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New Phytologist: Characterization of an antimicrobial and phytotoxic ribonuclease secreted by the fungal wheat pathogen Zymoseptoria tritici (2017)

New Phytologist: Characterization of an antimicrobial and phytotoxic ribonuclease secreted by the fungal wheat pathogen Zymoseptoria tritici (2017) | Plants and Microbes | Scoop.it
  •  The fungus Zymoseptoria tritici is the causal agent of Septoria Tritici Blotch (STB) disease of wheat leaves. Zymoseptoria tritici secretes many functionally uncharacterized effector proteins during infection. Here, we characterized a secreted ribonuclease (Zt6) with an unusual biphasic expression pattern.
  • Transient expression systems were used to characterize Zt6, and mutants thereof, in both host and non-host plants. Cell-free protein expression systems monitored the impact of Zt6 protein on functional ribosomes, and in vitroassays of cells treated with recombinant Zt6 determined toxicity against bacteria, yeasts and filamentous fungi.
  • We demonstrated that Zt6 is a functional ribonuclease and that phytotoxicity is dependent on both the presence of a 22-amino-acid N-terminal ‘loop’ region and its catalytic activity. Zt6 selectively cleaves both plant and animal rRNA species, and is toxic to wheat, tobacco, bacterial and yeast cells, but not to Z. tritici itself.
  • Zt6 is the first Z. tritici effector demonstrated to have a likely dual functionality. The expression pattern of Zt6 and potent toxicity towards microorganisms suggest that, although it may contribute to the execution of wheat cell death, it is also likely to have an important secondary function in antimicrobial competition and niche protection.
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Journal of Experimental Botany: Exchanging missives and missiles: the roles of extracellular vesicles in plant–pathogen interactions (2017)

Journal of Experimental Botany: Exchanging missives and missiles: the roles of extracellular vesicles in plant–pathogen interactions (2017) | Plants and Microbes | Scoop.it

This article comments on: Regente M, Pinedo M, San Clemente H, Balliau T, Jamet E, de la Canal L. 2017. Plant extracellular vesicles are incorporated by a fungal

 

Extracellular vesicles (EVs) are secreted by organisms from all forms of life. In the mammalian field they are intensively studied due to their importance in disease and potential for therapeutic use. However, there has been little research in plants and thus the paper byRegente et al. (2017) is a valuable addition to a small but hopefully growing body of data. The authors conducted proteomic analysis on purified sunflower EVs and demonstrated that they are enriched in defence-related proteins. They found that fungal spores treated with fresh EV preparations are damaged and show reduced growth.


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Bridget Barker's curator insight, November 30, 11:12 AM
Curious about EVs in human fungal pathogens...
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MPMI: Phytophthora parasitica effector PpRxLR2 suppresses Nicotiana benthamiana immunity (2017)

MPMI: Phytophthora parasitica effector PpRxLR2 suppresses Nicotiana benthamiana immunity (2017) | Plants and Microbes | Scoop.it

Phytophthora species secrete several classes of effector proteins during interaction with their hosts. These proteins can have multiple functions including modulation of host physiology and immunity. The RxLR effectors have the ability to enter plant cells using the plant machinery. Some of these effectors have been characterized as immunity suppressors; however, very little is known about their functions in the interaction between Phytophthora parasitica and its hosts. Using a bioinformatics pipeline, we have identified 172 candidate RxLR effectors (CREs) in the isolate IAC 01_95 of P. parasitica. Out of these 172 CREs, 93 were found to be also present in other eight genomes of P. parasitica isolated from different hosts and continents. After transcriptomics and gene expression analysis we have found five CREs to be up-regulated in in vitro and in planta samples. Subsequently, we selected three CREs for functional characterization in the model plant Nicotiana benthamiana. We show that PpRxLR2 is able to completely suppress INF-1 induced cell death, whereas PpRxLR3 and PpRxLR5 moderately suppressed N. benthamiana immunity, in a lesser extent manner. Moreover, we confirmed the effector-triggered susceptibility activity of these proteins after transient transformation and infection of N. benthamiana plants. All three CREs enhanced virulence of P. parasitica during the interaction with N. benthamiana. These effectors, in particular PpRxLR2, can be targeted for the development of biotechnology-based control strategies of P. parasitica diseases.


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New Phytologist: Plasmodesmal regulation during plant–pathogen interactions (2017)

New Phytologist: Plasmodesmal regulation during plant–pathogen interactions (2017) | Plants and Microbes | Scoop.it

Plasmodesmata (PD) are plasma membrane-lined pores that connect neighbouring plant cells, bridging the cell wall and establishing cytoplasmic and membrane continuity between cells. PD are dynamic structures regulated by callose deposition in a variety of stress and developmental contexts. This process crudely controls the aperture of the pore and thus the flux of molecules between cells. During pathogen infection, plant cells initiate a range of immune responses and it was recently identified that, following perception of fungal and bacterial pathogens, plant cells initially close their PD. Systemic defence responses depend on the spread of signals between cells, raising questions about whether PD are in different functional states during different immune responses. It is well established that viral pathogens exploit PD to spread between cells, but it has more recently been identified that protein effectors secreted by fungal pathogens can spread between host cells via PD. It is possible that many classes of pathogens specifically target PD to aid infection, which would infer antagonistic regulation of PD by host and pathogen. How PD regulation benefits both host immune responses and pathogen infection is an important question and demands that we examine the multicellular nature of plant–pathogen interactions.

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New Phytologist: Effectors involved in fungal–fungal interaction lead to a rare phenomenon of hyperbiotrophy in the tritrophic system biocontrol agent–powdery mildew–plant (2017)

New Phytologist: Effectors involved in fungal–fungal interaction lead to a rare phenomenon of hyperbiotrophy in the tritrophic system biocontrol agent–powdery mildew–plant (2017) | Plants and Microbes | Scoop.it
  • Tritrophic interactions involving a biocontrol agent, a pathogen and a plant have been analyzed predominantly from the perspective of the biocontrol agent. We have conducted the first comprehensive transcriptomic analysis of all three organisms in an effort to understand the elusive properties of Pseudozyma flocculosa in the context of its biocontrol activity against Blumeria graminis f.sp. hordei as it parasitizes Hordeum vulgare.
  • After inoculation of P. flocculosa, the tripartite interaction was monitored over time and samples collected for scanning electron microscopy and RNA sequencing.
  • Based on our observations, P. flocculosa indirectly parasitizes barley, albeit transiently, by diverting nutrients extracted by B. graminis from barley leaves through a process involving unique effectors. This brings novel evidence that such molecules can also influence fungal–fungal interactions. Their release is synchronized with a higher expression of powdery mildew haustorial effectors, a sharp decline in the photosynthetic machinery of barley and a developmental peak in P. flocculosa. The interaction culminates with a collapse of B. graminis haustoria, thereby stopping P. flocculosa growth, as barley plants show higher metabolic activity.
  • To conclude, our study has uncovered a complex and intricate phenomenon, described here as hyperbiotrophy, only achievable through the conjugated action of the three protagonists.
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New Phytologist: Salicylic acid‐dependent immunity contributes to resistance against Rhizoctonia solani, a necrotrophic fungal agent of sheath blight, in rice and Brachypodium distachyon (2017)

New Phytologist: Salicylic acid‐dependent immunity contributes to resistance against Rhizoctonia solani, a necrotrophic fungal agent of sheath blight, in rice and Brachypodium distachyon (2017) | Plants and Microbes | Scoop.it

 

  • Rhizoctonia solani is a soil-borne fungus causing sheath blight. In consistent with its necrotrophic life style, no rice cultivars fully resistant to R. solani are known, and agrochemical plant defense activators used for rice blast, which upregulate a phytohormonal salicylic acid (SA)-dependent pathway, are ineffective towards this pathogen. As a result of the unavailability of genetics, the infection process of R. solaniremains unclear.
  • We used the model monocotyledonous plants Brachypodium distachyon and rice, and evaluated the effects of phytohormone-induced resistance to R. solani by pharmacological, genetic and microscopic approaches to understand fungal pathogenicity.
  • Pretreatment with SA, but not with plant defense activators used in agriculture, can unexpectedly induce sheath blight resistance in plants. SA treatment inhibits the advancement of R. solani to the point in the infection process in which fungal biomass shows remarkable expansion and specific infection machinery is developed. The involvement of SA in R. solani resistance is demonstrated by SA-deficient NahGtransgenic rice and the sheath blight-resistant B. distachyon accessions, Bd3-1 and Gaz-4, which activate SA-dependent signaling on inoculation.
  • Our findings suggest a hemi-biotrophic nature of R. solani, which can be targeted by SA-dependent plant immunity. Furthermore, B. distachyon provides a genetic resource that can confer disease resistance against R. solani to plants.

 

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bioRxiv: The plant calcium-dependent protein kinase CPK3 phosphorylates REM1.3 to restrict viral infection (2017)

bioRxiv: The plant calcium-dependent protein kinase CPK3 phosphorylates REM1.3 to restrict viral infection (2017) | Plants and Microbes | Scoop.it

Plants respond to pathogens through dynamic regulation of plasma membrane-bound signaling pathways. To date, how the plant plasma membrane is involved in responses to viruses is mostly unknown. Here, we show that plant cells sense the Potato virus X (PVX) COAT PROTEIN and TRIPLE GENE BLOCK 1 proteins and subsequently trigger the activation of a membrane-bound calcium-dependent kinase. We show that the Arabidopsis thaliana CALCIUM-DEPENDENT PROTEIN KINASE 3-interacts with group 1 REMORINs in vivo, phosphorylates the intrinsically disordered N-terminal domain of the Group 1 REMORIN REM1.3, and restricts PVX cell-to-cell movement. REM1.3's phospho-status defines its plasma membrane nanodomain organization and is crucial for REM1.3-dependent restriction of PVX cell-to-cell movement by regulation of callose deposition at plasmodesmata. This study unveils plasma membrane nanodomain-associated molecular events underlying the plant immune response to viruses.


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The Sainsbury Lab's curator insight, October 23, 5:16 AM
Plants respond to pathogens through dynamic regulation of plasma membrane-bound signaling pathways. To date, how the plant plasma membrane is involved in responses to viruses is mostly unknown. Here, we show that plant cells sense the Potato virus X (PVX) COAT PROTEIN and TRIPLE GENE BLOCK 1 proteins and subsequently trigger the activation of a membrane-bound calcium-dependent kinase. We show that the Arabidopsis thaliana CALCIUM-DEPENDENT PROTEIN KINASE 3-interacts with group 1 REMORINs in vivo, phosphorylates the intrinsically disordered N-terminal domain of the Group 1 REMORIN REM1.3, and restricts PVX cell-to-cell movement. REM1.3's phospho-status defines its plasma membrane nanodomain organization and is crucial for REM1.3-dependent restriction of PVX cell-to-cell movement by regulation of callose deposition at plasmodesmata. This study unveils plasma membrane nanodomain-associated molecular events underlying the plant immune response to viruses.
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Trends in Plant Science: Dancing with the Stars: An Asterid NLR Family (2017)

Trends in Plant Science: Dancing with the Stars: An Asterid NLR Family (2017) | Plants and Microbes | Scoop.it

Wu and co-workers show how a network of sensor and helper NOD-like receptor proteins (NLRs) act together to confer robust resistance to diverse plant pathogens.

Plants engage with a plethora of potential pathogens but only some of these microbial overtures lead to disease. This is due to a highly successful system of innate immune receptors that quickly identify the invader and halt its progress. Wu et al. [1] now describe new insights into the molecular choreography of plant immune receptors.

 

Our understanding of these dances began with a simple two-step. There are two partners involved: a Resistance (R) gene in the host and an Avirulence (Avr) gene in the pathogen. They dance a dance according to the gene-for-gene model and resistance is manifest only if both partners are present [2]. The simplest interpretation of the gene-for-gene model is that the R gene encodes a receptor for the product of the Avr gene [3]. In fact, most R genes encode NOD-like receptors (NLRs) that pair a central nucleotide binding domain with C-terminal leucine rich repeats (NB-LRR proteins) [4]. On the other side, most Avr genes encode effectors that are secreted by pathogens to maintain virulence by strategic manipulation of host targets. As LRRs are receptor moieties in other proteins, early models posited them as receptor domains for effectors in a direct interaction, and this simple model holds true for some resistances [5].

 

Along the way, it transpired that more sophisticated models groove to a different beat. For instance, many NLRs recognise changes induced in another host target protein that is modified enzymatically by pathogen effector (Avr) proteins [6]. Examples are also known in which decoy proteins mimic such host target proteins and facilitate recognition by NLRs [7]. Effector decoys can also be provided in cis as a fusion with the NB-LRR moieties [8]. Some NLRs dance solo, but others need two to tango. In this molecular pas-de-deux, one NLR partner is the sensor that interacts with an effector, and the other is a helper that stimulates downstream signal transduction events. These pairs interact physically, and strikingly, are typically co-located genomically in a tail-to-tail arrangement (Figure 1) [9].
 
Sensor-helper relationships also occur between non-linked NLR genes. A widespread class of NLRs called CCR proteins typified by the Nicotiana benthamiana N-required gene 1 (NRG1) and Arabidopsis activated disease resistance gene 1 (ADR1) proteins are needed for a number of sensor NLRs that recognise diverse pathogens [10]. However in this case no contact between sensor and helper has been reported. An analogous situation exists in the Solanaceae, the nightshade family, which includes tomato, eggplant and tobacco. Here a family of NLRs called NRCs (NLR required for cell death), are essential for the function of a range of sensor NLRs [11, 12]. Wu and colleagues now flesh out the details of a network of sensors and helpers in Solanaceae that may enhance the robustness of immunity signalling pathways [1].

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Molecular Plant Pathology: Plum pox virus capsid protein suppresses plant pathogen-associated molecular pattern (PAMP)-triggered immunity (2016)

Molecular Plant Pathology: Plum pox virus capsid protein suppresses plant pathogen-associated molecular pattern (PAMP)-triggered immunity (2016) | Plants and Microbes | Scoop.it

The perception of pathogen-associated molecular patterns (PAMPs) by immune receptors launches defence mechanisms referred to as PAMP-triggered immunity (PTI). Successful pathogens must suppress PTI pathways via the action of effectors to efficiently colonize their hosts. So far, plant PTI has been reported to be active against most classes of pathogens, except viruses, although this defence layer has been hypothesized recently as an active part of antiviral immunity which needs to be suppressed by viruses for infection success. Here, we report that Arabidopsis PTI genes are regulated upon infection by viruses and contribute to plant resistance to Plum pox virus (PPV). Our experiments further show that PPV suppresses two early PTI responses, the oxidative burst and marker gene expression, during Arabidopsis infection. In planta expression of PPV capsid protein (CP) was found to strongly impair these responses in Nicotiana benthamiana and Arabidopsis, revealing its PTI suppressor activity. In summary, we provide the first clear evidence that plant viruses acquired the ability to suppress PTI mechanisms via the action of effectors, highlighting a novel strategy employed by viruses to escape plant defences.

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bioRxiv: Chemosensory proteins in the CSP4 clade evolved as plant immunity suppressors before two suborders of plant-feeding hemipteran insects diverged (2017)

bioRxiv: Chemosensory proteins in the CSP4 clade evolved as plant immunity suppressors before two suborders of plant-feeding hemipteran insects diverged (2017) | Plants and Microbes | Scoop.it

Chemosensory proteins (CSPs) are small globular proteins with hydrophobic binding pockets that have a role in detection of chemicals, regulation of development and growth and host seeking behaviour and feeding of arthropods. Here, we show that a CSP has evolved to modulate plant immune responses. Firstly, we found that the green peach aphid Myzus persicae CSP Mp10, which is delivered into the cytoplasm of plant cells, suppresses the reactive oxygen species (ROS) bursts to both aphid and bacterial elicitors in Arabidopsis thaliana and Nicotiana benthamiana. In contrast, other CSPs, including MpOS-D1, do not have this ROS suppression activity. Aphid RNA interference studies demonstrated that Mp10 modulates the first layer of the plant defence response, specifically the BAK1 pathway. Alignment of CSPs from multiple aphid species showed that Mp10 homologues uniquely have tyrosine (Y40) and tryptophan (W120) flanking the central binding region. Exchange of aromatic residues between Mp10 and MpOS-D1 showed a gain of ROS activity of MpOS-D1 and loss of this activity of Mp10. We identified Mp10 homologs in diverse plant-sucking insect species, including aphids, whiteflies, psyllids and leafhoppers, but not in other insect species, including blood-feeding hemipteran insects. Moreover, the positions of Y and W residues are conserved among these Mp10 homologs, which we found also suppress plant ROS. Together, these data and phylogenetic analyses provides evidence that an ancestral Mp10-like sequence acquired plant ROS suppression activity via gain-of-function mutations before the divergence of plant-sucking insect species over 250 million years ago.

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bioRxiv: Plant genes influence microbial hubs that shape beneficial leaf communities (2017)

bioRxiv: Plant genes influence microbial hubs that shape beneficial leaf communities (2017) | Plants and Microbes | Scoop.it

Although the complex interactions between hosts and microbial associates are increasingly well documented, we still know little about how and why hosts shape microbial communities in nature. We characterized the leaf microbiota within 200 clonal accessions in eight field experiments and detected effects of both local environment and host genotype on community structure. Within environments, hosts′ genetics preferentially associate with a core of ubiquitous microbial hubs that, in turn, structure the community. These microbial hubs correlate with host performance, and a GWAS revealed strong candidate genes for the host factors impacting heritable hubs. Our results reveal how selection may act to enhance fitness through microbial associations and bolster the possibility of enhancing crop performance through these host factors.

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Nature Plants: The pattern-recognition receptor CORE of Solanaceae detects bacterial cold-shock protein (2017)

Nature Plants: The pattern-recognition receptor CORE of Solanaceae detects bacterial cold-shock protein (2017) | Plants and Microbes | Scoop.it

Plants and animals recognize microbial invaders by detecting microbe-associated molecular patterns (MAMPs) by cell surface receptors. Many plant species of the Solanaceae family detect the highly conserved nucleic acid binding motif RNP-1 of bacterial cold-shock proteins (CSPs), represented by the peptide csp22, as a MAMP. Here, we exploited the natural variation in csp22 perception observed between cultivated tomato (Solanum lycopersicum) and Solanum pennellii to map and identify the leucine-rich repeat (LRR) receptor kinase CORE (cold shock protein receptor) of tomato as the specific, high-affinity receptor site for csp22. Corroborating its function as a genuine receptor, heterologous expression of CORE in Arabidopsis thaliana conferred full sensitivity to csp22 and, importantly, it also rendered these plants more resistant to infection by the bacterial pathogen Pseudomonas syringaepv. tomato DC3000. Our study also confirms the biotechnological potential of enhancing plant immunity by interspecies transfer of highly effective pattern-recognition receptors such as CORE to different plant families.

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PNAS: Disease resistance through impairment of α-SNAP–NSF interaction and vesicular trafficking by soybean Rhg1 (2017)

PNAS: Disease resistance through impairment of α-SNAP–NSF interaction and vesicular trafficking by soybean Rhg1 (2017) | Plants and Microbes | Scoop.it

The Rhg1 resistance locus of soybean helps control one of the most damaging diseases in world agriculture. We found that Rhg1 (resistance to Heterodera glycines 1)-mediated resistance utilizes an unusual mechanism. Resistant soybeans carry a dysfunctional variant of the housekeeping protein α-SNAP [soluble NSF (N-ethylmaleimide–sensitive factor) attachment protein]. Rhg1 resistance-type α-SNAPs interact poorly with NSF and disrupt vesicle trafficking. High levels of resistance-type α-SNAPs interfere with wild-type α-SNAP activities, yet are functionally balanced in most tissues by sufficient wild-type α-SNAP levels. However, the biotrophic plant–pathogen interface is disabled by localized hyperaccumulation of resistance-type α-SNAPs. This study suggests a paradigm of resistance conferred by a dysfunctional version of a core cellular housekeeping protein.

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New Phytologist: Sugar flux and signaling in plant‐microbe interactions (2017)

New Phytologist: Sugar flux and signaling in plant‐microbe interactions (2017) | Plants and Microbes | Scoop.it

Plant breeders have developed crop plants that are resistant to pests, but the continual evolution of pathogens creates the need to iteratively develop new control strategies. Molecular tools have allowed us to gain deep insights into disease responses, allowing for more efficient, rational engineering of crops that are more robust or resistant to a greater number of pathogen variants. Here we describe the roles in disease progress of SWEET and STP transporters, which are membrane proteins that mediate transport of sugars across the plasma membrane. We discuss how these transporters may enhance or restrict disease through controlling the level of nutrients provided to pathogens and if the transporters play a role in sugar signaling for disease resistance. This review indicates open questions that require further research and proposes the use of genome editing technologies for engineering disease resistance.


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MPMI: Lessons in Effector and NLR Biology of Plant-Microbe Systems (2017)

MPMI: Lessons in Effector and NLR Biology of Plant-Microbe Systems (2017) | Plants and Microbes | Scoop.it

A diversity of plant-associated organisms secrete effectors—proteins and metabolites that modulate plant physiology to favor host infection and colonization. However, effectors can also activate plant immune receptors, notably nucleotide-binding domain and leucine-rich repeat region (NLR)-containing proteins, enabling plants to fight off invading organisms. This interplay between effectors, their host targets, and the matching immune receptors is shaped by intricate molecular mechanisms and exceptionally dynamic coevolution. In this article, we focus on three effectors, AVR-Pik, AVR-Pia, and AVR-Pii, from the rice blast fungus Magnaporthe oryzae (syn. Pyricularia oryzae), and their corresponding rice NLR immune receptors, Pik, Pia, and Pii, to highlight general concepts of plant-microbe interactions. We draw 12 lessons in effector and NLR biology that have emerged from studying these three little effectors and are broadly applicable to other plant-microbe systems.

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New Phytologist: Multiple strategies for pathogen perception by plant immune receptors (2017)

New Phytologist: Multiple strategies for pathogen perception by plant immune receptors (2017) | Plants and Microbes | Scoop.it

Plants have evolved a complex immune system to protect themselves against phytopathogens. A major class of plant immune receptors called nucleotide-binding domain and leucine-rich repeat-containing proteins (NLRs) is ubiquitous in plants and is widely used for crop disease protection, making these proteins critical contributors to global food security. Until recently, NLRs were thought to be conserved in their modular architecture and functional features. Investigation of their biochemical, functional and structural properties has revealed fascinating mechanisms that enable these proteins to perceive a wide range of pathogens. Here, I review recent insights demonstrating that NLRs are more mechanistically and structurally diverse than previously thought. I also discuss how these findings provide exciting future prospects to improve plant disease resistance.

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Bridget Barker's curator insight, November 21, 9:22 AM
Always thinking about links between animal and plant pathogens
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bioRxiv: Arabidopsis HIPP27 is a host susceptibility gene for the beet cyst nematode Heterodera schachtii (2017)

bioRxiv: Arabidopsis HIPP27 is a host susceptibility gene for the beet cyst nematode Heterodera schachtii (2017) | Plants and Microbes | Scoop.it

Sedentary plant-parasitic cyst nematodes are obligate biotrophs that infect the roots of their host plant. Their parasitism is based on modification of infected root cells to form a hypermetabolic syncytium from which the nematodes draw their nutrients. The aim of this study was to identify nematode susceptibility genes in Arabidopsis thaliana and to characterize their roles in supporting the parasitism of Heterodera schachtii. By selecting genes that were most strongly upregulated in response to cyst nematode infection, we identified HIPP27 (HEAVY METAL-ASSOCIATED ISOPRENYLATED PLANT PROTEIN 27) as a host susceptibility factor required for beet cyst nematode infection and development. Detailed expression analysis revealed that HIPP27 is a cytoplasmic protein and that HIPP27 is strongly expressed in leaves, young roots and nematode-induced syncytia. Loss-of-function Arabidopsis hipp27 mutants exhibited severely reduced susceptibility to Heterodera schachtii and abnormal starch accumulation in syncytial and peridermal plastids. Our results suggest that HIPP27 is a susceptibility gene in Arabidopsis whose loss-of-function reduces plant susceptibility to cyst nematode infection without increasing susceptibility to other pathogens or negatively affecting plant phenotype.

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Current Opinion in Plant Biology: Autophagy as a mediator of life and death in plants (2017)

Current Opinion in Plant Biology: Autophagy as a mediator of life and death in plants (2017) | Plants and Microbes | Scoop.it
Autophagy is a major pathway for degradation and recycling of cytoplasmic material, including individual proteins, aggregates, and entire organelles. Autophagic processes serve mainly survival functions in cellular homeostasis, stress adaptation and immune responses but can also have death-promoting activities in different eukaryotic organisms. In plants, the role of autophagy in the regulation of programmed cell death (PCD) remained elusive and a subject of debate. More recent evidence, however, has resulted in the consensus that autophagy can either promote or restrict different forms of PCD. Here, we present latest advances in understanding the molecular mechanisms and functions of plant autophagy and discuss their implications for life and death decisions in the context of developmental and pathogen-induced PCD.

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Trends in Plant Science: Balancing Immunity and Yield in Crop Plants (2017)

Trends in Plant Science: Balancing Immunity and Yield in Crop Plants (2017) | Plants and Microbes | Scoop.it

Crop diseases cause enormous yield losses and threaten global food[ED1] security. The use of highly resistant cultivars can effectively control plant diseases, but in crops, genetic immunity to disease often comes with an unintended reduction in growth and yield. Here, we review recent advances in understanding how nucleotide-binding domain, leucine-rich repeat (NLR) receptors and cell wall-associated kinase (WAK) proteins function in balancing immunity and yield. We also discuss the role of plant hormones and transcription factors in regulating the trade-offs between plant growth and immunity. Finally, we describe how a novel mechanism of translational control of defense proteins can enhance immunity without the reduction in fitness.

 

  • High yield and immunity to pathogens are important objectives in plant breeding. However, plant growth and immunity pathways are intertwined and usually antagonistic.
  • Hormones are important for plant growth; however, activation of immunity redirects and initiates hormone signaling that can impair plant growth.
  • Transcription factors act as molecular integrators to regulate the trade-offs between immunity and growth. NLR and WAK immune receptors play dual roles in immunity and yield.
  • Pathogen-inducible translational control strategies can enhance plant immunity without fitness costs.
  • New breeding strategies should be developed to enhance immunity without sacrificing fitness and yield.
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bioRxiv: Phytophthora palmivora establishes tissue-specific intracellular infection structures in the earliest divergent land plant lineage (2017)

bioRxiv: Phytophthora palmivora establishes tissue-specific intracellular infection structures in the earliest divergent land plant lineage (2017) | Plants and Microbes | Scoop.it

The expansion of plants onto land was a formative event that brought forth profound changes to the Earth's geochemistry and biota. Filamentous eukaryotic microbes developed the ability to colonize plant tissues early during the evolution of land plants, as demonstrated by intimate symbiosis-like associations in >400 million-year-old fossils. However, the degree to which filamentous microbes establish pathogenic interactions with early divergent land plants is unclear. Here, we demonstrate that the broad host-range oomycete pathogen Phytophthora palmivora colonizes liverworts, the earliest divergent land plant lineage. We show that P. palmivora establishes a complex tissue-specific interaction with Marchantia polymorpha, where it completes a full infection cycle within air chambers of the dorsal photosynthetic layer. Remarkably, P. palmivora invaginates M. polymorpha cells with haustoria-like structures that accumulate host cellular trafficking machinery and the membrane-syntaxin MpSYP13B but not the related MpSYP13A. Our results indicate that the intracellular accommodation of filamentous microbes is an ancient plant trait that is successfully exploited by pathogens like P. palmivora.


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Philip Carella's curator insight, September 15, 1:28 PM

Our new pre-print! Happy to receive any feedback. 

Philip Carella's curator insight, September 15, 1:29 PM

Our new pre-print! Happy to receive any feedback

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Molecular Plant Pathology: Rmg8 and Rmg7, wheat genes for resistance to the wheat blast fungus, recognize the same avirulence gene AVR‐Rmg8 (2017)

Molecular Plant Pathology: Rmg8 and Rmg7, wheat genes for resistance to the wheat blast fungus, recognize the same avirulence gene AVR‐Rmg8 (2017) | Plants and Microbes | Scoop.it

Rmg8 and Rmg7 are genes for resistance to the wheat blast fungus (Pyricularia oryzae) located on 2B chromosome in hexaploid wheat and 2A chromosome in tetraploid wheat, respectively. AVR-Rmg8, an avirulence gene corresponding to Rmg8, was isolated from a wheat blast isolate through map-based strategy. The cloned fragment encoded a small protein containing a putative signal peptide. AVR-Rmg8 was recognized not only by Rmg8 but also by Rmg7, suggesting that these two resistance genes are equivalent to a single gene from the viewpoint of resistance breeding. This article is protected by copyright. All rights reserved.

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bioRxiv: MicroRNAs from the parasitic plant Cuscuta campestris target host messenger RNAs (2017)

bioRxiv: MicroRNAs from the parasitic plant Cuscuta campestris target host messenger RNAs (2017) | Plants and Microbes | Scoop.it

Dodders (Cuscuta spp.) are obligate parasitic plants that obtain water and nutrients from the stems of host plants via specialized feeding structures called haustoria. Dodder haustoria facilitate bi-directional movement of viruses, proteins, and mRNAs between host and parasite, but the functional effects of these movements are not clear. Here we show that C. campestris haustoria accumulate high levels of many novel microRNAs (miRNAs) while parasitizing Arabidopsis thaliana hosts. Many of these miRNAs are 22 nts long, a usually rare size of plant miRNA associated with amplification of target silencing through secondary small interfering RNA (siRNA) production. Several A. thaliana mRNAs are targeted by C. campestris 22 nt miRNAs during parasitism, resulting in mRNA cleavage, high levels of secondary siRNA production, and decreased mRNA accumulation levels. Hosts with a mutation in the target SIEVE ELEMENT OCCLUSION RELATED 1 (SEOR1) supported significantly higher growth of C. campestris. Homologs of target mRNAs from diverse plants also have predicted target sites to induced C. campestris miRNAs, and several of the same miRNAs are expressed when C. campestris parasitizes a second host, Nicotiana benthamiana. These data show that C. campestris miRNAs act as trans-species regulators of host gene expression, and suggest that they may act as virulence factors during parasitism.

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bioRxiv: A plant receptor-like kinase promotes cell-to-cell spread of RNAi and is targeted by a virus (2017)

bioRxiv: A plant receptor-like kinase promotes cell-to-cell spread of RNAi and is targeted by a virus (2017) | Plants and Microbes | Scoop.it

RNA interference (RNAi) in plants can move from cell to cell, allowing for systemic spread of an anti-viral immune response. How this cell-to-cell spread of silencing is regulated is currently unknown. Here, we describe that the C4 protein from Tomato yellow leaf curl virus has the ability to inhibit the intercellular spread of RNAi. Using this viral protein as a probe, we have identified the receptor-like kinase (RLK) BARELY ANY MERISTEM 1 (BAM1) as a positive regulator of the cell-to-cell movement of RNAi, and determined that BAM1 and its closest homologue, BAM2, play a redundant role in this process. C4 interacts with the intracellular domain of BAM1 and BAM2 at the plasma membrane and plasmodesmata, the cytoplasmic connections between plant cells, interfering with the function of these RLKs in the cell-to-cell spread of RNAi. Our results identify BAM1 as an element required for the cell-to-cell spread of RNAi and highlight that signalling components have been co-opted to play multiple functions in plants.

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Genome Biology: MAPK-triggered chromatin reprogramming by histone deacetylase in plant innate immunity (2017)

Genome Biology: MAPK-triggered chromatin reprogramming by histone deacetylase in plant innate immunity (2017) | Plants and Microbes | Scoop.it

Background. Microbial-associated molecular patterns activate several MAP kinases, which are major regulators of the innate immune response in Arabidopsis thaliana that induce large-scale changes in gene expression. Here, we determine whether microbial-associated molecular pattern-triggered gene expression involves modifications at the chromatin level.

 

Results. Histone acetylation and deacetylation are major regulators of microbial-associated molecular pattern-triggered gene expression and implicate the histone deacetylase HD2B in the reprogramming of defence gene expression and innate immunity. The MAP kinase MPK3 directly interacts with and phosphorylates HD2B, thereby regulating the intra-nuclear compartmentalization and function of the histone deacetylase.

 

Conclusions. By studying a number of gene loci that undergo microbial-associated molecular pattern-dependent activation or repression, our data reveal a mechanistic model for how protein kinase signaling directly impacts chromatin reprogramming in plant defense.

 

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