Host-pathogen interaction
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Agriculture | Free Full-Text | Taro Leaf Blight—A Threat to Food Security

Abstract: Taro leaf blight (caused by the Oomycete Phytophthora colocasiae) is a disease of major importance in many regions of the world where taro is grown. Serious outbreaks of taro leaf blight in Samoa in 1993 and in the last few years in Cameroon, Ghana and Nigeria continue to demonstrate the devastating impact of this disease on the livelihoods and food security of small farmers and rural communities dependent on the crop. The spread of the disease to new geographical areas also poses a major threat to neighbouring countries and taro growing regions still free from the disease. Past research, particularly in the Pacific, has demonstrated that management measures such as chemical and cultural control are largely ineffective and that breeding for disease resistance is the most sustainable approach to manage the disease. Recently, the Pacific and South-east Asian regional taro networks have made excellent progress in developing cultivars resistant to taro leaf blight through enhanced utilization of taro genetic resources and close collaboration between farmers and researchers in breeding programs. These programs have secured vital taro genetic resources for future use. This paper provides an overview of the disease, its origin, distribution, biology, epidemiology, management and global impact. The paper will largely focus on breeding strategies to address the disease including challenges, opportunities and constraints. It also discusses how these breeding experiences and outputs can be scaled up to other geographical areas where the disease has been recently introduced or under threat of introduction.


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A novel elicitor protein from Phytophthora parasitica induces plant basal immunity and systemic acquired resistance - Chang - 2014 - Molecular Plant Pathology - Wiley Online Library

A novel elicitor protein from Phytophthora parasitica induces plant basal immunity and systemic acquired resistance - Chang - 2014 - Molecular Plant Pathology - Wiley Online Library | Host-pathogen interaction | Scoop.it

The interaction between Phytophthora pathogens and host plants involves the exchange of complex molecular signals from both sides. Recent studies of Phytophthora have led to the identification of various apoplastic elicitors known to trigger plant immunity. Here, we provide evidence that the protein encoded by OPEL of Phytophthora parasitica is a novel elicitor. Homologues of OPEL were identified only in oomycetes, but not in fungi and other organisms. Quantitative reverse transcription-polymerase chain reaction (RT-PCR) revealed that OPEL is expressed throughout the development of P. parasitica and is especially highly induced after plant infection. Infiltration of OPEL recombinant protein from Escherichia coli into leaves of Nicotiana tabacum (cv. Samsun NN) resulted in cell death, callose deposition, the production of reactive oxygen species and induced expression of pathogen-associated molecular pattern (PAMP)-triggered immunity markers and salicylic acid-responsive defence genes. Moreover, the infiltration conferred systemic resistance against a broad spectrum of pathogens, including Tobacco mosaic virus, the bacteria wilt pathogen Ralstonia solanacearum and P. parasitica. In addition to the signal peptide, OPEL contains three conserved domains: a thaumatin-like domain, a glycine-rich protein domain and a glycosyl hydrolase (GH) domain. Intriguingly, mutation of a putative laminarinase active site motif in the predicted GH domain abolished its elicitor activity, which suggests enzymatic activity of OPEL in triggering the defence response.


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Environmental Microbiology (2014): The heat shock transcription factor PsHSF1 of Phytophthora sojae is required for oxidative stress tolerance and detoxifying the plant oxidative burst

Environmental Microbiology (2014): The heat shock transcription factor PsHSF1 of Phytophthora sojae is required for oxidative stress tolerance and detoxifying the plant oxidative burst | Host-pathogen interaction | Scoop.it

In the interaction between plant and microbial pathogens, reactive oxygen species (ROS) rapidly accumulate upon pathogen recognition at the infection site and play a central role in plant defense. However, the mechanisms that plant pathogens use to counteract ROS are still poorly understood especially in oomycetes, filamentous organisms that evolved independently from fungi. ROS detoxification depends on transcription factors (TFs) that are highly conserved in fungi but much less conserved in oomycetes. In this study we indentified the transcription factor PsHSF1 that acts as a modulator of the oxidative stress response in the soybean stem and root rot pathogen Phytophthora sojae. We found that PsHSF1 is critical for pathogenicity in P. sojae by detoxifying the plant oxidative burst. ROS produced in plant defense can be detoxified by extracellular peroxidases and laccases which might be regulated by PsHSF1. Our study extends the understanding of ROS detoxification mechanism mediated by a heat shock TF in oomycetes.


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Why Sequence Phytophthora capsici? - DOE Joint Genome Institute

Phytophthora capsici is a devastating pathogen of vegetable crops such as cucurbits (squashes, pumpkins, etc.), tomatoes, and peppers. A pathogen of national economic importance, it has recently expanded its host range to include legumes.
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Acquired Resistance to Mefenoxam in Sensitive I...

Acquired Resistance to Mefenoxam in Sensitive I... | Host-pathogen interaction | Scoop.it
The systemic fungicide mefenoxam has been important in the control of late blight disease caused by Phytophthora infestans.
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Identification of Three Elicitins and a Galactan-Based Complex Polysaccharide from a Concentrated Culture Filtrate of Phytophthora infestans Efficient against Pectobacterium atrosepticum.

Identification of Three Elicitins and a Galactan-Based Complex Polysaccharide from a Concentrated Culture Filtrate of Phytophthora infestans Efficient against Pectobacterium atrosepticum. | Host-pathogen interaction | Scoop.it

The induction of plant immunity by Pathogen Associated Molecular Patterns (PAMPs) constitutes a powerful strategy for crop protection. PAMPs indeed induce general defense responses in plants and thus increase plant resistance to pathogens. Phytophthora infestans culture filtrates (CCFs) are known to induce defense responses and decrease the severity of soft rot due to Pectobacterium atrosepticum in potato tubers. The aim of this study was to identify and characterize the active compounds from P. infestans filtrate. The filtrate was fractionated by gel filtration, and the protection effects against P. atrosepticum and the ability to induce PAL activity were tested for each fraction. The fraction active in protection (F1) also induced PAL activity, as did the whole filtrate. Three elicitins (INF1, INF4 and INF5) were identified in F1b, subfraction of F1, by MALDI-TOF-MS and MS/MS analyses. However, deproteinized F1b still showed biological activity against the bacterium, revealing the presence of an additional active compound. GC-MS analyses of the deproteinized fraction highlighted the presence of a galactan-based complex polysaccharide. These experiments demonstrate that the biological activity of the CCF against P. atrosepticum results from a combined action of three elicitins and a complex polysaccharide, probably through the activation of general defense responses.


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Strategies of attack and defence in woody plant–Phytophthora interactions

Strategies of attack and defence in woody plant–Phytophthora interactions | Host-pathogen interaction | Scoop.it

This review comprises both well-known and recently described Phytophthora species and concentrates on Phytophthora–woody plant interactions. First, comprehensive data on infection strategies are presented which were the basis for three models that explain invasion and spread of Phytophthora pathogens in different woody host plants. The first model describes infection of roots, the second concentrates on invasion of the trunk, and the last one summarizes infection and invasion of host plants via leaves. On the basis of morphological, physiological, biochemical and molecular data, scenarios are suggested which explain the sequences of reactions that occur in susceptible and tolerant plants following infections of roots or of stem bark. Particular emphasis is paid to the significance ofPhytophthora elicitins for such host–pathogen interactions. The overall goal is to shed light on the sequences of pathogenesis to better understand how Phytophthora pathogens harm their host plants.


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Filamentous pathogen effector functions: of pathogens, hosts and microbiomes

Filamentous pathogen effector functions: of pathogens, hosts and microbiomes | Host-pathogen interaction | Scoop.it

Microorganisms play essential roles in almost every environment on earth. For instance, microbes decompose organic material, or establish symbiotic relationships that range from pathogenic to mutualistic. Symbiotic relationships have been particularly well studied for microbial plant pathogens and have emphasized the role of effectors; secreted molecules that support host colonization. Most effectors characterized thus far play roles in deregulation of host immunity. Arguably, however, pathogens not only deal with immune responses during host colonization, but also encounter other microbes including competitors, (myco)parasites and even potential co-operators. Thus, part of the effector catalog may target microbiome co-inhabitants rather than host physiology.


Via Niklaus Grunwald, Alejandro Rojas
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PlantVillage: Keeping Up With The Plant Destroyers (2014)

PlantVillage: Keeping Up With The Plant Destroyers (2014) | Host-pathogen interaction | Scoop.it

Readers of PlantVillage who visited popular pages like the one on tomato late blight would have come across the term “oomycetes” and probably wondered what in the world is an oomycete? It’s the taxon of microbes that groups many plant pathogens such as Phytophthora, Pythium, and the downy mildews. These are destructive pathogens of plants. Phytophthora, which stems from Greek words meaning plant-destroyer, is a diverse group of plant pathogens with over 100 species known to science . It includes the infamous Irish potato famine pathogen Phytophthora infestans. When this pathogen reached Ireland in the 1840s, it triggered famine and mayhem with one million people dead and another million forced to leave the island. Today, the late blight disease caused by P. infestans threatens not only tomatoes and potatoes in your gardens but also commercial and subsistence farming worldwide. Matt Fisher, Sarah Gurr and their colleagues recently estimated that losses due to late blight add up to enough calories to feed hundreds of millions of people.

 

So what are these oomycetes that are so feared by gardeners and farmers alike? Traditionally oomycetes were thought to be fungi (yeasts, molds and mushrooms). They are not. Modern methods of evolutionary analyses, known as phylogenetics, have cemented the view that oomycetes are only distant relatives of the fungi. In fact, fungi are more closely related to you and I than they are to the oomycetes. Oomycete biologists like to quip “bats are not birds, dolphins are not fish, and oomycetes are not fungi.” In fact, oomycetes turned out to have unexpected marine cousins in brown algae (kelp) and diatoms in a grouping known as the heterokonts. Oomycetes form a very deep branch in the tree of life and may have evolved from marine parasitic microorganisms. Just a few months ago, while I was visiting Christine Strullu-Derrien and Paul Kenrick at the Natural History Museum in London, I had the amazing opportunity to hold a fossil oomycete that is 300 million year old. Already in those ancient times, oomycetes were successful colonizers of plants and may even have been parasitic.

 

But evolution is a complicated process. More often than widely assumed, it proceeded as a reticulate network rather than a straight line. One example is the transfer of genes from one organism to another. This process, known as horizontal or lateral gene transfer, has occurred frequently in bacteria but is not as well documented in more complex organisms like oomycetes and fungi. Nonetheless, Tom Richard and colleagues at Exeter University reported that oomycetes have at some point in their evolution acquired genes from fungi. Whether this took place hundreds million years ago or more recently is not yet resolved. But as Tom likes to say “oomycetes are 99% not fungi”. How this phenomenon has contributed to the evolution of oomycetes into destructive plant pathogens is an interesting research topic.

 

But why all the misery? Why are oomycetes the scourge of farmers worldwide? The truth is, although Phytophthora are astonishing plant killers that can wipe out crops in days, the secret of their success is their ability to rapidly adapt to resistant plant varieties. Just like the constantly morphing flu virus, the potato blight pathogen and its relatives continuously spawn new races adapted to the resistant varieties released by plant breeders and even occasionally to new host plants. Like Lewis Carroll’s fictional Red Queen, plant breeders and biotechnologists only hope is to strenuously run to keep in the same place. If only we could produce resistant varieties more often then perhaps we’ll have a chance to outrace the ever-evolving blight pathogen.

 

So while you lament your blighted potatoes and your dying tomatoes, take a moment to ponder over the awesome parasite that’s making your vegetable garden look so gloomy. That microbe has already colonized plants way before humans emerged on earth. And for hundreds of millions of years it has kept on changing, evolving, and adapting ensuring its uninterrupted survival on an astonishing array of plant species and varieties. When humans domesticated plants, it could not resist the offering and adopted the crops as its new hosts. Ultimately, it moved to new continents and farmlands causing misery and despair. But we haven’t given up. Plant pathologists are hard at work learning more about these parasites and applying new knowledge and technologies to build disease-resistant crops.


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

Plant Cell: Phytophthora infestans RXLR Effector PexRD2 Interacts with Host MAPKKKε to Suppress Plant Immune Signaling (2014) | Host-pathogen interaction | Scoop.it

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


Via Suayib Üstün, Kamoun Lab @ TSL
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Suayib Üstün's curator insight, March 14, 2014 3:52 PM

What a great week for effector biology!!

Freddy Monteiro's comment, March 14, 2014 8:42 PM
Indeed! A crazy week. You guys belong to an excellent generation of scientists.
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The Potential for Spread of Phytophthora Blight of Cucurbits and ...

The Potential for Spread of Phytophthora Blight of Cucurbits and ... | Host-pathogen interaction | Scoop.it
Excerpts taken from ONvegetables in the Grower, April 2014. A full pdf version of this article is available at 2014_Infosheet_Phytophthora-in-irrigation-water Phytophthora blight (Phytophthora capsici) is a serious and ...
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Phytophthora - Stop the spread - YouTube

A group of over 20 organisations from the public sector, charities and the private sector have got together to produce two videos to help tackle the threat p... (Just watching "Phytophthora...(the plant destroyer)": the movie!
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Roles of small RNAs in soybean defense against Phytophthora sojae infection

Roles of small RNAs in soybean defense against Phytophthora sojae infection | Host-pathogen interaction | Scoop.it

The genus Phytophthora consists of many notorious pathogens of crops and forestry trees. At present, battling Phytophthora diseases is challenging due to a lack of understanding of their pathogenesis. We investigated the role of small RNAs in regulating soybean defense in response to infection by Phytophthora sojae, the second most destructive pathogen of soybean. Small RNAs, including microRNAs (miRNAs) and small interfering RNAs (siRNAs), are universal regulators that repress target gene expression in eukaryotes. We identified known and novel small RNAs that differentially accumulated during P. sojae infection in soybean roots. Among them, miR393 and miR166 were induced by heat-inactivated P. sojae hyphae, indicating that they may be involved in soybean basal defense. Indeed, knocking down the level of mature miR393 led to enhanced susceptibility of soybean to P. sojae; furthermore, the expression of isoflavonoid biosynthetic genes was drastically reduced in miR393 knockdown roots. These data suggest that miR393 promotes soybean defense against P. sojae. In addition to miRNAs, P. sojae infection also resulted in increased accumulation of phased siRNAs (phasiRNAs) that are predominantly generated from canonical resistance genes encoding nucleotide binding-leucine rich repeat proteins and genes encoding pentatricopeptide repeat-containing proteins. This work identifies specific miRNAs and phasiRNAs that regulate defense-associated genes in soybean during Phytophthora infection.


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Molecular Plant Pathology: The Top 10 oomycete pathogens in molecular plant pathology (2014)

Molecular Plant Pathology: The Top 10 oomycete pathogens in molecular plant pathology (2014) | Host-pathogen interaction | Scoop.it

Oomycetes form a deep lineage of eukaryotic organisms that includes a large number of plant pathogens that threaten natural and managed ecosystems. We undertook a survey to query the community for their ranking of plant pathogenic oomycete species based on scientific and economic importance. In total, we received 263 votes from 62 scientists in 15 countries for a total of 33 species. The Top 10 species and their ranking are: (1) Phytophthora infestans; (2, tied) Hyaloperonospora arabidopsidis; (2, tied) Phytophthora ramorum; (4) Phytophthora sojae; (5) Phytophthora capsici; (6) Plasmopara viticola; (7) Phytophthora cinnamomi; (8, tied) Phytophthora parasitica; (8, tied) Pythium ultimum; and (10) Albugo candida. The article provides an introduction to these 10 taxa and a snapshot of current research. We hope that the list will serve as a benchmark for future trends in oomycete research.


See also [link below]:

 

Top 10 plant-parasitic nematodes in molecular plant pathology
Top 10 plant viruses in molecular plant pathology
Top 10 plant pathogenic bacteria in molecular plant pathology
The Top 10 fungal pathogens in molecular plant pathology

 

http://onlinelibrary.wiley.com/journal/10.1111/(ISSN)1364-3703/homepage/free_poster.htm


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Sophien Kamoun on Twitter: "#NPW10 Seb Schornack @dromius: Phytophthora palmivora is a cosmopolite omnivore that likes it hot! http://t.co/b9dcu1mw03"

Sophien Kamoun on Twitter: "#NPW10 Seb Schornack @dromius: Phytophthora palmivora is a cosmopolite omnivore that likes it hot! http://t.co/b9dcu1mw03" | Host-pathogen interaction | Scoop.it
RT @KamounLab: #NPW10 Seb Schornack @dromius: Phytophthora palmivora is a cosmopolite omnivore that likes it hot! http://t.co/b9dcu1mw03
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Phosphite-induced changes of the transcriptome and secretome in Solanum tuberosum leading to resistance against Phytophthora infestans

Phosphite-induced changes of the transcriptome and secretome in Solanum tuberosum leading to resistance against Phytophthora infestans | Host-pathogen interaction | Scoop.it

Background

Potato late blight caused by the oomycete pathogen Phytophthora infestans can lead to immense yield loss. We investigated the transcriptome of Solanum tubersoum (cv. Desiree) and characterized the secretome by quantitative proteomics after foliar application of the protective agent phosphite. We also studied the distribution of phosphite in planta after application and tested transgenic potato lines with impaired in salicylic and jasmonic acid signaling.

Results

Phosphite had a rapid and transient effect on the transcriptome, with a clear response 3?h after treatment. Strikingly this effect lasted less than 24h, whereas protection was observed throughout all time points tested. In contrast, 67 secretome proteins predominantly associated with cell-wall processes and defense changed in abundance at 48 h after treatment. Transcripts associated with defense, wounding, and oxidative stress constituted the core of the phosphite response. We also observed changes in primary metabolism and cell wall-related processes. These changes were shown not to be due to phosphate depletion or acidification caused by phosphite treatment. Of the phosphite-regulated transcripts 40% also changed with ?-aminobutyric acid (BABA) as an elicitor, while the defence gene PR1 was only up-regulated by BABA. Although phosphite was shown to be distributed in planta to parts not directly exposed to phosphite, no protection in leaves without direct foliar application was observed. Furthermore, the analysis of transgenic potato lines indicated that the phosphite-mediated resistance was independent of the plant hormones salicylic and jasmonic acid.

 

Conclusions

Our study suggests that a rapid phosphite-triggered response is important to confer long-lasting resistance against P. infestans and gives molecular understanding of its successful field applications.


Via Christophe Jacquet
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Nari Williams's curator insight, October 6, 2014 6:48 AM

Now to see how these rapid and longer term transcriptional responses compare in woody plants. Given phosphite applications is almost used universally for the control of Phytophthora species, it would be fascinating to see if similar responses are observed across  hosts.

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The next Green Revolution may rely on microbes — NOVA Next | PBS

The next Green Revolution may rely on microbes — NOVA Next | PBS | Host-pathogen interaction | Scoop.it

To feed a planet of 9 billion, scientists are breeding mycorrhizal fungi that promise to boost crop yields by unlocking more nutrients in the soil. Ian Sanders wants to feed the world. A soft-spoken Brit, Sanders studies fungus genetics in a lab at the University of Lausanne in Switzerland. But fear not, he’s not on a mad-scientist quest to get the world to eat protein pastes made from ground-up fungi. Still, he believes—he’s sure—that these microbes will be critical to meeting the world’s future food needs.

Sanders’s eyes widen with delight and almost childlike glee when he talks about a microscopic life form called mycorrhizal fungus, his chosen lifetime research subject. Mycorrhizal fungi live in a tightly wound, mutually beneficial embrace with most plants on the planet. Years of dedication have made Sanders into one of the world’s foremost experts on the genetics of the microbe, and he recently was part of a team that sequenced the first mycorrhizal fungi genome.


Via Francis Martin, Niklaus Grunwald
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The name of the fungus | Science News

The name of the fungus | Science News | Host-pathogen interaction | Scoop.it
A rebellion has broken out against the traditional way of naming species in the peculiar, shape-shifting world of fungi.

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The hybrid nature of the Eukaryota and a consilient view of life on Earth : Nature Reviews Microbiology : Nature Publishing Group

The hybrid nature of the Eukaryota and a consilient view of life on Earth : Nature Reviews Microbiology : Nature Publishing Group | Host-pathogen interaction | Scoop.it

"The origin of the eukaryotic cell, which is known as eukaryogenesis, has puzzled scientists for more than 100 years, and many hypotheses have been proposed. Recent analyses of new data enable the safe elimination of some of these hypotheses, whereas support for other hypotheses has increased. In this Opinion article, we evaluate the available theories for their compatibility with empirical observations and conclude that cellular life consists of two primary, paraphyletic prokaryotic groups and one secondary, monophyletic group that has symbiogenic origins — the eukaryotes."


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MPMI: Deletion of the Phytophthora sojae avirulence gene Avr1d causes gain of virulence on Rps1d (2013)

MPMI: Deletion of the Phytophthora sojae avirulence gene Avr1d causes gain of virulence on Rps1d (2013) | Host-pathogen interaction | Scoop.it

Phytophthora sojae is an oomycete and a pathogen of soybean that causes root rot. During infection P. sojae delivers effector proteins into host cells to foster disease. However, effector-triggered immunity (ETI) results when pathogen factors are recognized by host resistance (R) proteins. Now we have identified the P.sojae Avr1d gene, encoding a predicted effector protein with the amino acid motif Arg-X-Leu-Arg (RXLR). Genetic mapping of 16 different P.sojae isolates and of a segregating F2 population of 40 individuals shows that the predicted RXLR effector gene Avh6 precisely co-segregates with the Avr1d phenotype. Transient expression assays confirm that Avr1d triggers cell death specifically in Rps1d soybean plants. The Avr1d gene is present in P. sojae strains that are avirulent on Rps1d, whereas the gene is deleted from the genome of virulent strains. Two sequence variants of the Avr1d gene encoding different protein products occur in P. sojae strains, but both are recognized by Rps1d and cause ETI. Liposome binding assays show that Avr1d has affinity for phosphatidylinositol 4-phosphate (PtdIns(4)P), and that binding can be disrupted by mutation of lysine residues in the carboxy-terminal effector domain of the protein. The identification of Avr1d aids pathogen diagnostics and soybean cultivar development.


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Phytophthora ramorum in action

This video was captured under the microscope in the Rizzo lab at UC Davis. It shows Phytophthora ramorum sporangia releasing swimming zoospores.
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