Role In Plant-pathogen Interactions Research Articles

Pseudomonas syringae pv. actinidiae Effector HopAU1 Interacts with Calcium-Sensing Receptor to Activate Plant Immunity.

Kiwifruit canker, caused by Pseudomonas syringae pv. actinidiae (Psa), is a destructive pathogen that globally threatens the kiwifruit industry. Understanding the molecular mechanism of plant-pathogen interaction can accelerate applying resistance breeding and controlling plant diseases. All known effectors secreted by pathogens play an important role in plant-pathogen interaction. However, the effectors in Psa and their function mechanism remain largely unclear. Here, we successfully identified a T3SS effector HopAU1 which had no virulence contribution to Psa, but could, however, induce cell death and activate a series of immune responses by agroinfiltration in Nicotiana benthamiana, including elevated transcripts of immune-related genes, accumulation of reactive oxygen species (ROS), and callose deposition. We found that HopAU1 interacted with a calcium sensing receptor in N. benthamiana (NbCaS) as well as its close homologue in kiwifruit (AcCaS). More importantly, silencing CaS by RNAi in N. benthamiana greatly attenuated HopAU1-triggered cell death, suggesting CaS is a crucial component for HopAU1 detection. Further researches showed that overexpression of NbCaS in N. benthamiana significantly enhanced plant resistance against Sclerotinia sclerotiorum and Phytophthora capsici, indicating that CaS serves as a promising resistance-related gene for disease resistance breeding. We concluded that HopAU1 is an immune elicitor that targets CaS to trigger plant immunity.

Fungal oxysterol-binding protein-related proteins promote pathogen virulence and activate plant immunity.

Oxysterol-binding protein-related proteins (ORPs) are a conserved class of lipid transfer proteins that are closely involved in multiple cellular processes in eukaryotes, but their roles in plant-pathogen interactions are mostly unknown. We show that transient expression of ORPs of Magnaporthe oryzae (MoORPs) in Nicotiana benthamina plants triggered oxidative bursts and cell death; treatment of tobacco Bright Yellow-2 suspension cells with recombinant MoORPs elicited the production of reactive oxygen species. Despite ORPs being normally described as intracellular proteins, we detected MoORPs in fungal culture filtrates and intercellular fluids from barley plants infected with the fungus. More importantly, infiltration of Arabidopsis plants with recombinant Arabidopsis or fungal ORPs activated oxidative bursts, callose deposition, and PR1 gene expression, and enhanced plant disease resistance, implying that ORPs may function as endogenous and exogenous danger signals triggering plant innate immunity. Extracellular application of fungal ORPs exerted an opposite impact on salicylic acid and jasmonic acid/ethylene signaling pathways. Brassinosteroid Insensitive 1-associated Kinase 1 was dispensable for the ORP-activated defense. Besides, simultaneous knockout of MoORP1 and MoORP3 abolished fungal colony radial growth and conidiation, whereas double knockout of MoORP1 and MoORP2 compromised fungal virulence on barley and rice plants. These observations collectively highlight the multifaceted role of MoORPs in the modulation of plant innate immunity and promotion of fungal development and virulence in M. oryzae.

The Role of Plant Hormones in the Interaction of Colletotrichum Species with Their Host Plants.

Colletotrichum is a plant pathogenic fungus which is able to infect virtually every economically important plant species. Up to now no common infection mechanism has been identified comparing different plant and Colletotrichum species. Plant hormones play a crucial role in plant-pathogen interactions regardless whether they are symbiotic or pathogenic. In this review we analyze the role of ethylene, abscisic acid, jasmonic acid, auxin and salicylic acid during Colletotrichum infections. Different Colletotrichum strains are capable of auxin production and this might contribute to virulence. In this review the role of different plant hormones in plant—Colletotrichum interactions will be discussed and thereby auxin biosynthetic pathways in Colletotrichum spp. will be proposed.

Genome-wide Characterization Deciphers Distinct Properties of Aquaporins in Six Phytophthora Species

Background: Aquaporins, also known as major intrinsic proteins (MIPs), facilitate the membrane diffusion of water and some other small solutes. The roles of MIPs in plant physiological processes are established and now their roles in plant-pathogen interactions are getting more attention. Objective: To investigate the evolution, diversity, and structural insights of Phytophthora MIPs (PhyMIPs) and to compare them to those in other domains of life. Methods: Bioinformatics approaches were used to identify and characterize the PhyMIPs. The phylogenetic analysis was done with MEGA7.0 using maximum likelihood method. The prediction of transmembrane α-helices was done by using SOSUI and TMpred servers, and that of subcellular localization was performed with WoLF PSORT and Cello prediction system. The structure of PhyMIP genes was predicted by GeneMark.hmm ES-3.0 program. The 3D homology models were generated using the Molecular Operating Environment software and the stereochemical quality of the templates and models was assessed by PROCHECK. The PoreWalker server was used to detect and characterize PhyMIP channels from their 3D structural models. Results: Herein, we identified 17, 24, 27, 19, 19, and 22 full-length MIPs, respectively, in the genomes of six Phytophthora species, P. infestans, P. parasitica, P. sojae, P. ramorum, P. capsici, and P. cinnamomi. Phylogenetic analysis showed that the PhyMIPs formed a completely distinct clade from their counterparts in other taxa and were clustered into nine subgroups. Sequence and structural properties indicated that the primary selectivity-related constrictions, including aromatic arginine (ar/R) selectivity filter and Froger's positions in PhyMIPs were distinct from those in other taxa. The substitutions in the conserved Asn-Pro-Ala motifs in loops B and E of many PhyMIPs were also divergent from those in other taxonomic domains. The group-specific consensus sequences/ motifs deciphered in different loops and transmembrane α-helices of PhyMIPs were distinct from those in plants, animals, and other microbes. Conclusion: This study represents PhyMIPs with distinct evolutionary and structural properties, and the data collectively indicates that PhyMIPs might have novel functions.

The Knockout of Enterobactin-Related Gene in Pectobacterium atrosepticum Results in Reduced Stress Resistance and Virulence towards the Primed Plants.

Siderophores produced by microorganisms to scavenge iron from the environment have been shown to contribute to virulence and/or stress resistance of some plant pathogenic bacteria. Phytopathogenic bacteria of Pectobacterium genus possess genes for the synthesis of siderophore enterobactin, which role in plant-pathogen interactions has not been elucidated. In the present study we characterized the phenotype of the mutant strain of Pba deficient for the enterobactin-biosynthetic gene entA. We showed that enterobactin may be considered as a conditionally beneficial virulence factor of Pba. The entA knockout did not reduce Pba virulence on non-primed plants; however, salicylic acid-primed plants were more resistant to ΔentA mutant than to the wild type Pba. The reduced virulence of ΔentA mutant towards the primed plants is likely explained by its compromised resistance to oxidative stress.

LPMO-oxidized cellulose oligosaccharides evoke immunity in Arabidopsis conferring resistance towards necrotrophic fungus B. cinerea

Lytic Polysaccharide Monooxygenases (LPMOs) are powerful redox enzymes able to oxidatively cleave recalcitrant polysaccharides. Widely conserved across biological kingdoms, LPMOs of the AA9 family are deployed by phytopathogens to deconstruct cellulose polymers. In response, plants have evolved sophisticated mechanisms to sense cell wall damage and thus self-triggering Damage Triggered Immunity responses. Here, we show that Arabidopsis plants exposed to LPMO products triggered the innate immunity ultimately leading to increased resistance to the necrotrophic fungus Botrytis cinerea. We demonstrated that plants undergo a deep transcriptional reprogramming upon elicitation with AA9 derived cellulose- or cello-oligosaccharides (AA9_COS). To decipher the specific effects of native and oxidized LPMO-generated AA9_COS, a pairwise comparison with cellobiose, the smallest non-oxidized unit constituting cellulose, is presented. Moreover, we identified two leucine-rich repeat receptor-like kinases, namely STRESS INDUCED FACTOR 2 and 4, playing a crucial role in signaling the AA9_COS-dependent responses such as camalexin production. Furthermore, increased levels of ethylene, jasmonic and salicylic acid hormones, along with deposition of callose in the cell wall was observed. Collectively, our data reveal that LPMOs might play a crucial role in plant-pathogen interactions.

Mitogen-Activated Protein Kinase MAPKKK7 from Plasmodiophora brassicae Regulates Low-Light-Dependent Nicotiana benthamiana Immunity.

MAPKKK is the largest family of mitogen-activated protein kinase (MAPK) cascades and is known to play important roles in plant pathogen interaction by regulating fungal cell proliferation, growth, and pathogenicity. Thus far, only a few have been characterized because of the functional redundancy of MAPKKKs. In this study, it is interesting that Plasmodiophora brassicae (Pb)MAPKKK7 was clustered into the A3 subgroup of plant MAPKKKs by a phylogenetic analysis and also with the BCK1 and STE groups of fungal MAPKKKs. PbMAPKKK7 function in reactive oxygen species accumulation and cell death in Nicotiana benthamiana was characterized. Agroinfiltration with the PbMAPKKK7 mutated protein kinase domain relieved these changes. Interestingly, the induction of cell death was dependent on light intensity. Transcriptional profiling analysis demonstrated that PbMAPKKK7 was highly expressed during cortex infection stages, indicating its important role in P. brassicae infection. These functional analyses of PbMAPKKK7 build knowledge of new roles of the MAPK cascade pathway in N. benthamiana and P. brassicae interactions.

Seasonal and long-term consequences of esca grapevine disease on stem xylem integrity.

Hydraulic failure has been extensively studied during drought-induced plant dieback, but its role in plant-pathogen interactions is under debate. During esca, a grapevine (Vitis vinifera) disease, symptomatic leaves are prone to irreversible hydraulic dysfunctions but little is known about the hydraulic integrity of perennial organs over the short- and long-term. We investigated the effects of esca on stem hydraulic integrity in naturally infected plants within a single season and across season(s). We coupled direct (ks) and indirect (kth) hydraulic conductivity measurements, and tylose and vascular pathogen detection with in vivo X-ray microtomography visualizations. Xylem occlusions (tyloses) and subsequent loss of stem hydraulic conductivity (ks) occurred in all shoots with severe symptoms (apoplexy) and in more than 60% of shoots with moderate symptoms (tiger-stripe), with no tyloses in asymptomatic shoots. In vivo stem observations demonstrated that tyloses occurred only when leaf symptoms appeared, and resulted in more than 50% loss of hydraulic conductance in 40% of symptomatic stems, unrelated to symptom age. The impact of esca on xylem integrity was only seasonal, with no long-term impact of disease history. Our study demonstrated how and to what extent a vascular disease such as esca, affecting xylem integrity, could amplify plant mortality through hydraulic failure.

Host Cell Wall Damage during Pathogen Infection: Mechanisms of Perception and Role in Plant-Pathogen Interactions.

The plant cell wall (CW) is a complex structure that acts as a mechanical barrier, restricting the access to most microbes. Phytopathogenic microorganisms can deploy an arsenal of CW-degrading enzymes (CWDEs) that are required for virulence. In turn, plants have evolved proteins able to inhibit the activity of specific microbial CWDEs, reducing CW damage and favoring the accumulation of CW-derived fragments that act as damage-associated molecular patterns (DAMPs) and trigger an immune response in the host. CW-derived DAMPs might be a component of the complex system of surveillance of CW integrity (CWI), that plants have evolved to detect changes in CW properties. Microbial CWDEs can activate the plant CWI maintenance system and induce compensatory responses to reinforce CWs during infection. Recent evidence indicates that the CWI surveillance system interacts in a complex way with the innate immune system to fine-tune downstream responses and strike a balance between defense and growth.

Changes in the Plant β-Sitosterol/Stigmasterol Ratio Caused by the Plant Parasitic Nematode Meloidogyne incognita.

Sterols play a key role in various physiological processes of plants. Commonly, stigmasterol, β-sitosterol and campesterol represent the main plant sterols, and cholesterol is often reported as a trace sterol. Changes in plant sterols, especially in β-sitosterol/stigmasterol levels, can be induced by different biotic and abiotic factors. Plant parasitic nematodes, such as the root-knot nematode Meloidogyne incognita, are devastating pathogens known to circumvent plant defense mechanisms. In this study, we investigated the changes in sterols of agricultural important crops, Brassica juncea (brown mustard), Cucumis sativus (cucumber), Glycine max (soybean), Solanum lycopersicum (tomato) and Zea mays (corn), 21 days post inoculation (dpi) with M. incognita. The main changes affected the β-sitosterol/stigmasterol ratio, with an increase of β-sitosterol and a decrease of stigmasterol in S. lycopersicum, G. max, C. sativus and Z. mays. Furthermore, cholesterol levels increased in tomato, cucumber and corn, while cholesterol levels often were below the detection limit in the respective uninfected plants. To better understand the changes in the β-sitosterol/stigmasterol ratio, gene expression analysis was conducted in tomato cv. Moneymaker for the sterol 22C-desaturase gene CYP710A11, responsible for the conversion of β-sitosterol to stigmasterol. Our results showed that the expression of CYP710A11 was in line with the sterol profile of tomato after M. incognita infection. Since sterols play a key role in plant-pathogen interactions, this finding opens novel insights in plant nematode interactions.

Trehalose determination in Norway spruce (Picea abies) roots. Analytics matters

We present concise results of method validation for trehalose quantitation by LC-MS/MS in spruce ectomycorrhizal roots in order to describe spruce health status, mainly in connection to contamination by a pathogenic fungus, Gemmamyces piceae. The procedure is based on Rogatsky et al. (2005) developed for human plasma. We found out that the best extraction yield was achieved with 80% methanol/water (v/v) solution and optimal extraction temperature was set between 50-60°C. In contrast to previous papers, we minimized the activity of trehalase enzyme by putting root samples into liquid N2 immediately after root excavation, followed by freeze-drying in order to stop trehalase activity. Higher content of trehalose was recorded in healthy trees, confirming the idea that ectomycorrhiza plays a significant role in plant-pathogen interactions.

Diurnal, Circadian , and Photomorphogenic Analyses in Magnaporthe oryzae.

Circadian rhythms have been shown to play an important role in plant-pathogen interactions between plants and fungi. These protocols describe the methodology used to determine the function and characteristics of the diurnal and circadian behavior in the hemibiotrophic fungal pathogen, Magnaporthe oryzae. Here we describe methods to determine how conidiation, conidial development, and pathogenicity may be altered in M. oryzae as a result of differing diurnal or circadian environmental conditions.

Complete Chromosome-Scale Genome Sequence Resource for Sporisorium panici-leucophaei, the Causal Agent of Sourgrass Smut Disease.

Here, we present the first complete chromosome-level genome assembly of the smut fungus strain Sporisorium panici-leucophaei SPL10A, the causal agent of the sourgrass (Digitaria insularis) smut disease. Combining Illumina paired-end and Nanopore long reads, we generated a final assembly composed of 23 chromosomes (22 nuclear and one mitochondrial) with 18,915,934 bp. Gene prediction accomplished using extrinsic evidence from the sugarcane smut fungus Sporisorium scitamineum originated a total of 6,402 protein-encoding genes. The secretome (388 proteins) and the effectorome repertoires (68 candidates) were also predicted, given their crucial roles in plant-pathogen interactions. The complete telomere-to-telomere chromosome sequences of this poorly studied fungus will provide a valuable resource for future comparative genomic studies among smuts to unravel their underlying pathogenicity mechanisms.[Formula: see text] Copyright © 2021 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Effect of Submerging Solanum lycopersicum Roots in Salicylic Acid (SA) Solution for Different Durations on Nematode Infection and Expressions of SlPR5 Gene

Salicylic acid (SA) stimulates the mechanism of the plant defence and involves in a role in plant pathogen interactions. Plant parasitic nematodes are important biotic stresses causing negative effect on plant growth and development. Treatment of plant roots with SA may increase the plant defence mechanisms against biotic stresses. However, the treated effect of SA on plant defence mechanisms against a root-knot nematode, Meloidogyne incognita, has not been fully understood in terms of plant pathogen interactions. Therefore, this study was aimed to determine the most effective SA exposure time on increasing the plant defence and decreasing the nematode parasitism in Solanum lycopersicum. In addition, effects of SA treatment on the expression Pathogenesis Related Gene 5 (PR5) was evaluated. For this aim, tomato seedlings were exposed within 1000µM SA concentration with distinctive time durations. The expression of PR5 gene was accomplished using RT-PCR at 1, 3, 7, 14, 21 days post infection (dpi) for each sample. Root galling index, nematode number and reproduction rate were evaluated. Results revealed that nematode reproduction rate was decreased at in longer durations after SA treatment on roots. The highest nematode reproduction rate was determined in nematode+water (non-SA treatment) application compare to SA treatments. The highest increased level of expression of SlPR5 gene was determined in early (1 dpi) SA treatment + nematode infection. To conclude, SA treatment may increase the plant defence mechanisms and PR5 gene may involve in nematode-plant parasitism.

Cytidine-to-Uridine RNA Editing Factor NbMORF8 Negatively Regulates Plant Immunity to Phytophthora Pathogens.

Mitochondria and chloroplasts play key roles in plant-pathogen interactions. Cytidine-to-uridine (C-to-U) RNA editing is a critical posttranscriptional modification in mitochondria and chloroplasts that is specific to flowering plants. Multiple organellar RNA-editing factors (MORFs) form a protein family that participates in C-to-U RNA editing, but little is known regarding their immune functions. Here, we report the identification of NbMORF8, a negative regulator of plant immunity to Phytophthora pathogens. Using virus-induced gene silencing and transient expression in Nicotiana benthamiana, we show that NbMORF8 functions through the regulation of reactive oxygen species production, salicylic acid signaling, and accumulation of multiple Arg-X-Leu-Arg effectors of Phytophthora pathogens. NbMORF8 is localized to mitochondria and chloroplasts, and its immune function requires mitochondrial targeting. The conserved MORF box domain is not required for its immune function. Furthermore, we show that the preferentially mitochondrion-localized NbMORF proteins negatively regulate plant resistance against Phytophthora, whereas the preferentially chloroplast-localized ones are positive immune regulators. Our study reveals that the C-to-U RNA-editing factor NbMORF8 negatively regulates plant immunity to the oomycete pathogen Phytophthora and that mitochondrion- and chloroplast-localized NbMORF family members exert opposing effects on immune regulation.

RdDM pathway components differentially modulate Tobamovirus symptom development.

The crop yield losses induced by phytoviruses are mainly associated with the symptoms of the disease. DNA modifications as methylation can modulate the information coded by the sequence, process named epigenetics. Viral infection can change the expression patterns of different genes linked to defenses and symptoms. This work represents the initial step to expose the role of epigenetic process, in the production of symptoms associated with plants-virus interactions. Small RNAs (sRNAs) are important molecules for gene regulation in plants and play an essential role in plant-pathogen interactions. Researchers have evaluated the relationship between viral infections as well as the endogenous accumulation of sRNAs and the transcriptional changes associated with the production of symptoms, but little is known about a possible direct role of epigenetics, mediated by 24-nt sRNAs, in the induction of these symptoms. Using different RNA directed DNA methylation (RdDM) pathway mutants and a triple demethylase mutant; here we demonstrate that the disruption of RdDM pathway during viral infection produce alterations in the plant transcriptome and in consequence changes in plant symptoms. This study represents the initial step in exposing that DNA methylation directed by endogenous sRNAs has an important role, uncoupled to defense, in the production of symptoms associated with plant-virus interactions.

Apoplastic Cell Death-Inducing Proteins of Filamentous Plant Pathogens: Roles in Plant-Pathogen Interactions.

Filamentous pathogens, such as phytopathogenic oomycetes and fungi, secrete a remarkable diversity of apoplastic effector proteins to facilitate infection, many of which are able to induce cell death in plants. Over the past decades, over 177 apoplastic cell death-inducing proteins (CDIPs) have been identified in filamentous oomycetes and fungi. An emerging number of studies have demonstrated the role of many apoplastic CDIPs as essential virulence factors. At the same time, apoplastic CDIPs have been documented to be recognized by plant cells as pathogen-associated molecular patterns (PAMPs). The recent findings of extracellular recognition of apoplastic CDIPs by plant leucine-rich repeat-receptor-like proteins (LRR-RLPs) have greatly advanced our understanding of how plants detect them and mount a defense response. This review summarizes the latest advances in identifying apoplastic CDIPs of plant pathogenic oomycetes and fungi, and our current understanding of the dual roles of apoplastic CDIPs in plant-filamentous pathogen interactions.

Autophagy in Plant-Virus Interactions.

Autophagy is a conserved vacuole/lysosome-mediated degradation pathway for clearing and recycling cellular components including cytosol, macromolecules, and dysfunctional organelles. In recent years, autophagy has emerged to play important roles in plant-pathogen interactions. It acts as an antiviral defense mechanism in plants. Moreover, increasing evidence shows that plant viruses can manipulate, hijack, or even exploit the autophagy pathway to promote pathogenesis, demonstrating the pivotal role of autophagy in the evolutionary arms race between hosts and viruses. In this review, we discuss recent findings about the antiviral and proviral roles of autophagy in plant-virus interactions.

Lasiodiplodia theobromae-induced alteration in ROS metabolism and its relation to gummosis development in Prunus persica

Peach gummosis caused by Lasiodiplodia theobromae is one of the most detrimental diseases to peaches in southern China. Reactive oxygen species (ROS) play major roles in plant-pathogen interactions, however, their roles in the pathogenesis of peach gummosis, especially shoot disease in perennials, are largely unknown. In this study, the effects of L. theobromae on ROS production-scavenging systems and on signalling transduction during L. theobromae-induced gummosis in current-year peach shoots were investigated. The infection by L. theobromae led to a ROS burst and activated the plant antioxidant enzyme-dependent scavenging system. With disease progression, the capacity of the plant antioxidant machinery declined, and allowed for ROS accumulation and eventual malondialdehyde production. As for the fungus L. theobromae, the transcripts of genes related to ROS production were significantly repressed, and concomitantly the expression of genes related to antioxidant systems and oxidative stress resistance was markedly upregulated, perhaps to alleviate oxidative stress for successful colonisation. Moreover, genes involved in phytohormones biosynthesis and pathogenesis-related proteins were all markedly promoted, which could contribute to the restriction of disease development in peach shoots. Overall, the results showed that the ROS production-scavenging system in P. persica might affect disease development during peach-L. theobromae interaction. Our findings lay the foundations for future in-depth investigations of the molecular mechanisms and regulatory networks underlying L. theobromae-mediated shoot diseases in terms of ROS production-scavenging systems.

Cotton leaf curl Multan virus βC1 Protein Induces Autophagy by Disrupting the Interaction of Autophagy-Related Protein 3 with Glyceraldehyde-3-Phosphate Dehydrogenases.

Autophagy plays an important role in plant-pathogen interactions. Several pathogens including viruses induce autophagy in plants, but the underpinning mechanism remains largely unclear. Furthermore, in virus-plant interactions, viral factor(s) that induce autophagy have yet to be identified. Here, we report that the βC1 protein of Cotton leaf curl Multan betasatellite (CLCuMuB) interacts with cytosolic glyceraldehyde-3-phosphate dehydrogenase (GAPC), a negative autophagic regulator, to induce autophagy in Nicotiana benthamiana CLCuMuB βC1 bound to GAPCs and disrupted the interaction between GAPCs and autophagy-related protein 3 (ATG3). A mutant βC1 protein (βC13A) in which I45, Y48, and I53 were all substituted with Ala (A), had a dramatically reduced binding capacity with GAPCs, failed to disrupt the GAPCs-ATG3 interactions and failed to induce autophagy. Furthermore, mutant virus carrying βC13A showed increased symptoms and viral DNA accumulation associated with decreased autophagy in plants. These results suggest that CLCuMuB βC1 activates autophagy by disrupting GAPCs-ATG3 interactions.