Plant immunity and legume symbiosis
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Plant immunity and legume symbiosis
Dedicated to plant mechanisms involved in response to pathogens, pests or symbionts. This site is complementary to the Plant pathogens and pests scoop-it site  :        http://www.scoop.it/t/erbilate. The role of hormones involved in regulation of plant responses to microorganisms is also reported in the "Plant hormones " site at http://www.scoop.it/t/plant-hormones-by-christophe-jacquet .
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Medicago truncatula ABCG10 is a transporter of 4-coumarate and liquiritigenin in the medicarpin biosynthetic pathway | Journal of Experimental Botany | Oxford Academic

Medicago truncatula  ABCG10 is a transporter of 4-coumarate and liquiritigenin in the medicarpin biosynthetic pathway | Journal of Experimental Botany | Oxford Academic | Plant immunity and legume symbiosis | Scoop.it
The ABCG10 protein of the model legume Medicago truncatula is required for efficient de novo production of the phenylpropanoid-derived phytoalexin medicarpin. Silencing the expression of MtABCG10 results, inter alia, in a lower accumulation of medicarpin and its precursors. In this study, we demonstrate that the impairment of medicarpin biosynthesis can be partially averted by the exogenous application of 4-coumarate, an early precursor of the core phenylpropanoid pathway, and the deoxyisoflavonoid formononetin. Experiments conducted using HPLC/MS in a heterologous system as well as in vitro transport assays with labelled substrate revealed that MtABCG10 is responsible for the membrane translocation of 4-coumarate and liquiritigenin, molecules representing key branching points in the phenylpropanoid pathway. The identification of transporters participating in the distribution of precursors is an important step in understanding phenylpropanoid biosynthesis.
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Intracellular Ca 2+ is important for flagellin-triggered defense in Arabidopsis and involves inositol polyphosphate signaling | Journal of Experimental Botany | Oxford Academic

Intracellular Ca 2+  is important for flagellin-triggered defense in Arabidopsis and involves inositol polyphosphate signaling | Journal of Experimental Botany | Oxford Academic | Plant immunity and legume symbiosis | Scoop.it
Cytosolic Ca2+ increase is a crucial and early step of plant immunity evoked by pathogen-associated molecular patterns (PAMPs) such as flagellin (flg). Components responsible for this increase are still not uncovered, although current models of plant immune signaling portray extracellular Ca2+ influx as paramount to flg activation of defense pathways. Work presented here provides new insights into cytosolic Ca2+ increase associated with flg-induced defense responses. We show that extracellular Ca2+ contributes more to immune responses evoked by plant elicitor peptide (Pep3) than that evoked by flg, indicating an intracellular Ca2+ source responsible for immune responses evoked by flg. Genetic impairment of the inositol polyphosphate (InsP) and G-protein signal associated with flg perception reduced flg-dependent immune responses. Previous work indicates that prior exposure of Arabidopsis plants to flg leads to an immune response reflected by less vigorous growth of a pathogenic microbe. We found that this immune response to flg was compromised in mutants lacking the ability to generate an InsP or G-protein signal. We conclude that the recruitment of intracellular Ca2+ stores by flg may involve InsP and G-protein signaling. We also found a notable difference in contribution of intracellular stores of Ca2+ to the immune signaling evoked by another PAMP, elf18 peptide, which had a very different response profile to impairment of InsP signaling. Although Ca2+ signaling is at the core of the innate immune as well as hypersensitive response to plant pathogens, it appears that the molecular mechanisms generating the Ca2+ signal in response to different PAMPs are different.
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Scientific Reports - PRR2, a pseudo-response regulator, promotes salicylic acid and camalexin accumulation during plant immunity

Scientific Reports - PRR2, a pseudo-response regulator, promotes salicylic acid and camalexin accumulation during plant immunity | Plant immunity and legume symbiosis | Scoop.it

Calcium signalling mediated by Calmodulin (CaM) and calmodulin-like (CML) proteins is critical to plant immunity. CaM and CML regulate a wide range of target proteins and cellular responses. While many CaM-binding proteins have been identified, few have been characterized for their specific role in plant immunity. Here, we report new data on the biological function of a CML-interacting partner, PRR2 (PSEUDO-RESPONSE REGULATOR 2), a plant specific transcription factor. Until now, the physiological relevance of PRR2 remained largely unknown. Using a reverse genetic strategy in A. thaliana, we identified PRR2 as a positive regulator of plant immunity. We propose that PRR2 contributes to salicylic acid (SA)-dependent responses when challenged with the phytopathogenic bacterium Pseudomonas syringae. PRR2 is transcriptionally upregulated by SA and P. syringae, enhances SA biosynthesis and SA signalling responses; e.g. in response to P. syringae, PRR2 induces the production of SA and the accumulation of the defence-related protein PR1. Moreover, PRR2 overexpressing lines exhibit an enhanced production of camalexin, a phytoalexin that confers enhanced resistance against pathogens. Together, these data reveal the importance of PRR2 in plant immune responses against P. syringae and suggest a novel function for this particular plant specific transcription factor in plant physiology.


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Simultaneous modification of three homoeologs of TaEDR1 by genome editing enhances powdery mildew resistance in wheat

Simultaneous modification of three homoeologs of TaEDR1 by genome editing enhances powdery mildew resistance in wheat | Plant immunity and legume symbiosis | Scoop.it
Wheat (Triticum aestivum L.) incurs significant yield losses from powdery mildew, a major fungal disease caused by Blumeria graminis f. sp. tritici (Bgt). enhanced disease resistance1 (EDR1) plays a negative role in the defense response against powdery mildew in Arabidopsis thaliana; however, the edr1 mutant does not show constitutively activated defense responses. This makes EDR1 an ideal target for approaches using new genome-editing tools to improve resistance to powdery mildew. We cloned TaEDR1 from hexaploid wheat and found high similarity among the three homoeologs of EDR1. Knock-down of TaEDR1 by virus-induced gene silencing or RNA interference enhanced resistance to powdery mildew, indicating that TaEDR1 negatively regulates powdery mildew resistance in wheat. We used CRISPR/Cas9 technology to generate Taedr1 wheat plants by simultaneous modification of the three homoeologs of wheat EDR1. No off-target mutations were detected in the Taedr1 mutant plants. The Taedr1 plants were resistant to powdery mildew and did not show mildew-induced cell death. Our study represents the successful generation of a potentially valuable trait using genome-editing technology in wheat and provides germplasm for disease resistance breeding.
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Legume LysM receptors mediate symbiotic and pathogenic signalling - ScienceDirect

Legume LysM receptors mediate symbiotic and pathogenic signalling - ScienceDirect | Plant immunity and legume symbiosis | Scoop.it

Highlights

• LysM receptor kinases differentiate symbiotic and pathogenic microbial signals.
• LysM receptor kinases perceive a wider range of ligands than previously anticipated.
• Receptor complex formation and signalling are modulated by interacting proteins.

Legume–rhizobia symbiosis is coordinated through the production and perception of signal molecules by both partners with legume LysM receptor kinases performing a central role in this process. Receptor complex formation and signalling outputs derived from these are regulated through ligand binding and further modulated by a diverse variety of interactors. The challenge now is to understand the molecular mechanisms of these reported interactors. Recently attributed roles of LysM receptors in the perception of rhizobial exopolysaccharide, distinguishing between pathogens and symbionts, and assembly of root and rhizosphere communities expand on the importance of these receptors. These studies also highlight challenges, such as identification of cognate ligands, formation of responsive receptor complexes and separation of downstream signal transduction pathways.

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E3 ligase SAUL1 serves as a positive regulator of PAMP‐triggered immunity and its homeostasis is monitored by immune receptor SOC3

E3 ligase SAUL1 serves as a positive regulator of PAMP‐triggered immunity and its homeostasis is monitored by immune receptor SOC3 | Plant immunity and legume symbiosis | Scoop.it
In both plants and animals, intracellular nucleotide-binding leucine-rich repeat proteins (NLRs; or Nod-like receptors) serve as immune receptors to recognize pathogen-derived molecules and mount effective immune responses against microbial infections. Plant NLRs often guard the presence or activity of other host proteins, which are the direct virulence targets of pathogen effectors. These guardees are sometimes immune-promoting components such as those in a mitogen-activated protein kinase cascade. Plant E3 ligases serve many roles in immune regulation, but it is unclear whether they can also be guarded by NLRs.
Here, we report on an immune-regulating E3 ligase SAUL1, whose homeostasis is monitored by a Toll interleukin 1 receptor (TIR)-type NLR (TNL), SOC3.
SOC3 can associate with SAUL1, and either loss or overexpression of SAUL1 triggers autoimmunity mediated by SOC3. By contrast, SAUL1 functions redundantly with its close homolog PUB43 to promote PAMP-triggered immunity (PTI).
Taken together, the E3 ligase SAUL1 serves as a positive regulator of PTI and its homeostasis is monitored by the TNL SOC3.
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A plant's balance of growth and defense – revisited

A plant's balance of growth and defense – revisited | Plant immunity and legume symbiosis | Scoop.it
The sessile lifestyle of plants requires a permanent and efficient adjustment to environmental stresses caused by biotic factors, such as pathogens and herbivores, or abiotic factors, such as drought and salt. Any defense responses, however, are costly, and investment into defense leads to reduced growth. These plant growth–defense tradeoffs, with simultaneous activation of defense and maintenance of growth, are critical for crop breeding. For some stresses, such as wounding by herbivores, the cost–benefit ratio in the growth–defense tradeoff has been tested in native populations; a costly jasmonic acid (JA)-induced defense response has been shown, which is down-regulated when the defense is not required (Baldwin, 1998). JA is the central player in many stress responses: inhibition of root growth, photosynthesis, and leaf growth (Zhang & Turner, 2008), induction of defense proteins, formation of secondary compounds active in defense and defense upon bacterial infection are JA-induced processes with consequences for growth
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Expansion of sesquiterpene biosynthetic gene clusters in pepper confers nonhost resistance to the Irish potato famine pathogen

Expansion of sesquiterpene biosynthetic gene clusters in pepper confers nonhost resistance to the Irish potato famine pathogen | Plant immunity and legume symbiosis | Scoop.it
Chemical barriers contribute to nonhost resistance, which is defined as the resistance of an entire plant species to nonadapted pathogen species. However, the molecular basis of metabolic defense in nonhost resistance remains elusive.
Here, we report genetic evidence for the essential role of phytoalexin capsidiol in nonhost resistance of pepper (Capsicum spp.) to potato late blight Phytophthora infestans using transcriptome and genome analyses.
Two different genes for capsidiol biosynthesis, 5-epi-aristolochene synthase (EAS) and 5-epi-aristolochene-1,3-dihydroxylase (EAH), belong to multigene families. However, only a subset of EAS/EAH gene family members were highly induced upon P. infestans infection, which was associated with parallel accumulation of capsidiol in P. infestans-infected pepper. Silencing of EAS homologs in pepper resulted in a significant decrease in capsidiol accumulation and allowed the growth of nonadapted P. infestans that is highly sensitive to capsidiol. Phylogenetic and genomic analyses of EAS/EAH multigene families revealed that the emergence of pathogen-inducible EAS/EAH genes in Capsicum-specific genomic regions rendered pepper a nonhost of P. infestans.
This study provides insights into evolutionary aspects of nonhost resistance based on the combination of a species-specific phytoalexin and sensitivity of nonadapted pathogens.
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Interplay Between Innate Immunity and the Plant Microbiota | Annual Review of Phytopathology

Interplay Between Innate Immunity and the Plant Microbiota | Annual Review of Phytopathology | Plant immunity and legume symbiosis | Scoop.it
The innate immune system of plants recognizes microbial pathogens and terminates their growth. However, recent findings suggest that at least one layer of this system is also engaged in cooperative plant-microbe interactions and influences host colonization by beneficial microbial communities. This immune layer involves sensing of microbe-associated molecular patterns (MAMPs) by pattern recognition receptors (PRRs) that initiate quantitative immune responses to control host-microbial load, whereas diversification of MAMPs and PRRs emerges as a mechanism that locally sculpts microbial assemblages in plant populations. This suggests a more complex microbial management role of the innate immune system for controlled accommodation of beneficial microbes and in pathogen elimination. The finding that similar molecular strategies are deployed by symbionts and pathogens to dampen immune responses is consistent with this hypothesis but implies different selective pressures on the immune system due to contrasting outcomes on plant fitness. The reciprocal interplay between microbiota and the immune system likely plays a critical role in shaping beneficial plant-microbiota combinations and maintaining microbial homeostasis.
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What Do We Know About NOD-Like Receptors in Plant Immunity? | Annual Review of Phytopathology

What Do We Know About NOD-Like Receptors in Plant Immunity? | Annual Review of Phytopathology | Plant immunity and legume symbiosis | Scoop.it
The first plant disease resistance (R) genes were identified and cloned more than two decades ago. Since then, many more R genes have been identified and characterized in numerous plant pathosystems. Most of these encode members of the large family of intracellular NLRs (NOD-like receptors), which also includes animal immune receptors. New discoveries in this expanding field of research provide new elements for our understanding of plant NLR function. But what do we know about plant NLR function today? Genetic, structural, and functional analyses have uncovered a number of commonalities and differences in pathogen recognition strategies as well as how NLRs are regulated and activate defense signaling, but many unknowns remain. This review gives an update on the latest discoveries and breakthroughs in this field, with an emphasis on structural findings and some comparison to animal NLRs, which can provide additional insights and paradigms in plant NLR function.
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Transfer and engineering of immune receptors to improve recognition capacities in crops - ScienceDirect

Transfer and engineering of immune receptors to improve recognition capacities in crops - ScienceDirect | Plant immunity and legume symbiosis | Scoop.it

Highlights

• Extracellular and intracellular receptors sense pathogen invasion to activate defence.
• Understanding of immune receptor functioning permits interfamily exploitation.
• Recombination of immune receptors may lead to novel recognition specificities.
• Engineering of effector targets may extend immune receptor recognition spectrum.
• Novel tools and strategies foster exploitation of immune receptors in crops.

Immune receptors are pivotal elements of the plant immune system that act as sentinels for microbial invasion. Knowingly or unknowingly, breeding for resistance has largely relied on the transfer of immune receptor recognition specificities between plant genotypes. For decades such transfers were limited to crossable species. However, advents in transgene technologies have allowed overcoming species barriers. Novel strategies for mining of recognition specificities, combined with our recently increased understanding of immune receptor functioning, allows to increase and alter recognition specificities, which should ultimately increase the spectrum of recognition specificities that are available to control plant diseases in crops.

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A gene encoding maize caffeoyl-CoA O-methyltransferase confers quantitative resistance to multiple pathogens 

A gene encoding maize caffeoyl-CoA O-methyltransferase confers quantitative resistance to multiple pathogens  | Plant immunity and legume symbiosis | Scoop.it
Alleles that confer multiple disease resistance (MDR) are valuable in crop improvement, although the molecular mechanisms underlying their functions remain largely unknown. A quantitative trait locus, qMdr9.02, associated with resistance to three important foliar maize diseases—southern leaf blight, gray leaf spot and northern leaf blight—has been identified on maize chromosome 9. Through fine-mapping, association analysis, expression analysis, insertional mutagenesis and transgenic validation, we demonstrate that ZmCCoAOMT2, which encodes a caffeoyl-CoA O-methyltransferase associated with the phenylpropanoid pathway and lignin production, is the gene within qMdr9.02 conferring quantitative resistance to both southern leaf blight and gray leaf spot. We suggest that resistance might be caused by allelic variation at the level of both gene expression and amino acid sequence, thus resulting in differences in levels of lignin and other metabolites of the phenylpropanoid pathway and regulation of programmed cell death.
 

Via Yogesh Gupta, Jennifer Mach, CP
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Frontiers | A Novel Soybean Dirigent Gene GmDIR22 Contributes to Promotion of Lignan Biosynthesis and Enhances Resistance to Phytophthora sojae | Plant Science

Frontiers | A Novel Soybean Dirigent Gene GmDIR22 Contributes to Promotion of Lignan Biosynthesis and Enhances Resistance to Phytophthora sojae | Plant Science | Plant immunity and legume symbiosis | Scoop.it
Phytophthora root and stem rot caused by the oomycete pathogen Phytophthora sojae is a destructive disease of soybean worldwide. Plant dirigent proteins (DIR) are proposed to have roles in biosynthesis of either lignan or lignin-like molecules, and are important for defense responses, secondary metabolism, and pathogen resistance. In the present work, a novel DIR gene expressed sequence tag is identified as up-regulated in the highly resistant soybean cultivar ‘Suinong 10’ inoculated with P. sojae. The full length cDNA is isolated using rapid amplification of cDNA ends, and designated GmDIR22 (GenBank accession no. HQ_993047). The full length GmDIR22 is 789 bp and contains a 567 bp open reading frame encoding a polypeptide of 188 amino acids. The sequence analysis indicated that GmDIR22 contains a conserved dirigent domain at amino acid residues 43–187. The quantitative real-time reverse transcription PCR demonstrated that soybean GmDIR22 mRNA is expressed most highly in stems, followed by roots and leaves. The treatments with stresses demonstrated that GmDIR22 is significantly induced by P. sojae and gibberellic acid (GA3), and also responds to salicylic acid, methyl jasmonic acid, and abscisic acid. The GmDIR22 is targeted to the cytomembrane when transiently expressed in Arabidopsis protoplasts. Moreover, The GmDIR22 recombinant protein purified from Escherichia coli could effectively direct E-coniferyl alcohol coupling into lignan (+)-pinoresinol. Accordingly, the overexpression of GmDIR22 in transgenic soybean increased total lignan accumulation. Moreover, the lignan extracts from GmDIR22 transgenic plants effectively inhibits P. sojae hyphal growth. Furthermore, the transgenic overexpression of GmDIR22 in the susceptible soybean cultivar ‘Dongnong 50’ enhances its resistance to P. sojae. Collectively, these data suggested that the primary role of GmDIR22 is probably involved in the regulation of lignan biosynthesis, and which contributes to resistance to P. sojae.
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RIN4 recruits the exocyst subunit EXO70B1 to the plasma membrane | Journal of Experimental Botany | Oxford Academic

RIN4 recruits the exocyst subunit EXO70B1 to the plasma membrane | Journal of Experimental Botany | Oxford Academic | Plant immunity and legume symbiosis | Scoop.it
The exocyst is a conserved vesicle-tethering complex with principal roles in cell polarity and morphogenesis. Several studies point to its involvement in polarized secretion during microbial pathogen defense. In this context, we have found an interaction between the Arabidopsis EXO70B1 exocyst subunit, a protein which was previously associated with both the defense response and autophagy, and RPM1 INTERACTING PROTEIN 4 (RIN4), the best studied member of the NOI protein family and a known regulator of plant defense pathways. Interestingly, fragments of RIN4 mimicking the cleavage caused by the Pseudomonas syringae effector protease, AvrRpt2, fail to interact strongly with EXO70B1. We observed that transiently expressed RIN4, but not the plasma membrane (PM) protein aquaporin PIP2, recruits EXO70B1 to the PM. Unlike EXO70B1, RIN4 does not recruit the core exocyst subunit SEC6 to the PM under these conditions. Furthermore, the AvrRpt2 effector protease delivered by P. syringae is able to release both RIN4 and EXO70B1 to the cytoplasm. We present a model for how RIN4 might regulate the localization and putative function of EXO70B1 and speculate on the role the AvrRpt2 protease might have in the regulation of this defense response.
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CBL-interacting protein kinase 6 negatively regulates immune response to Pseudomonas syringae in Arabidopsis | Journal of Experimental Botany | Oxford Academic

CBL-interacting protein kinase 6 negatively regulates immune response to  Pseudomonas syringae  in Arabidopsis | Journal of Experimental Botany | Oxford Academic | Plant immunity and legume symbiosis | Scoop.it
Cytosolic calcium ion (Ca2+) is an essential mediator of the plant innate immune response. Here, we report that a calcium-regulated protein kinase Calcineurin B-like protein (CBL)-interacting protein kinase 6 (CIPK6) functions as a negative regulator of immunity against the bacterial pathogen Pseudomonas syringae in Arabidopsis thaliana. Arabidopsis lines with compromised expression of CIPK6 exhibited enhanced disease resistance to the bacterial pathogen and to P. syringae harboring certain but not all avirulent effectors, while restoration of CIPK6 expression resulted in abolition of resistance. Plants overexpressing CIPK6 were more susceptible to P. syringae. Enhanced resistance in the absence of CIPK6 was accompanied by increased accumulation of salicylic acid and elevated expression of defense marker genes. Salicylic acid accumulation was essential for improved immunity in the absence of CIPK6. CIPK6 negatively regulated the oxidative burst associated with perception of pathogen-associated microbial patterns (PAMPs) and bacterial effectors. Accelerated and enhanced activation of the mitogen-activated protein kinase cascade in response to bacterial and fungal elicitors was observed in the absence of CIPK6. The results of this study suggested that CIPK6 negatively regulates effector-triggered and PAMP-triggered immunity in Arabidopsis.
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GBF1 differentially regulates CAT2 and PAD4 transcription to promote pathogen defense in Arabidopsis thaliana

GBF1 differentially regulates CAT2 and PAD4 transcription to promote pathogen defense in Arabidopsis thaliana | Plant immunity and legume symbiosis | Scoop.it
G-BOX BINDING FACTOR 1 (GBF1) influences light-regulated seedling development in Arabidopsis, and inhibits CATALASE 2 (CAT2) expression during senescence. CAT2 functions as a scavenger of hydrogen peroxide. The role of GBF1 in the defense response is not known. We report here that GBF1 positively influences the defense against virulent and avirulent strains of Pseudomonas syringae. The gbf1 mutants are susceptible, whereas GBF1 over-expresser transgenic plants are resistant to bacterial pathogens. GBF1 negatively regulates pathogen-induced CAT2 expression and thereby positively regulates the hypersensitive response. In addition to CAT2 promoter, GBF1 binds to the G-box-like element present in the intron of PHYTOALEXIN DEFICIENT 4 (PAD4). This association of GBF1 with PAD4 intron is enhanced upon pathogenesis. GBF1 positively regulates PAD4 transcription in an intron-dependent manner. GBF1-mediated positive regulation of PAD4 expression is also evident in gbf1 mutant and GBF1 over-expression lines. Similar to pad4 mutants, pathogen-induced camalexin and salicylic acid (SA) accumulation, and expression of SA-inducible PATHOGENESIS RELATED1 (PR1) gene are compromised in the gbf1 mutant. Exogenous application of SA rescues the loss-of-defense phenotypes of gbf1 mutant. Thus, altogether, our results demonstrate that GBF1 is an important component of the plant defense response that functions upstream of SA accumulation and, by oppositely regulating CAT2 and PAD4, promotes disease resistance in Arabidopsis.
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Membrane Trafficking in Plant Immunity - ScienceDirect

Membrane Trafficking in Plant Immunity - ScienceDirect | Plant immunity and legume symbiosis | Scoop.it
Plants employ sophisticated mechanisms to interact with pathogenic as well as beneficial microbes. Of those, membrane trafficking is key in establishing a rapid and precise response. Upon interaction with pathogenic microbes, surface-localized immune receptors undergo endocytosis for signal transduction and activity regulation while cell wall components, antimicrobial compounds, and defense proteins are delivered to pathogen invasion sites through polarized secretion. To sustain mutualistic associations, host cells also reprogram the membrane trafficking system to accommodate invasive structures of symbiotic microbes. Here, we provide an analysis of recent advances in understanding the roles of secretory and endocytic membrane trafficking pathways in plant immune activation. We also discuss strategies deployed by adapted microbes to manipulate these pathways to subvert or inhibit plant defense.
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Fats and function: protein lipid modifications in plant cell signalling - ScienceDirect

Fats and function: protein lipid modifications in plant cell signalling - ScienceDirect | Plant immunity and legume symbiosis | Scoop.it

Highlights

• Many plant proteins can be N-myristoylated, prenylated, or S-acylated.
• Lipid modifications provide more than just a membrane anchor.
•Proteomics advances reveal hundreds of proteins to be lipid-modified in plants.
• Signalling proteins are enriched in the lipid-modified plant proteome.
• Dynamic S-acylation can regulate protein function.

The post-translational lipid modifications N-myristoylation, prenylation and S-acylation are traditionally associated with increasing protein membrane affinity and localisation. However this is an over-simplification, with evidence now implicating these modifications in a variety of roles such as membrane microdomain partitioning, protein trafficking, protein complex assembly and polarity maintenance. Evidence for a regulatory role is also emerging, with changes or manipulation of lipid modifications offering a means of directly controlling various aspects of protein function. Proteomics advances have revealed an enrichment of signalling proteins in the lipid-modified proteome, potentially indicating an important role for these modifications in responding to stimuli. This review highlights some of the key themes and possible functions of lipid modification during signalling processes in plants.

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A transposon‐directed epigenetic change in ZmCCT underlies quantitative resistance to Gibberella stalk rot in maize

A transposon‐directed epigenetic change in ZmCCT underlies quantitative resistance to Gibberella stalk rot in maize | Plant immunity and legume symbiosis | Scoop.it
A major resistance quantitative trait locus, qRfg1, significantly enhances maize resistance to Gibberella stalk rot, a devastating disease caused by Fusarium graminearum. However, the underlying molecular mechanism remains unknown.
We adopted a map-based cloning approach to identify the resistance gene at qRfg1 and examined the dynamic epigenetic changes during qRfg1-mediated maize resistance to the disease.
A CCT domain-containing gene, ZmCCT, is the causal gene at the qRfg1 locus and a polymorphic CACTA-like transposable element (TE1) c. 2.4 kb upstream of ZmCCT is the genetic determinant of allelic variation. The non-TE1 ZmCCT allele is in a poised state, with predictive bivalent chromatin enriched for both repressive (H3K27me3/H3K9me3) and active (H3K4me3) histone marks. Upon pathogen challenge, this non-TE1 ZmCCT allele was promptly induced by a rapid yet transient reduction in H3K27me3/H3K9me3 and a progressive decrease in H3K4me3, leading to disease resistance. However, TE1 insertion in ZmCCT caused selective depletion of H3K4me3 and enrichment of methylated GC to suppress the pathogen-induced ZmCCT expression, resulting in disease susceptibility. Moreover, ZmCCT-mediated resistance to Gibberella stalk rot is not affected by photoperiod sensitivity.
This chromatin-based regulatory mechanism enables ZmCCT to be more precise and timely in defense against F. graminearum infection.
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Silencing of AtRAP, a target gene of a bacteria‐induced small RNA, triggers antibacterial defense responses through activation of LSU2 and down‐regulation of GLK1

Silencing of AtRAP, a target gene of a bacteria‐induced small RNA, triggers antibacterial defense responses through activation of LSU2 and down‐regulation of GLK1 | Plant immunity and legume symbiosis | Scoop.it
Plants fine-tune their sophisticated immunity systems in response to pathogen infections. We previously showed that AtlsiRNA-1, a bacteria-induced plant endogenous small interfering RNA, silences the AtRAP gene, which encodes a putative RNA binding protein.
In this study, we demonstrate that AtRAP functions as a negative regulator in plant immunity by characterizing molecular and biological responses of the knockout mutant and overexpression lines of AtRAP upon bacterial infection.
AtRAP is localized in chloroplasts and physically interacts with Low Sulfur Upregulated 2 (LSU2), which positively regulates plant defense. Our results suggest that AtRAP negatively regulates defense responses by suppressing LSU2 through physical interaction. We also detected downregulation of the transcription factor GOLDEN2-LIKE 1 (GLK1) in atrap-1 using microarray analysis. The glk1 glk2 double mutant showed enhanced resistance to Pseudomonas syringae pv. tomato, which is consistent with a previous study showing enhanced resistance of a glk1 glk2 double mutant to Hyaloperonospora arabidopsidis.
Taken together, our data suggest that silencing of AtRAP by AtlsiRNA-1 upon bacterial infection triggers defense responses through regulation of LSU2 and GLK1.
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From Chaos to Harmony: Responses and Signaling upon Microbial Pattern Recognition | Annual Review of Phytopathology

From Chaos to Harmony: Responses and Signaling upon Microbial Pattern Recognition | Annual Review of Phytopathology | Plant immunity and legume symbiosis | Scoop.it
Pathogen- or microbe-associated molecular patterns (PAMPs/MAMPs) are detected as nonself by host pattern recognition receptors (PRRs) and activate pattern-triggered immunity (PTI). Microbial invasions often trigger the production of host-derived endogenous signals referred to as danger- or damage-associated molecular patterns (DAMPs), which are also perceived by PRRs to modulate PTI responses. Collectively, PTI contributes to host defense against infections by a broad range of pathogens. Remarkable progress has been made toward demonstrating the cellular and physiological responses upon pattern recognition, elucidating the molecular, biochemical, and genetic mechanisms of PRR activation, and dissecting the complex signaling networks that orchestrate PTI responses. In this review, we present an update on the current understanding of how plants recognize and respond to nonself patterns, a process from which the seemingly chaotic responses form into a harmonic defense.
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Fatty Acid– and Lipid-Mediated Signaling in Plant Defense | Annual Review of Phytopathology

Fatty Acid– and Lipid-Mediated Signaling in Plant Defense | Annual Review of Phytopathology | Plant immunity and legume symbiosis | Scoop.it
Fatty acids and lipids, which are major and essential constituents of all plant cells, not only provide structural integrity and energy for various metabolic processes but can also function as signal transduction mediators. Lipids and fatty acids can act as both intracellular and extracellular signals. In addition, cyclic and acyclic products generated during fatty acid metabolism can also function as important chemical signals. This review summarizes the biosynthesis of fatty acids and lipids and their involvement in pathogen defense.
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Pathogen recognition in compatible plant-microbe interactions

Pathogen recognition in compatible plant-microbe interactions | Plant immunity and legume symbiosis | Scoop.it
Microbial infections in plant leaves remain a major challenge in agriculture. Hence an understanding of disease mechanisms at the molecular level is of paramount importance for identifying possible intervention points for their control. Whole-transcriptome changes during early disease stages in susceptible plant species are less well-documented than those of resistant ones. This study focuses on the differential transcriptional changes at 24 hours post inoculation (hpi) in tomato leaflets affected by three pathogens: (1) Phytophthora infestans, (2) Botrytis cinerea, and (3) Oidium neolycopersici. Grey mould (B. cinerea) was the disease that had progressed the most by 24 hpi, both in terms of visible symptoms as well as differential gene expression. By means of RNA-seq, we identified 50 differentially expressed tomato genes specifically induced by B. cinerea infection and 18 specifically induced by P. infestans infection at 24 hpi. Additionally, a set of 63 genes were differentially expressed during all three diseases when compared by a Bayesian approach to their respective mock infections. And Gene expression patterns were found to also depend on the inoculation technique. These findings suggest a specific and distinct transcriptional response in plant leaf tissue in reaction to B. cinerea and P. infestans invasion at 24 hpi, indicating that plants may recognize the attacking pathogen.
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Cytokinins in Symbiotic Nodulation: When, Where, What For?

Cytokinins in Symbiotic Nodulation: When, Where, What For? | Plant immunity and legume symbiosis | Scoop.it

Substantial progress has been made in the understanding of early stages of the symbiotic interaction between legume plants and rhizobium bacteria. Those include the specific recognition of symbiotic partners, the initiation of bacterial infection in root hair cells, and the inception of a specific organ in the root cortex, the nodule. Increasingly complex regulatory networks have been uncovered in which cytokinin (CK) phytohormones play essential roles in different aspects of early symbiotic stages. Intriguingly, these roles can be either positive or negative, cell autonomous or non-cell autonomous, and vary, depending on time, root tissues, and possibly legume species. Recent developments on CK symbiotic functions and interconnections with other signaling pathways during nodule initiation are the focus of this review.

Trends

In addition to the well-documented positive role of CK phytohormones in nitrogen-fixing nodule inception, additional functions linked to other aspects of this symbiotic interaction have emerged.

Negative CK functions in the root epidermis have been identified in relation with rhizobial infections and the NF signaling pathway mediating bacterial symbiont recognition and infection.

Potential non-cell autonomous functions of CK occur at short distance between root epidermal and cortical layers and at long distance between shoots and roots in the frame of the ‘autoregulation of nodulation’ systemic pathway.

Identifying specificities of CK pathways in the different root tissues involved in nodulation and their crosstalk with other hormonal pathways remains a challenge required for a detailed mechanistic understanding of the initial stages of symbiotic nodulation.

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Darryn Whisgary's curator insight, July 28, 8:12 AM
"Complex regulatory networks have been uncovered in which cytokinin (CK) phytohormones play essential roles in different aspects of early symbiotic stages"
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Frontiers | A Proteomic View on the Role of Legume Symbiotic Interactions | Plant Science

Frontiers | A Proteomic View on the Role of Legume Symbiotic Interactions | Plant Science | Plant immunity and legume symbiosis | Scoop.it
Legume plants are key elements in sustainable agriculture and represent a significant source of plant-based protein for humans and animal feed worldwide. One specific feature of the family is the ability to establish nitrogen-fixing symbiosis with Rhizobium bacteria. Additionally, like most vascular flowering plants, legumes are able to form a mutualistic endosymbiosis with arbuscular mycorrhizal (AM) fungi. These beneficial associations can enhance the plant resistance to biotic and abiotic stresses. Understanding how symbiotic interactions influence and increase plant stress tolerance are relevant questions toward maintaining crop yield and food safety in the scope of climate change. Proteomics offers numerous tools for the identification of proteins involved in such responses, allowing the study of sub-cellular localization and turnover regulation, as well as the discovery of post-translational modifications (PTMs). The current work reviews the progress made during the last decades in the field of proteomics applied to the study of the legume-Rhizobium and -AM symbioses, and highlights their influence on the plant responses to pathogens and abiotic stresses. We further discuss future perspectives and new experimental approaches that are likely to have a significant impact on the field including peptidomics, mass spectrometric imaging, and quantitative proteomics.
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