Avr genes have the signatures of diversifying selection, suggesting the existence of a coevolutionary arms race between the host plant and its obligate rust pathogen.

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The Plant Pathology Journal: The Current Situation and Future Impacts (2019)

The Plant Pathology Journal: The Current Situation and Future Impacts (2019) | Plants and Microbes | Scoop.it

Wheat blast occurred in Bangladesh for the first time in Asia in 2016. It is caused by a fungal pathogen, Magnaporthe oryzae Triticum (MoT) pathotype. In this review, we focused on the current status of the wheat blast in regard to host, pathogen, and environment. Despite the many efforts to control the disease, it expanded to neighboring regions including India, the world's second largest wheat producer. However, the disease occurrence has definitely decreased in quantity, because of many farmers chose to grow alternate crops according to the government’s directions. Bangladesh government planned to introduce blast resistant cultivars but knowledges about genetics of resistance is limited. The genome analyses of the pathogen population revealed that the isolates caused wheat blast in Bangladesh are genetically close to a South American lineage of Magnaporthe oryzae. Understanding the genomes of virulent strains would be important to find target resistance genes for wheat breeding. Although the drier winter weather in Bangladesh was not favorable for development of wheat blast before, recent global warming and climate change are posing an increasing risk of disease development. Bangladesh outbreak in 2016 was likely to be facilitated by an extraordinary warm and humid weather in the affected districts before the harvest season. Coordinated international collaboration and steady financial supports are needed to mitigate the fearsome wheat blast in South Asia before it becomes a catastrophe.

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Zenodo: NLR singletons, pairs and networks: evolution, assembly and regulation of the intracellular immunoreceptor circuitry of plants (2019)

Zenodo: 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 that trigger a potent broad-spectrum immune reaction known as the hypersensitive response. An emerging paradigm is that plant NLRs form immune signalling 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.

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Nature Biotech: Resistance gene cloning from a wild crop relative by sequence capture and association genetics (2019)

Nature Biotech: Resistance gene cloning from a wild crop relative by sequence capture and association genetics (2019) | Plants and Microbes | Scoop.it

Disease resistance (R) genes from wild relatives could be used to engineer broad-spectrum resistance in domesticated crops. We combined association genetics with R gene enrichment sequencing (AgRenSeq) to exploit pan-genome variation in wild diploid wheat and rapidly clone four stem rust resistance genes. AgRenSeq enables R gene cloning in any crop that has a diverse germplasm panel.


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Nature Ecology & Evolution: The global burden of pathogens and pests on major food crops (2019)

Nature Ecology & Evolution: The global burden of pathogens and pests on major food crops (2019) | Plants and Microbes | Scoop.it

Crop pathogens and pests reduce the yield and quality of agricultural production. They cause substantial economic losses and reduce food security at household, national and global levels. Quantitative, standardized information on crop losses is difficult to compile and compare across crops, agroecosystems and regions. Here, we report on an expert-based assessment of crop health, and provide numerical estimates of yield losses on an individual pathogen and pest basis for five major crops globally and in food security hotspots. Our results document losses associated with 137 pathogens and pests associated with wheat, rice, maize, potato and soybean worldwide. Our yield loss (range) estimates at a global level and per hotspot for wheat (21.5% (10.1–28.1%)), rice (30.0% (24.6–40.9%)), maize (22.5% (19.5–41.1%)), potato (17.2% (8.1–21.0%)) and soybean (21.4% (11.0–32.4%)) suggest that the highest losses are associated with food-deficit regions with fast-growing populations, and frequently with emerging or re-emerging pests and diseases. Our assessment highlights differences in impacts among crop pathogens and pests and among food security hotspots. This analysis contributes critical information to prioritize crop health management to improve the sustainability of agroecosystems in delivering services to societies.

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Molecular Plant Pathology: Pyricularia graminis‐tritici is not the correct species name for the wheat blast fungus: response to Ceresini et al. (2019)

Molecular Plant Pathology: Pyricularia graminis‐tritici is not the correct species name for the wheat blast fungus: response to Ceresini et al. (2019) | Plants and Microbes | Scoop.it

In a review article published in this issue of Molecular Plant Pathology, Ceresini et al. (2019) wrongly treat the wheat blast fungus as a new species, Pyricularia graminis‐tritici (Pygt), following the proposal of Castroagudin et al. (2016). Despite the host specificity implied by the name Pygt, the proposed species concept includes isolates that cause major disease epidemics on finger millet and turf grasses (Castroagudin et al., 2016, 2017). These authors also conclude, based on little evidence, that ‘the hypothesis of grass‐specific populations for the overall Pyricularia oryzae species complex is falsified’. In addition, they stress that the rice blast fungus, which they describe as P. oryzae, ‘may not provide a suitable model for understanding the biology of Pygt’. All of these conclusions are misinformed and have serious consequences. International quarantine regulations are needed to block the movement of this fearsome seed‐borne blast fungus through the trade of seed or grain. The Pygt designation magnifies the challenge by grouping the dangerous, highly aggressive wheat pathogens from South America and Bangladesh, which are readily distinguishable from other P. oryzae lineages, with non‐wheat pathogens that are already found worldwide and are not known to be virulent on wheat or rice. Careful biological analysis of wheat blast host–pathogen interactions has clearly shown that studies of other host‐adapted forms of the fungus are relevant to an understanding of wheat blast and the development of new methods for disease control. Here, we summarize the overwhelming evidence that supports the alternative, internationally recognized designation of Pyricularia oryzae (synonym Magnaporthe oryzae; Zhang et al., 2016) as a single species divided into host‐adapted lineages with limited primary host ranges. We also delineate the errors that led Ceresini et al. (2019) to their false conclusions. The same discussion applies to a second recently published review on the same topic (Ceresini et al., 2018).

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Resource: BRIGIT Vector Borne Disease of Plants (2019)

Resource: BRIGIT Vector Borne Disease of Plants (2019) | Plants and Microbes | Scoop.it

BRIGIT builds a collaborative capability to understand and prevent introduction of arthropod-borne plant pathogens to the UK and the challenges it poses to the UK flora.


Xylella fastidiosa has been described by the European Commission as “one of the most dangerous plant bacteria worldwide”.

 

This insect-transmitted bacterial plant pathogen infects >500 species including crops, ornamental plants, and trees. In Italy alone, over one million olive trees are dying from Xylella in a disease called Olive Quick Decline Syndrome. So far, Xylella has not been reported in the UK.

 

Infected plants can show leaf scorching and loss of leaves or fruit. Although these symptoms may not appear at first, infected plants will eventually die and currently there is no known cure for the disease.

 

Xylella is a bacterial pathogen, transmitted by insects that feed on the xylem, a plant tissue that transports water from roots to leaves in plants. These bugs include sharpshooters in the Americas and spittlebugs/froghoppers in Europe, including the UK. If Xylella-infected plants or carrier insects enter the UK, there is potential for the disease to spread to many plants through native insects or via transport of plants across the UK by humans, with consequences for commercial and amenity horticulture, forestry, crop production, woodlands and wider biodiversity, with economic, environmental and social impacts.

 

Despite this threat, very little is known about how the bacteria might spread in Northern European climates as most research on Xylella and its insect vectors has been based in warmer southern climates. Plants are imported into the UK every day and greater knowledge is required to prevent the further Xylella spread.

 

BRIGIT will develop new methods to detect the bacterium and develop understanding of factors that could contribute to Xylella entry and dispersal in the UK. The project interacts with stakeholders and policymakers to reduce the impacts of Xylella in the UK and mitigate the impacts of the pathogen.

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New Phytologist: Virulence‐ and signaling‐associated genes display a preference for long 3′UTRs during rice infection and metabolic stress in the rice blast fungus (2019)

New Phytologist: Virulence‐ and signaling‐associated genes display a preference for long 3′UTRs during rice infection and metabolic stress in the rice blast fungus (2019) | Plants and Microbes | Scoop.it
  • Generation of mRNA isoforms by alternative polyadenylation (APA) and their involvement in regulation of fungal cellular processes, including virulence, remains elusive. Here, we investigated genome‐wide polyadenylation site (PAS) selection in the rice blast fungus to understand how APA regulates pathogenicity.
  • More than half of Magnaporthe oryzae transcripts undergo APA and show novel motifs in their PAS region. Transcripts with shorter 3′UTRs are more stable and abundant in polysomal fractions, suggesting they are being translated more efficiently. Importantly, rice colonization increases the use of distal PASs of pathogenicity genes, especially those participating in signalling pathways like 14‐3‐3B, whose long 3′UTR is required for infection.
  • Cleavage factor I (CFI) Rbp35 regulates expression and distal PAS selection of virulence and signalling‐associated genes, tRNAs and transposable elements, pointing its potential to drive genomic rearrangements and pathogen evolution. We propose a noncanonical PAS selection mechanism for Rbp35 that recognizes UGUAH, unlike humans, without CFI25.
  • Our results showed that APA controls turnover and translation of transcripts involved in fungal growth and environmental adaptation. Furthermore, these data provide useful information for enhancing genome annotations and for cross‐species comparisons of PASs and PAS usage within the fungal kingdom and the tree of life.
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​Interactions: InterView: Detlef Weigel (2018)

​Interactions: InterView: Detlef Weigel (2018) | Plants and Microbes | Scoop.it

Interactions: What guided your decision to dedicate the next stage of your research career to MPMI? 

Detlef Weigel: My path to MPMI was rather circuitous. Genetics is my first love, and genetic phenomena of any kind appeal to me. Almost 15 years ago, Janne Lempe and Kirsten Bomblies in my lab discovered a syndrome of Arabidopsis hybrid weakness that we at first interpreted as a developmental abnormality. We quickly learned that this syndrome was not specific to Arabidopsis spp. and that it was already well known from many wild and cultivated plants, for which it is called “hybrid necrosis.” Anybody in the MPMI field knows that necrosis is often a hallmark of pathogen infection. Nevertheless, we were apparently the first ones to recognize that inappropriate immune reactions in the absence of pathogens were most likely the defining characteristics of this phenomenon, rather than developmental defects.

 

For us, one of the attractions of studying hybrid necrosis was that we thought it would teach us about speciation, but after many thousands of crosses and having cloned quite a few of the causal genes, we realized that hybrid necrosis has much more to do with how the plant balances the demands on its immune system. With too little immunity, the plant will succumb too quickly to infection, but with too much immunity, the plant will damage itself. Hybrid necrosis occurs when components of the immune system are mismatched, and these components begin to signal even if there is no pathogen trigger. Satisfyingly, the molecular observations in Arabidopsis spp. seemed to match similar observations in several other species. As a matter of fact, with hindsight we realized that the first case of hybrid necrosis that was molecularly understood predated our own work in Arabidopsis—namely, the study of the tomato Cf-2/Rcr3 system by Jonathan Jones.

 

In parallel with our efforts to clone the causal genes for hybrid necrosis in Arabidopsis spp., we could confirm through our whole-genome resequencing and sequencing studies that immune genes—particularly those of the NLR class but also of other smaller families—are the most diverse genes in the Arabidopsis genome. This, in turn, made us wonder what drives this diversity—hence, our current obsession with trying to understand the relationship between Arabidopsis and its natural pathogens in the real world.

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MPMI: Tomato 14-3-3 Proteins Are Required for Xv3 Disease Resistance and Interact with a Subset of Xanthomonas euvesicatoria Effectors (2018)

MPMI: Tomato 14-3-3 Proteins Are Required for Xv3 Disease Resistance and Interact with a Subset of Xanthomonas euvesicatoria Effectors (2018) | Plants and Microbes | Scoop.it

The 14-3-3 phospho-binding proteins with scaffolding activity play central roles in the regulation of enzymes and signaling complexes in eukaryotes. In plants, 14-3-3 isoforms are required for disease resistance and key targets of pathogen effectors. Here, we examined the requirement of the tomato (Solanum lycopersicum) 14-3-3 isoform (TFT) protein family for Xv3 disease resistance in response to the bacterial pathogen Xanthomonas euvesicatoria. In addition, we determined whether TFT proteins interact with the repertoire of X. euvesicatoria type III secretion effector proteins, including AvrXv3, the elicitor of Xv3 resistance. We show that multiple TFT contribute to Xv3resistance. We also show that one or more TFT proteins physically interact with multiple effectors (AvrXv3, XopE1, XopE2, XopN, XopO, XopQ, and XopAU). Genetic analyses indicate that none of the identified effectors interfere with AvrXv3-elicited resistance into Xv3 tomato leaves; however, XopE1, XopE2, and XopO are required to suppress symptom development in susceptible tomato leaves. Phospho-peptide mapping revealed that XopE2 is phosphorylated at multiple residues in planta and residues T66, T131, and S334 are required for maximal binding to TFT10. Together, our data support the hypothesis that multiple TFT proteins are involved in immune signaling during X. euvesicatoria infection.

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bioRxiv: Novel haplotypes and networks of AVR-Pik alleles in Magnaporthe oryzae (2018)

bioRxiv: Novel haplotypes and networks of AVR-Pik alleles in Magnaporthe oryzae (2018) | Plants and Microbes | Scoop.it

Rice blast disease is one of the most destructive fungal diseases of rice world-wide. The avirulence (AVR) genes of Magnaporthe oryzae are recognized by the cognate resistance (R) genes of rice, and trigger race specific resistance. Here, we studied the possible evolutionary pathways in the evolution of AVR-Pik alleles by analyzing the DNA sequence variation and assayed for their avirulence function to the cognate Pik alleles resistance genes under field conditions in China. Results of PCR products showed that 278 isolates of M. oryzae carry AVR-Pik alleles among genomic DNA of 366 isolates of M. oryzae collected from Yunnan Province, China. Among of them, 66.7-90.3% of M. oryzae carry AVR-Pik alleles from six regions of Yunnan. Moreover, 10 AVR-Pik haplotypes encoding five novel AVR-Pik variants were identified among 201 isolates. The AVR-Pik alleles stepwise evolved to virulence from avirulent forms via base substitution. These findings demonstrate that AVR-Pik alleles are under positive selection and mutations are responsible for defeating race-specific resistance Pik alleles in nature.

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bioRxiv: Sulfated RaxX, which represents an unclassified group of ribosomally synthesized post-translationally modified peptides, binds a host immune receptor (2018)

bioRxiv: Sulfated RaxX, which represents an unclassified group of ribosomally synthesized post-translationally modified peptides, binds a host immune receptor (2018) | Plants and Microbes | Scoop.it

The rice immune receptor XA21 is activated by the sulfated microbial peptide RaxX (required for activation of XA21-mediated immunity X) produced by Xanthomonas oryzae pv. oryzae (Xoo). Mutational studies and targeted proteomics revealed that RaxX is processed and secreted by the protease/transporter RaxB, whose function can be partially fulfilled by a noncognate peptidase-containing transporter B (PctB). RaxX 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 founding member of a previously unclassified and understudied group of tyrosine sulfated RiPPs (ribosomally synthesized, post-translationally modified peptides). 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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Zenodo: Open science to tackle a cereal killer on the run (2019)

Zenodo: Open science to tackle a cereal killer on the run (2019) | Plants and Microbes | Scoop.it

Outbreaks of emerging plant diseases and insect pests are increasing at an alarming rate threatening the food security needs of a booming world population. The role of plant pathologists in addressing these threats to plant health is critical. This report elaborates our personal experience with the appearance in Bangladesh of a destructive new fungal disease wheat blast. Here we recap our experience and stress the importance of open science platforms and crowdsourced community responses in tackling emerging plant diseases. Benefits of the open science approach include recruitment of multidisciplinary experts, application of cutting-edge methods and timely replication of data analyses to increase the robustness of the findings.

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Zenodo: Rmg8 confers resistance to the Bangladeshi lineage of the wheat blast fungus (2019)

Zenodo: Rmg8 confers resistance to the Bangladeshi lineage of the wheat blast fungus (2019) | Plants and Microbes | Scoop.it

First reported in South America, wheat blast, caused by the fungus Magnaporthe oryzae(Syn. Pyricularia oryzae), has recently spread to Bangladesh and is threatening neighboring South Asian countries. To date, only a few resistance genes have been identified to function against wheat blast. Whether these genes are effective against the Bangaldeshi lineage of the wheat blast fungus is unknown. Here, we found that a hexaploid common wheat line S-615 carrying the gene Rmg8is resistant to M. oryzaeBangladeshi isolate BTJP4-1 but susceptible to Brazilian isolate N06047. These findings are consistent with the observation that AvrRmg8, which encodes the avirulence effector protein recognized by Rmg8, is present in Bangladeshi isolates of the wheat blast fungus. These results indicate that Rmg8could contribute to breeding blast resistant wheat varieties adapted to South Asian conditions.

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PNAS: Intercellular cooperation in a fungal plant pathogen facilitates host colonization (2019)

PNAS: Intercellular cooperation in a fungal plant pathogen facilitates host colonization (2019) | Plants and Microbes | Scoop.it

Cooperation between specialized cells and organisms supports complex biological functions, from the colonization of unfavorable environments to the formation of organs and sociality. Some bacterial pathogens are known to rely on cooperation between individuals and species for efficient colonization of their host and the onset of disease. We examined the regulation of genes in cells from different parts of a fungal plant pathogen and found evidence for cooperation between these fungal cells. We further show that cooperation between fungal cells is particularly important for the efficient colonization of resistant plants. These findings establish cooperation as a mechanism supporting disease caused by fungal pathogens that should be taken into account in the design of disease management strategies.

Cooperation is associated with major transitions in evolution such as the emergence of multicellularity. It is central to the evolution of many complex traits in nature, including growth and virulence in pathogenic bacteria. Whether cells of multicellular parasites function cooperatively during infection remains, however, largely unknown. Here, we show that hyphal cells of the fungal pathogen Sclerotinia sclerotiorum reprogram toward division of labor to facilitate the colonization of host plants. Using global transcriptome sequencing, we reveal that gene expression patterns diverge markedly in cells at the center and apex of hyphae during Arabidopsis thaliana colonization compared with in vitro growth. We reconstructed a genome-scale metabolic model for S. sclerotiorum and used flux balance analysis to demonstrate metabolic heterogeneity supporting division of labor between hyphal cells. Accordingly, continuity between the central and apical compartments of invasive hyphae was required for optimal growth in planta . Using a multicell model of fungal hyphae, we show that this cooperative functioning enhances fungal growth predominantly during host colonization. Our work identifies cooperation in fungal hyphae as a mechanism emerging at the multicellular level to support host colonization and virulence.


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New Phytologist: Diverse NLR immune receptors activate defence via the RPW8‐NLR NRG1 (2018)

New Phytologist: Diverse NLR immune receptors activate defence via the RPW8‐NLR NRG1 (2018) | Plants and Microbes | Scoop.it

Most land‐plant genomes carry genes that encode RPW8‐NLR resistance (R) proteins. Angiosperms carry two RPW8‐NLR subclasses: ADR1 and NRG1. ADR1s act as ‘helper’ NLRs for multiple TIR‐ and CC‐NLR R proteins in Arabidopsis. In angiosperm families, NRG1 co‐occurs with TIR‐NLR Resistance (R) genes. We tested if NRG1 is required for signalling of multiple TIR‐NLRs.

Using CRISPR mutagenesis, we obtained an nrg1a‐nrg1b double mutant in two Arabidopsis accessions, and an nrg1 mutant in Nicotiana benthamiana.

 

These mutants are compromised in signalling of all TIR‐NLRs tested, including WRR4A, WRR4B, RPP1, RPP2, RPP4 and the pairs RRS1/RPS4, RRS1B/RPS4B, CHS1/SOC3 and CHS3/CSA1. In Arabidopsis, NRG1 is required for the hypersensitive cell‐death response (HR) and full oomycete resistance, but not for salicylic acid induction or bacterial resistance. By contrast, nrg1 loss‐of‐function does not compromise the CC‐NLR R proteins RPS5 and MLA. RPM1 and RPS2 (CC‐NLRs) function is slightly compromised in an nrg1mutant. Thus, NRG1 is required for full TIR‐NLR function and contributes to the signalling of some CC‐NLRs.

 

Some NRG1‐dependent R proteins also signal partially via the NRG1 sister clade, ADR1. We propose that some NLRs signal via NRG1 only, some via ADR1 only and some via both or neither.


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New Phytologist: Commentary: Convergence of cell‐surface and intracellular immune receptor signalling (2019)

New Phytologist: Commentary: Convergence of cell‐surface and intracellular immune receptor signalling (2019) | Plants and Microbes | Scoop.it

This article is a Commentary on Kadota et al., 221: 2160–2175.

 

Plant immune responses are initiated by recognition of pathogen invasion through immune receptors. The pathogen sensing system is mainly composed of two structurally different proteins that are located on different subcellular compartments. One is the plasma membrane‐localized pattern recognition receptors (PRRs) that detect pathogen‐associated molecular patterns (PAMPs) (Boutrot & Zipfel, 2017). PRRs perceive extracellular PAMPs to activate PAMP‐triggered immunity (PTI). In turn, adapted pathogens interfere with or modulate host signalling by virulence factors (called effectors) for successful infection. The other is intracellular nucleotide‐binding domain and leucine‐rich repeat proteins (NLRs) that recognize these effectors (Jones et al., 2016). Activation of an NLR induces a robust immune response called effector‐triggered immunity (ETI), which is often accompanied by hypersensitive response (HR) cell death. Animals encode both plasma membrane and intracellular immune receptors, which share similar structures with plant PRRs and NLRs for recognition of PAMPs; but plant and animal immune receptors evolved independently (Ronald & Beutler, 2010; Jones et al., 2016). Interestingly, although PRRs and NLRs are structurally different and localize in distinct subcellular compartments, they share substantial downstream signalling, such as Ca2+, mitogen‐activated protein kinase (MAPK), reactive oxygen species (ROS), and phytohormone signalling as well as massive transcriptional reprogramming (Peng et al., 2018). However, it is not known how PRRs and NLRs activate similar signalling outputs. In this issue of New Phytologist, Kadota et al. (2019, pp. 2160–2175) investigated protein phosphorylation dynamics upon NLR activation by phosphoproteomics. By comparing with previously published phosphoproteomics data for PTI, they discovered that phosphorylation occurred in the same residues of an NADPH oxidase, RESPIRATORY BURST OXIDASE HOMOLOGUE D (RBOHD), which is activated during both PTI and ETI. Thus, Kadota et al. (2019) precisely defined a signal convergent point between PRR and NLR signalling at the molecular level.


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bioRxiv: The Arabidopsis thaliana pan-NLRome (2019)

bioRxiv: The Arabidopsis thaliana pan-NLRome (2019) | Plants and Microbes | Scoop.it

Disease is both among the most important selection pressures in nature and among the main causes of yield loss in agriculture. In plants, resistance to disease is often conferred by Nucleotide-binding Leucine-rich Repeat (NLR) proteins. These proteins function as intracellular immune receptors that recognize pathogen proteins and their effects on the plant. Consistent with evolutionarily dynamic interactions between plants and pathogens, NLRs are known to be encoded by one of the most variable gene families in plants, but the true extent of intraspecific NLR diversity has been unclear. Here, we define the majority of the Arabidopsis thaliana species-wide 'NLRome'. From NLR sequence enrichment and long-read sequencing of 65 diverse A. thaliana accessions, we infer that the pan-NLRome saturates with approximately 40 accessions. Despite the high diversity of NLRs, half of the pan-NLRome is present in most accessions. We chart the architectural diversity of NLR proteins, identify novel architectures, and quantify the selective forces that act on specific NLRs, domains, and positions. Our study provides a blueprint for defining the pan-NLRome of plant species.

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bioRxiv: Cross-reactivity of a rice NLR immune receptor to distinct effectors from the blast pathogen leads to partial disease resistance (2019)

bioRxiv: Cross-reactivity of a rice NLR immune receptor to distinct effectors from the blast pathogen leads to partial disease resistance (2019) | Plants and Microbes | Scoop.it

Unconventional integrated domains in plant intracellular immune receptors (NLRs) can directly bind translocated pathogen effector proteins to initiate an immune response. The rice immune receptor pairs Pik-1/Pik-2 and RGA5/RGA4 both use integrated heavy metal-associated (HMA) domains to bind the Magnaporthe oryzae effectors AVR-Pik and AVR-Pia, respectively. These effectors both belong to the MAX effector family and share a core structural fold, despite being divergent in sequence. How integrated domains maintain specificity of recognition, even for structurally similar effectors, has implications for understanding plant immune receptor evolution and function. Here we show that the rice NLR pair Pikp-1/Pikp-2 triggers an immune response leading to partial disease resistance towards the mis-matched effector AVR-Pia in planta, and that the Pikp-HMA domain binds AVR-Pia in vitro. The HMA domain from another Pik-1 allele, Pikm, is unable to bind AVR-Pia, and does not trigger a response in plants. The crystal structure of Pikp-HMA bound to AVR-Pia reveals a different binding interface compared to AVR-Pik effectors, suggesting plasticity in integrated domain/effector interactions. This work shows how a single NLR can bait multiple pathogen effectors via an integrated domain, and may enable engineering immune receptors with extended disease resistance profiles.

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Phytopathology: Microsatellite Analysis and Urediniospore Dispersal Simulations Support the Movement of Puccinia graminis f. sp. tritici from Southern Africa to Australia (2019)

Phytopathology: Microsatellite Analysis and Urediniospore Dispersal Simulations Support the Movement of Puccinia graminis f. sp. tritici from Southern Africa to Australia (2019) | Plants and Microbes | Scoop.it

The Australian wheat stem rust (Puccinia graminis f. sp. tritici) population was shaped by the introduction of four exotic incursions into the country. It was previously hypothesized that at least two of these (races 326-1,2,3,5,6 and 194-1,2,3,5,6 first detected in 1969) had an African origin and moved across the Indian Ocean to Australia on high-altitude winds. We provide strong supportive evidence for this hypothesis by combining genetic analyses and complex atmospheric dispersion modeling. Genetic analysis of 29 Australian and South African P. graminis f. sp. tritici races using microsatellite markers confirmed the close genetic relationship between the South African and Australian populations, thereby confirming previously described phenotypic similarities. Lagrangian particle dispersion model simulations using finely resolved meteorological data showed that long distance dispersal events between southern Africa and Australia are indeed possible, albeit rare. Simulated urediniospore transmission events were most frequent from central South Africa (viable spore transmission on approximately 7% of all simulated release days) compared with other potential source regions in southern Africa. The study acts as a warning of possible future P. graminis f. sp. tritici dispersal events from southern Africa to Australia, which could include members of the Ug99 race group, emphasizing the need for continued surveillance on both continents.

 

Check the videos of simulated atmospheric long-distance dispersal and deposition of Puccinia graminis f. sp. tritici urediniospores from Africa.

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New Phytologist: Dude, where is my mutant? Nicotiana benthamiana meets forward genetics (2019)

New Phytologist: Dude, where is my mutant? Nicotiana benthamiana meets forward genetics (2019) | Plants and Microbes | Scoop.it

Nicotiana benthamiana, a solanaceous species native to Australia, is one of the most commonly used model plant organisms. It was initially used by the virology community because of its hyper‐susceptibility to plant viruses. Later, this feature was exploited with the development of viral vectors that can express foreign genes and the establishment of virus‐induced gene silencing (VIGS), which enabled knocking down endogenous plant genes. Benth (or Benthi), as it is colloquially known, was further popularized by the development of agroinfiltration, a method that enabled transient protein expression in plants. Agroinfiltration has been extensively used in cell biology, biochemistry, protein–protein interaction analyses and other in planta studies (Goodin et al., 2008). However, genetic analyses of N. benthamiana remained limited due to its allotetraploid nature and incomplete sequence of the 3.1 Gb genome. In this issue of New Phytologist, Schultink et al. (pp. 1001–1009) used a forward genetic screen in N. benthamiana to determine that NbZAR1, an orthologue of the Arabidopsis thaliana NLR (nucleotide‐binding domain and leucine‐rich repeat domain‐containing) ZAR1, is responsible for the perception of XopJ4 from the tomato bacterial pathogen Xanthomonas perforans. Although forward genetic screens using gene silencing have been performed in N. benthamiana, Schultink et al. are among the first to use a chemical mutagenesis‐based screen to dissect plant biological processes. Together with CRISPR genome editing and improved genomics resources, this study ushers in a new era of forward and reverse genetic analyses for this much‐cherished model plant system (Fig. 1).

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Scientific Reports: Stable pH Suppresses Defense Signaling and is the Key to Enhance Agrobacterium -Mediated Transient Expression in Arabidopsis Seedlings (2018)

Scientific Reports: Stable pH Suppresses Defense Signaling and is the Key to Enhance Agrobacterium -Mediated Transient Expression in Arabidopsis Seedlings (2018) | Plants and Microbes | Scoop.it

Agrobacterium-mediated transient expression is a powerful analysis platform for diverse plant gene functional studies, but the mechanisms regulating the expression or transformation levels are poorly studied. Previously, we developed a highly efficient and robust Agrobacterium-mediated transient expression system, named AGROBEST, for Arabidopsis seedlings. In this study, we found that AGROBEST could promote the growth of agrobacteria as well as inhibit the host immunity response. When the factor of agrobacterial growth is minimized, maintaining pH at 5.5 with MES buffer was the key to achieving optimal transient expression efficiency. The expression of plant immunity marker genes, FRK1 and NHL10, was suppressed in the pH-buffered medium as compared with non-buffered conditions in Col-0 and an efr-1 mutant lacking the immunity receptor EFR recognizing EF-Tu, a potent pathogen- or microbe-associated molecular pattern (PAMP or MAMP) of A. tumefaciens. Notably, such immune suppression could also occur in Arabidopsis seedlings without Agrobacterium infection. Furthermore, the PAMP-triggered influx of calcium ions was compromised in the pH-buffered medium. We propose that the enhanced transient expression efficiency by stable pH was due to inhibiting calcium ion uptake and subsequently led to suppressing immunity against Agrobacterium.

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Conference: Molecular Biology of Plant Pathogens 2019 - 18-19 March 2019, John Innes Centre

Conference: Molecular Biology of Plant Pathogens 2019 - 18-19 March 2019, John Innes Centre | Plants and Microbes | Scoop.it
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NPR: Scientists Are Fighting For The Stricken Pickle Against This Tricky Disease (2018)

NPR: Scientists Are Fighting For The Stricken Pickle Against This Tricky Disease (2018) | Plants and Microbes | Scoop.it

Downy mildew, once just a nuisance, has evolved into a devastating adversary to the pickle, as it now quickly adapts to fungicides and pickle hybrids, and can lay waste to crops in a matter of days.

 

The pickle is in peril. Each summer since the mid 2000s, Florida winds carry downy mildew to cucumber fields north. By summer's end, the disease reaches Michigan, leaving a trail of withered leaves and thwarted pickling plans.

 

With failed harvests, fewer growers are taking a chance on cucumbers. According to USDA records, pickling cucumber acreage declined nearly 25 percent between 2004 and 2015. Globally, downy mildew threatens fields as far flung as India, Israel, Mexico and China.

 

"This is the number one threat to the pickle industry," says vegetable pathologist Lina Quesada-Ocampo of North Carolina State University. The growers, she says, lose money on failed crops and pricey fungicides. "It is a really bad double whammy."

 

Fortunately for pickle lovers, vegetable breeder Michael Mazourek of Cornell University is close to releasing varieties that resist downy mildew. "It's been one of our proudest David and Goliath stories," he says. But his success hinges on funding at a time when public support of agricultural research is declining.

 

The story of saving the pickle, then, is not just about preserving the deli sandwich's sidekick. It's a story of how much we value our food supply. And who we think should pay to protect it.

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