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PLOS Pathogens: Ustilago maydis: Dissecting the Molecular Interface between Pathogen and Plant

PLOS Pathogens: Ustilago maydis: Dissecting the Molecular Interface between Pathogen and Plant | Plant-Microbe Interaction | Scoop.it
Fungal diseases of plants represent one of the most eminent threats to agriculture. Given the food needs of a growing world population and that more and more crops are devoted to fuel production, the necessity to develop crops with better resistance to disease is increasing. To accomplish this, the mechanisms that plant pathogenic fungi use to colonize plants need to be elucidated. As of now, there are only few examples/models in which this can be done on a functional, genome-wide level, taking into account both the pathogen and its host plant [1]. The fungus Ustilago maydis (U. maydis) is one of these examples. It is a member of the smut fungi: a large group of parasites infecting mostly grasses, including several important crop plants such as maize (Figure 1B), wheat, barley, and sugar cane. Smut fungi are biotrophs, i.e., parasites that need the living host plant to complete their sexual life cycle [2], [3]. They do not establish prominent feeding structures like the related, haustoria-forming rust fungi. During penetration, the host plasma membrane invaginates and completely encases the intracellular hyphae (Figure 1A), establishing an extended interaction zone [4] mediating the exchange of molecules between fungus and host. In contrast to most smut fungi that cause a systemic infection, remaining symptomless until the plant flowers, U. maydis can infect all above-ground parts of the maize plant but fails to spread systemically. U. maydis induces local tumors in which spores develop (Figure 1B) – a unique feature that allows detection of symptoms in corn seedlings less than a week after syringe infection with high levels of inoculum. This, together with the toolbox developed for reverse genetics, cell biology, and functional studies, has contributed to its status as a model for biotrophic basidiomycete fungi [5]. Here the current level of our understanding of the elaborate molecular crosstalk between U. maydis and its host plant will be discussed.

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Systematic characterization of the bZIP transcription factor gene family in the rice blast fungus, Magnaporthe oryzae

Systematic characterization of the bZIP transcription factor gene family in the rice blast fungus, Magnaporthe oryzae | Plant-Microbe Interaction | Scoop.it

In this study the 22 Magnaporthe oryzae genes encoding bZIP transcription factors were systematically characterized. Phylogenetic analysis of fungal bZIP TFs revealed that 7 MobZIPs are Magnaporthe-specific while others belongs to 15 clades of orthologous Ascomycota genes. Expression patterns of MobZIPs under various conditions showed that they are highly stress-responsive. We generated deletion mutants for 13 MobZIPs: 9 with orthologs in other fungal species and 4 Magnaporthe-specific ones. Seven of them exhibited defects in mycelial growth, development, and/or pathogenicity. Consistent with the conserved functions of the orthologs, MobZIP22 and MobZIP13 played a role in sulfur metabolism and iron homeostasis, respectively. Along with MobZIP22 and MobZIP13, one Magnaporthe-specific gene, MobZIP11 is essential for pathogenicity in a ROS-dependent manner. 


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The effective papilla hypothesis -

The effective papilla hypothesis - | Plant-Microbe Interaction | Scoop.it
Keywords:

arabinoxylan;
callose;
cell wall apposition;
cellulose;
papilla;
penetration resistance;
powdery mildew

In phytopathology, little is understood about what stops a parasitic fungus from penetrating a host cell wall. Plants often form cell wall appositions, called papillae, in response to fungal attempts to penetrate their cell wall, and the molecular composition of these papillae differs from that of primary and secondary cell walls. However, we do not know whether altered cell wall composition is critical for restricting penetration. In this issue of New Phytologist, Chowdhury et al. (pp. 650–660) used the model interaction of barley (Hordeum vulgare) with the barley-adapted grass powdery mildew fungus (Blumeria graminis f. sp. hordei) to study this phenomenon. The work by Chowdhury et al. significantly adds to our understanding of what distinguishes a papilla, in which a fungal penetration attempt failed, from a penetrated papilla. Using an immunohistochemical approach, Chowdhury et al. identified that callose, arabinoxylans, and cellulose are significantly enriched in nonpenetrated papillae (NPP) over penetrated papillae (PP) and showed that papilla composition is determined in a cell-autonomous fashion. This opens up new possibilities for experimental designs that may help to answer the question of whether papillary cell wall polymers contribute significantly to penetration resistance.

Via Christophe Jacquet
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Threonine deaminase MoIlv1 is important for conidiogenesis and pathogenesis in the rice blast fungus Magnaporthe oryzae

Threonine deaminase MoIlv1 is important for conidiogenesis and pathogenesis in the rice blast fungus Magnaporthe oryzae | Plant-Microbe Interaction | Scoop.it

MoIlv1 is important for conidial morphology, asexual development, penetration and pathogenicity inM. oryzae.

The PALP, DEH1 and DEH2 domain are/is required for the full function of MoIlv1 during growth, development and pathogenicity


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Nucleotide-binding oligomerization domain-like receptor cooperativity in effector-triggered immunity

Nucleotide-binding oligomerization domain-like receptor cooperativity in effector-triggered immunity | Plant-Microbe Interaction | Scoop.it

Intracellular nucleotide-binding oligomerization domain (NOD)-like receptors (NLRs) are basic elements of innate immunity in plants and animals. Whereas animal NLRs react to conserved microbe- or damage-associated molecular patterns, plant NLRs intercept the actions of diverse pathogen virulence factors (effectors). In this review, we discuss recent genetic and molecular evidence for functional NLR pairs, and discuss the significance of NLR self-association and heteromeric NLR assemblies in the triggering of downstream signaling pathways. We highlight the versatility and impact of cooperating NLR pairs that combine pathogen sensing with the initiation of defense signaling in both plant and animal immunity. We propose that different NLR receptor molecular configurations provide opportunities for fine-tuning resistance pathways and enhancing the host's pathogen recognition spectrum to keep pace with rapidly evolving microbial populations.

  


Via Suayib Üstün
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Expression Profiling during Arabidopsis/Downy Mildew Interaction Reveals a Highly-Expressed Effector That Attenuates Responses to Salicylic Acid

Expression Profiling during Arabidopsis/Downy Mildew Interaction Reveals a Highly-Expressed Effector That Attenuates Responses to Salicylic Acid | Plant-Microbe Interaction | Scoop.it
Plants have evolved strong innate immunity mechanisms, but successful pathogens evade or suppress plant immunity via effectors delivered into the plant cell. Hyaloperonospora arabidopsidis (Hpa) causes downy mildew on Arabidopsis thaliana, and a genome sequence is available for isolate Emoy2. Here, we exploit the availability of genome sequences for Hpa and Arabidopsis to measure gene-expression changes in both Hpa and Arabidopsis simultaneously during infection. Using a high-throughput cDNA tag sequencing method, we reveal expression patterns of Hpa predicted effectors and Arabidopsis genes in compatible and incompatible interactions, and promoter elements associated with Hpa genes expressed during infection. By resequencing Hpa isolate Waco9, we found it evades Arabidopsis resistance gene RPP1 through deletion of the cognate recognized effector ATR1. Arabidopsis salicylic acid (SA)-responsive genes including PR1 were activated not only at early time points in the incompatible interaction but also at late time points in the compatible interaction. By histochemical analysis, we found that Hpa suppresses SA-inducible PR1 expression, specifically in the haustoriated cells into which host-translocated effectors are delivered, but not in non-haustoriated adjacent cells. Finally, we found a highly-expressed Hpa effector candidate that suppresses responsiveness to SA. As this approach can be easily applied to host-pathogen interactions for which both host and pathogen genome sequences are available, this work opens the door towards transcriptome studies in infection biology that should help unravel pathogen infection strategies and the mechanisms by which host defense responses are overcome.

Via Suayib Üstün
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The brassinosteroid chemical toolbox

The brassinosteroid chemical toolbox | Plant-Microbe Interaction | Scoop.it
Highlights



Brassinosteroid research benefited from several chemical biology approaches.


Small molecules target biosynthesis as well as signaling.


Analogs of brassinolide allowed binding studies and visualization.


Small molecules present large opportunities for future brassinosteroid research.

Chemical biology approaches have been instrumental in understanding the mode of action of brassinosteroids, a group of plant steroid hormones essential for plant development and growth. The small molecules used for such approaches include inhibitors of biosynthetic enzymes and signaling components. Additionally, recent structural data on the brassinosteroid receptor complex together with its ligand brassinolide, the most active brassinosteroid, and knowledge on its different analogs have given us a better view on the recognition of the hormone and signaling initiation. Moreover, a fluorescently labeled brassinosteroid enabled the visualization of the receptor–ligand pair in the cell. Given the insights obtained, small molecules will continue to provide new opportunities for probing brassinosteroid biosynthesis and for unraveling the dynamic and highly interconnected signaling.

Via Christophe Jacquet
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Mary Williams's curator insight, October 15, 7:54 AM

Oh - super review from the Dec 2014 Curr Opin Plant Biol!

I'm reading this on the plane tonight!

Rescooped by Guogen Yang from Plant-microbe interactions (on the plant's side)
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Large-scale transcriptome comparison reveals distinct gene activations in wheat responding to stripe rust and powdery mildew

Large-scale transcriptome comparison reveals distinct gene activations in wheat responding to stripe rust and powdery mildew | Plant-Microbe Interaction | Scoop.it
Background

Stripe rust (Puccinia striiformis f. sp. tritici; Pst) and powdery mildew (Blumeria graminis f. sp. tritici; Bgt) are important diseases of wheat (Triticum aestivum) worldwide. Similar mechanisms and gene transcripts are assumed to be involved in the host defense response because both pathogens are biotrophic fungi. The main objective of our study was to identify co-regulated mRNAs that show a change in expression pattern after inoculation with Pst or Bgt, and to identify mRNAs specific to the fungal stress response.

Results

The transcriptome of the hexaploid wheat line N9134 inoculated with the Chinese Pst race CYR 31 was compared with that of the same line inoculated with Bgt race E09 at 1, 2, and 3 days post-inoculation. Infection by Pst and Bgt affected transcription of 23.8% of all T. aestivum genes. Infection by Bgt triggered a more robust alteration in gene expression in N9134 compared with the response to Pst infection. An array of overlapping gene clusters with distinctive expression patterns provided insight into the regulatory differences in the responses to Bgt and Pst infection. The differentially expressed genes were grouped into seven enriched Kyoto Encyclopedia of Genes and Genomes pathways in Bgt-infected leaves and four pathways in Pst-infected leaves, while only two pathways overlapped. In the plant-pathogen interaction pathway, N9134 activated a higher number of genes and pathways in response to Bgt infection than in response to Pst invasion. Genomic analysis revealed that the wheat genome shared some microbial genetic fragments, which were specifically induced in response to Bgt and Pst infection.

Conclusions

Taken together, our findings indicate that the responses of wheat N9134 to infection by Bgt and Pst shows differences in the pathways and genes activated. The mass sequence data for wheat-fungus interaction generated in this study provides a powerful platform for future functional and molecular research on wheat-fungus interactions.

 

 


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GbWRKY1 mediates plant defense-to-development transition during infection of cotton by Verticillium dahliae by activating JAZ1 expression

Plants have evolved an elaborate signaling network to ensure an appropriate level of immune response to meet the differing demands of developmental processes. Previous research has demonstrated that DELLA proteins physically interact with JAZ1 and dynamically regulate the interaction of the gibberellic acid (GA) and jasmonic acid (JA) signaling pathways. However, whether and how the JAZ1-DELLA regulatory node is regulated at the transcriptional level in plants under normal growth conditions or during pathogen infection is not known. Here, we demonstrate multiple functions of Gossypium barbadense GbWRKY1 in the plant defense response and during development. Although GbWRKY1 expression is induced rapidly by MeJA and infection by Verticillium dahliae, our results show that GbWRKY1 is a negative regulator of the JA-mediated defense response and plant resistance to the pathogens Botrytis cinerea and V. dahliae. Under normal growth conditions, GbWRKY1-overexpressing lines displayed GA-associated phenotypes, including organ elongation and early flowering, coupled with the downregulation of the putative targets of DELLA. We show that the GA-related phenotypes of GbWRKY1-overexpressing plants depend on the constitutive expression of Gossypium hirsutum GhJAZ1. We also show that GhJAZ1 can be trans-activated by GbWRKY1 through TGAC core sequences, and the adjacent sequences of this binding site are essential for binding specificity and affinity to GbWRKY1 as revealed by dual-luciferase reporter assays and electrophoretic mobility shift assays. In summary, our data suggest that GbWRKY1 is a critical regulator mediating the plant defense-to-development transition during V. dahliae infection by activating JAZ1 expression.

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Rescooped by Guogen Yang from MycorWeb Plant-Microbe Interactions
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Origins of major archaeal clades correspond to gene acquisitions from bacteria : Nature

Origins of major archaeal clades correspond to gene acquisitions from bacteria : Nature | Plant-Microbe Interaction | Scoop.it
The mechanisms that underlie the origin of major prokaryotic groups are poorly understood. In principle, the origin of both species and higher taxa among prokaryotes should entail similar mechanisms[mdash]ecological interactions with the environment paired with natural genetic variation involving lineage-specific gene innovations and lineage-specific gene acquisitions. To investigate the origin of higher taxa in archaea, we have determined gene distributions and gene phylogenies for the 267,568 protein-coding genes of 134 sequenced archaeal genomes in the context of their homologues from 1,847 reference bacterial genomes. Archaeal-specific gene families define 13 traditionally recognized archaeal higher taxa in our sample. Here we report that the origins of these 13 groups unexpectedly correspond to 2,264 group-specific gene acquisitions from bacteria. Interdomain gene transfer is highly asymmetric, transfers from bacteria to archaea are more than fivefold more frequent than vice versa. Gene transfers identified at major evolutionary transitions among prokaryotes specifically implicate gene acquisitions for metabolic functions from bacteria as key innovations in the origin of higher archaeal taxa.

Via Francis Martin
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The genetics of monarch butterfly migration and warning colouration : Nature

The genetics of monarch butterfly migration and warning colouration : Nature | Plant-Microbe Interaction | Scoop.it
The monarch butterfly, Danaus plexippus, is famous for its spectacular annual migration across North America, recent worldwide dispersal, and orange warning colouration. Despite decades of study and broad public interest, we know little about the genetic basis of these hallmark traits. Here we uncover the history of the monarch’s evolutionary origin and global dispersal, characterize the genes and pathways associated with migratory behaviour, and identify the discrete genetic basis of warning colouration by sequencing 101 Danaus genomes from around the globe. The results rewrite our understanding of this classic system, showing that D. plexippus was ancestrally migratory and dispersed out of North America to occupy its broad distribution. We find the strongest signatures of selection associated with migration centre on flight muscle function, resulting in greater flight efficiency among migratory monarchs, and that variation in monarch warning colouration is controlled by a single myosin gene not previously implicated in insect pigmentation.

Via Francis Martin
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Genomics: Of monarchs and migration : Nature

Genomics: Of monarchs and migration : Nature | Plant-Microbe Interaction | Scoop.it

The genomes of 101 monarch butterflies from migratory and resident populations have been sequenced, revealing genes and molecular pathways that underlie insect migration and colouration.

Which evolved first, the temperate migratory populations or the resident tropical groups? For birds, the 'southern home' theory suggests that migratory populations arose from non-migratory tropical populations5. Surprisingly, Zhan and colleagues' analysis of migratory and non-migratory monarchs shows that these butterflies originated in North America, from a migratory ancestor. Tropical groups had reduced genetic diversity compared with their North American relatives, because they have gone through step-wise genetic bottlenecks during their colonization of the tropics, each of which reduced the diversity of their genomes.


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Rescooped by Guogen Yang from Plant Immunity And Microbial Effectors
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Salicylic Acid Regulates Arabidopsis Microbial Pattern Receptor Kinase Levels and Signaling

This work shows that pattern receptors are dynamically regulated by salicylic acid signaling and that pattern receptors are also needed for cell wall-based defense activated by salicylic acid.

Via IPM Lab
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Rescooped by Guogen Yang from Plant-microbe interactions (on the plant's side)
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Frontiers | Rho family GTPase-dependent immunity in plants and animals | Plant Traffic and Transport

Frontiers | Rho family GTPase-dependent immunity in plants and animals | Plant Traffic and Transport | Plant-Microbe Interaction | Scoop.it
In plants, sophisticated forms of immune systems have developed to cope with a variety of pathogens. Accumulating evidence indicates that Rac (also known as Rop), a member of the Rho family of small GTPases, is a key regulator of immunity in plants and animals. Like other small GTPases, Rac/Rop GTPases function as a molecular switch downstream of immune receptors by cycling between GDP-bound inactive and GTP-bound active forms in cells. Rac/Rop GTPases trigger various immune responses, thereby resulting in enhanced disease resistance to pathogens. In this review, we highlight recent studies that have contributed to our current understanding of the Rac/Rop family of GTPases and the upstream and downstream proteins involved in plant immunity. We also compare the features of effector-triggered immunity between plants and animals and discuss the in vivo monitoring of Rac/Rop activation.

Via Christophe Jacquet
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Differential accumulation of callose, arabinoxylan and cellulose in nonpenetrated versus penetrated papillae on leaves of barley infected with Blumeria graminis f. sp. hordei

Differential accumulation of callose, arabinoxylan and cellulose in nonpenetrated versus penetrated papillae on leaves of barley infected with Blumeria graminis f. sp. hordei | Plant-Microbe Interaction | Scoop.it

In plants, cell walls are one of the first lines of defence for protecting cells from successful invasion by fungal pathogens and are a major factor in basal host resistance. For the plant cell to block penetration attempts, it must adapt its cell wall to withstand the physical and chemical forces applied by the fungus.Papillae that have been effective in preventing penetration by pathogens are traditionally believed to contain callose as the main polysaccharide component. Here, we have re-examined the composition of papillae of barley (Hordeum vulgare) attacked by the powdery mildew fungus Blumeria graminis f. sp. hordei (Bgh) using a range of antibodies and carbohydrate-binding modules that are targeted to cell wall polysaccharides.The data show that barley papillae induced during infection with Bgh contain, in addition to callose, significant concentrations of cellulose and arabinoxylan. Higher concentrations of callose, arabinoxylan and cellulose are found in effective papillae, compared with ineffective papillae. The papillae have a layered structure, with the inner core consisting of callose and arabinoxylan and the outer layer containing arabinoxylan and cellulose.The association of arabinoxylan and cellulose with penetration resistance suggests new targets for the improvement of papilla composition and enhanced disease resistance.


Via Christophe Jacquet
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Christophe Jacquet's curator insight, October 17, 7:08 AM

Nice work and great photos!

Rescooped by Guogen Yang from Plant-microbe interaction
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A Unique Plant ESCRT Component, FREE1, Regulates Multivesicular Body Protein Sorting and Plant Growth: Current Biology

A Unique Plant ESCRT Component, FREE1, Regulates Multivesicular Body Protein Sorting and Plant Growth: Current Biology | Plant-Microbe Interaction | Scoop.it
Highlights•FREE1 is a plant-specific and PVC-localized FYVE domain protein binding to PI3P•FREE1 is in a complex with ESCRT-I via a direct interaction with Vps23•FREE1 directly binds to ubiquitin and regulates vacuolar membrane protein sorting•FREE1 is essential for PVC/MVB biogenesis and plant growthSummary

Tight control of membrane protein homeostasis by selective degradation is crucial for proper cell signaling and multicellular organismal development. Membrane proteins destined for degradation, such as misfolded proteins or activated receptors, are usually ubiquitinated and sorted into the intraluminal vesicles (ILVs) of prevacuolar compartments/multivesicular bodies (PVCs/MVBs), which then fuse with vacuoles/lysosomes to deliver their contents to the lumen for degradation by luminal proteases [ 1 ]. The formation of ILVs and the sorting of ubiquitinated membrane cargoes into them are facilitated by the endosomal sorting complex required for transport (ESCRT) machinery [ 2–4 ]. Plants possess most evolutionarily conserved members of the ESCRT machinery but apparently lack orthologs of ESCRT-0 subunits and the ESCRT-I component Mvb12 [ 5–8 ]. Here, we identified a unique plant ESCRT component called FYVE domain protein required for endosomal sorting 1 (FREE1). FREE1 binds to phosphatidylinositol-3-phosphate (PI3P) and ubiquitin and specifically interacts with Vps23 via PTAP-like tetrapeptide motifs to be incorporated into the ESCRT-I complex. Arabidopsis free1 mutant is seedling lethal and defective in the formation of ILVs in MVBs. Consequently, endocytosed plasma membrane (PM) proteins destined for degradation, such as the auxin efflux carrier PIN2 [ 9, 10 ], cannot reach the lumen of the vacuole and mislocalize to the tonoplast. Collectively, our findings provide the first functional characterization of a plant FYVE domain protein, which is essential for plant growth via its role as a unique evolutionary ESCRT component for MVB biogenesis and vacuolar sorting of membrane proteins.


Via Suayib Üstün
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Dissecting the Transcriptional Response to Elicitors in Vitis vinifera Cells

Dissecting the Transcriptional Response to Elicitors in Vitis vinifera Cells | Plant-Microbe Interaction | Scoop.it
The high effectiveness of cyclic oligosaccharides like cyclodextrins in the production of trans-resveratrol in Vitis vinifera cell cultures is enhanced in the presence of methyl jasmonate. In order to dissect the basis of the interactions among the elicitation responses triggered by these two compounds, a transcriptional analysis of grapevine cell cultures treated with cyclodextrins and methyl jasmonate separately or in combination was carried out. The results showed that the activation of genes encoding enzymes from phenylpropanoid and stilbene biosynthesis induced by cyclodextrins alone was partially enhanced in the presence of methyl jasmonate, which correlated with their effects on trans-resveratrol production. In addition, protein translation and cell cycle regulation were more highly repressed in cells treated with cyclodextrins than in those treated with methyl jasmonate, and this response was enhanced in the combined treatment. Ethylene signalling was activated by all treatments, while jasmonate signalling and salicylic acid conjugation were activated only in the presence of methyl jasmonate and cyclodextrins, respectively. Moreover, the combined treatment resulted in a crosstalk between the signalling cascades activated by cyclodextrins and methyl jasmonate, which, in turn, provoked the activation of additional regulatory pathways involving the up-regulation of MYB15, NAC and WRKY transcription factors, protein kinases and calcium signal transducers. All these results suggest that both elicitors cause an activation of the secondary metabolism in detriment of basic cell processes like the primary metabolism or cell division. Crosstalk between cyclodextrins and methyl jasmonate-induced signalling provokes an intensification of these responses resulting in a greater trans-resveratrol production.

Via Christophe Jacquet
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Nutrient computation for root architecture

Nutrient computation for root architecture | Plant-Microbe Interaction | Scoop.it

Nitrogen is a major limiting nutrient for plants. Root systems acquire nitrogen through uptake of nutrients such as nitrate from the soil. Some plants can also obtain nitrogen by establishing a root nodule symbiosis with N-fixing bacteria. Whatever the means to acquire nutrients, an investment of the plant is required in which root architecture is suitably adapted. Therefore, plants integrate local and global nutrient cues to spend resources efficiently. On page 343 in this Science issue, Tabata et al. (1) identify a peptide signaling mechanism by which the root locally senses N limitation in the soil, and communicates with the shoot, which then signals back to the root to stimulate lateral root growth in regions with a high nitrate content to facilitate nitrate uptake.


Via Francis Martin
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Myosins VIII and XI Play Distinct Roles in Reproduction and Transport of Tobacco Mosaic Virus

Myosins VIII and XI Play Distinct Roles in Reproduction and Transport of Tobacco Mosaic Virus | Plant-Microbe Interaction | Scoop.it
Viruses are obligatory parasites that depend on host cellular factors for their replication as well as for their local and systemic movement to establish infection. Although myosin motors are thought to contribute to plant virus infection, their exact roles in the specific infection steps have not been addressed. Here we investigated the replication, cell-to-cell and systemic spread of Tobacco mosaic virus (TMV) using dominant negative inhibition of myosin activity. We found that interference with the functions of three class VIII myosins and two class XI myosins significantly reduced the local and long-distance transport of the virus. We further determined that the inactivation of myosins XI-2 and XI-K affected the structure and dynamic behavior of the ER leading to aggregation of the viral movement protein (MP) and to a delay in the MP accumulation in plasmodesmata (PD). The inactivation of myosin XI-2 but not of myosin XI-K affected the localization pattern of the 126k replicase subunit and the level of TMV accumulation. The inhibition of myosins VIII-1, VIII-2 and VIII-B abolished MP localization to PD and caused its retention at the plasma membrane. These results suggest that class XI myosins contribute to the viral propagation and intracellular trafficking, whereas myosins VIII are specifically required for the MP targeting to and virus movement through the PD. Thus, TMV appears to recruit distinct myosins for different steps in the cell-to-cell spread of the infection.

Via Suayib Üstün
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Experimental approaches to study plant cell walls during plant-microbe interactions

Plant cell walls provide physical strength, regulate the passage of bio-molecules, and act as the first barrier of defense against biotic and abiotic stress. In addition to providing structural integrity, plant cell walls serve an important function in connecting cells to their extracellular environment by sensing and transducing signals to activate cellular responses, such as those that occur during pathogen infection. This mini review will summarize current experimental approaches used to study cell wall functions during plant-pathogen interactions. Focus will be paid to cell imaging, spectroscopic analyses, and metabolic profiling techniques.


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Dss1 Is a 26S Proteasome Ubiquitin Receptor

Dss1 Is a 26S Proteasome Ubiquitin Receptor | Plant-Microbe Interaction | Scoop.it
Summary

The ubiquitin-proteasome system is the major pathway for protein degradation in eukaryotic cells. Proteins to be degraded are conjugated to ubiquitin chains that act as recognition signals for the 26S proteasome. The proteasome subunits Rpn10 and Rpn13 are known to bind ubiquitin, but genetic and biochemical data suggest the existence of at least one other substrate receptor. Here, we show that the phylogenetically conserved proteasome subunit Dss1 (Sem1) binds ubiquitin chains linked by K63 and K48. Atomic resolution data show that Dss1 is disordered and binds ubiquitin by binding sites characterized by acidic and hydrophobic residues. The complementary binding region in ubiquitin is composed of a hydrophobic patch formed by I13, I44, and L69 flanked by two basic regions. Mutations in the ubiquitin-binding site of Dss1 cause growth defects and accumulation of ubiquitylated proteins.

Via Christophe Jacquet, Suayib Üstün
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Frontiers | Methanol and ethanol modulate responses to danger- and microbe-associated molecular patterns | Plant-Microbe Interaction

Frontiers | Methanol and ethanol modulate responses to danger- and microbe-associated molecular patterns | Plant-Microbe Interaction | Plant-Microbe Interaction | Scoop.it
Methanol is a byproduct of cell wall modification, released through the action of pectin methylesterases (PMEs), which demethylesterify cell wall pectins. Plant PMEs play not only a role in developmental processes but also in responses to herbivory and infection by fungal or bacterial pathogens. Molecular mechanisms that explain how methanol affects plant defenses are poorly understood. Here we show that exogenously supplied methanol alone has weak effects on defense signaling in three dicot species, however, it profoundly alters signaling responses to danger- and microbe-associated molecular patterns (DAMPs, MAMPs) such as the alarm hormone systemin, the bacterial flagellum-derived flg22 peptide, and the fungal cell wall-derived oligosaccharide chitosan. In the presence of methanol the kinetics and amplitudes of DAMP/MAMP-induced MAP kinase (MAPK) activity and oxidative burst are altered in tobacco and tomato suspension-cultured cells, in Arabidopsis seedlings and tomato leaf tissue. As a possible consequence of altered DAMP/MAMP signaling, methanol suppressed the expression of the defense genes PR-1 and PI-1 in tomato. In cell cultures of the grass tall fescue (Festuca arundinacea, Poaceae, Monocots), methanol alone activates MAPKs and increases chitosan-induced MAPK activity, and in the darnel grass Lolium temulentum (Poaceae), it alters wound-induced MAPK signaling. We propose that methanol can be recognized by plants as a sign of the damaged self. In dicots, methanol functions as a DAMP-like alarm signal with little elicitor activity on its own, whereas it appears to function as an elicitor-active DAMP in monocot grasses. Ethanol had been implicated in plant stress responses, although the source of ethanol in plants is not well established. We found that it has a similar effect as methanol on responses to MAMPs and DAMPs.

Via Christophe Jacquet
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Rescooped by Guogen Yang from Virology and Bioinformatics from Virology.ca
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Ebola by the numbers: The size, spread and cost of an outbreak

Ebola by the numbers: The size, spread and cost of an outbreak | Plant-Microbe Interaction | Scoop.it
As the virus continues to rampage in West Africa, Nature’s graphic offers a guide to the figures that matter.

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Rescooped by Guogen Yang from Plant-Microbe Symbioses
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From soil to plant, the journey of P through trophic relationships and ectomycorrhizal association

From soil to plant, the journey of P through trophic relationships and ectomycorrhizal association | Plant-Microbe Interaction | Scoop.it
Phosphorus (P) is essential for plant growth and productivity. It is one of the most limiting macronutrients in soil because it is mainly present as unavailable, bound P whereas plants can only use unbound, inorganic phosphate (Pi), which is found in very low concentrations in soil solution. Some ectomycorrhizal fungi are able to release organic compounds (organic anions or phosphatases) to mobilize unavailable P. Recent studies suggest that bacteria play a major role in the mineralization of nutrients such as P through trophic relationships as they can produce specific phosphatases such as phytases to degrade phytate, the main form of soil organic P. Bacteria are also more effective than other microorganisms or plants at immobilizing free Pi. Therefore, bacterial grazing by grazers, such as nematodes, could release Pi locked in bacterial biomass. Free Pi may be taken up by ectomycorrhizal fungus by specific phosphate transporters and transferred to the plant by mechanisms that have not yet been identified. This mini-review aims to follow the phosphate pathway to understand the ecological and molecular mechanisms responsible for transfer of phosphate from the soil to the plant, to improve plant P nutrition.

Via Jean-Michel Ané
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Construction and comparison of gene co-expression networks shows complex plant immune responses

Construction and comparison of gene co-expression networks shows complex plant immune responses | Plant-Microbe Interaction | Scoop.it
Gene co-expression networks (GCNs) are graphic representations that depict the coordinated transcription of genes in response to certain stimuli. GCNs provide functional annotations of genes whose function is unknown and are further used in studies of translational functional genomics among species. In this work, a methodology for the reconstruction and comparison of GCNs is presented. This approach was applied using gene expression data that were obtained from immunity experiments in Arabidopsis thaliana, rice, soybean, tomato and cassava. After the evaluation of diverse similarity metrics for the GCN reconstruction, we recommended the mutual information coefficient measurement and a clustering coefficient-based method for similarity threshold selection. To compare GCNs, we proposed a multivariate approach based on the Principal Component Analysis (PCA). Branches of plant immunity that were exemplified by each experiment were analyzed in conjunction with the PCA results, suggesting both the robustness and the dynamic nature of the cellular responses. The dynamic of molecular plant responses produced networks with different characteristics that are differentiable using our methodology. The comparison of GCNs from plant pathosystems, showed that in response to similar pathogens plants could activate conserved signaling pathways. The results confirmed that the closeness of GCNs projected on the principal component space is an indicative of similarity among GCNs. This also can be used to understand global patterns of events triggered during plant immune responses.
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Elsa Ballini's curator insight, October 16, 3:13 AM

Some S-GCNs sharing similar stress groups were also identified in quadrant I of the PC1–PC2 plane (Fig. 4A). For example, networks 34 and 47, which are related to fungi experiments in Arabidopsis (ids 34; Botrytis cinerea) and rice (id 47;Magnaporthe oryzae). In the PC1–PC2 plane, they are forming a closer pair; therefore, their topological variables (clustering coefficient, density, heterogeneity and centralization) are analogous. Because of their position in PC2, we can conclude that they are disassortative and their linked genes do not share many functional annotations. Both networks are also close in the PC1–PC3 plane. Therefore, we can infer that the immunity processes that are represented in these networks (derived from plant–pathogen interactions of rice-Magnaporthe oryzae and Arabidopsis-Botrytis cinerea) could share some similarities.

Another example comprises the network 46. This network was obtained from rice plants that were inoculated with X. oryzae pv. oryzae, but also shows some degree of similarity with a network from Magnaporthe oryzae (id. 41). Some of the pathways can be shared in response to different pathogens at particular times during the infection or response. Consequently, the networks can exhibit this type of similarity.

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Plant Nutrition: Root Transporters on the Move

Plant Nutrition: Root Transporters on the Move | Plant-Microbe Interaction | Scoop.it

Nutrient and water uptake from the soil is essential for plant growth and development. In the root, absorption and radial transport of nutrients and water toward the vascular tissues is achieved by a battery of specialized transporters and channels. Modulating the amount and the localization of these membrane transport proteins appears as a way to drive their activity and is essential to maintain nutrient homeostasis in plants. This control first involves the delivery of newly synthesized proteins to the plasma membrane by establishing check points along the secretory pathway, especially during the export from the endoplasmic reticulum. Plasma membrane-localized transport proteins are internalized through endocytosis followed by recycling to the cell surface or targeting to the vacuole for degradation, hence constituting another layer of control. These intricate mechanisms are often regulated by nutrient availability, stresses, and endogenous cues, allowing plants to rapidly adjust to their environment and adapt their development.


Via Christophe Jacquet, Francis Martin
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