Arabidopsis RNA polymerase II C-terminal domain phosphatase-like 1 targets mitogen-activated protein kinase cascades to suppress plant immunity

Mitogen-activated protein kinase (MAPK) cascades play pivotal roles in plant defense against phytopathogens downstream of immune receptor complexes. The amplitude and duration of MAPK activation must be strictly controlled, but the underlying mechanism remains unclear. Here, we identified Arabidopsis CPL1 (C-terminal domain phosphatase-like 1) as a negative regulator of microbe-associated molecular pattern (MAMP)-triggered immunity via a forward-genetic screen. Disruption of CPL1 significantly enhanced plant resistance to Pseudomonas pathogens induced by the bacterial peptide flg22. Furthermore, flg22-induced MPK3/MPK4/MPK6 phosphorylation was dramatically elevated in cpl1 mutants but severely impaired in CPL1 overexpression lines, suggesting that CPL1 might interfere with flg22-induced MAPK activation. Indeed, CPL1 directly interacted with MPK3 and MPK6, as well as the upstream MKK4 and MKK5. A firefly luciferase-based complementation assay indicated that the interaction between MKK4/MKK5 and MPK3/MPK6 was significantly reduced in the presence of CPL1. These results suggest that CPL1 plays a novel regulatory role in suppressing MAMP-induced MAPK cascade activation and MAMP-triggered immunity to bacterial pathogens.

Acetyl-Proteomic Profiling of Sorghum bicolor Seedlings after Chitin Treatment Reveals the Involvement of Acetylated Chlorophyll a/b Binding Proteins in the Innate Immune Response

Plant pathogen-associated molecular pattern-triggered immunity (PTI) is affected by post-translational modifications, but the role of acetylation in the PTI responses of Sorghum bicolor remains unclear. In this study, a comprehensive acetyl-proteomic analysis was performed on sorghum seedlings treated with chitin based on label-free protein quantification. Chitin rapidly induced 15 PTI-related genes and 5 defense enzymes. Acetylation was upregulated in sorghum after the chitin treatment, and 579, 895, and 929 acetylated proteins, peptides, and sites, respectively, were identified using high-performance liquid chromatography-tandem mass spectrometry. Acetylation and expression of chlorophyll a/b binding proteins (Lhcs) were significantly upregulated, and they were localized in chloroplasts. Additionally, we found that the expression of Lhcs in vivo enhanced chitin-mediated acetylation. The findings of this study provide a comprehensive assessment of the lysine acetylome in sorghum and a foundation for future study into the regulatory mechanisms of acetylation during chlorophyll synthesis.

Advances in protein glycosylation and its role in tissue repair and regeneration

After tissue damage, a series of molecular and cellular events are initiated to promote tissue repair and regeneration to restore its original structure and function. These events include inter-cell communication, cell proliferation, cell migration, extracellular matrix differentiation, and other critical biological processes. Glycosylation is the crucial conservative and universal post-translational modification in all eukaryotic cells [1], with influential roles in intercellular recognition, regulation, signaling, immune response, cellular transformation, and disease development. Studies have shown that abnormally glycosylation of proteins is a well-recognized feature of cancer cells, and specific glycan structures are considered markers of tumor development. There are many studies on gene expression and regulation during tissue repair and regeneration. Still, there needs to be more knowledge of complex carbohydrates' effects on tissue repair and regeneration, such as glycosylation. Here, we present a review of studies investigating protein glycosylation in the tissue repair and regeneration process.

PeVL1 Novel Elicitor Protein, from Verticillium lecanii 2, Enhances Systemic Resistance against Rice Leaf Roller (Marasmia ruralis Wlk.) in Rice (Oryza sativa L.)

The hazardous pest known as rice leaf roller (Marasmia ruralis Wlk.) (Lepidoptera: Pyralidae), which undermines rice (Oryza sativa L.) output globally, folds the leaves of the rice plant. Protein elicitors are thought to be biological elements that causes the rice to become resistant to herbivores. The potential for biocontrol of the emerging elicitor protein evaluated from Verticillium lecanii 2 (PeVL1) was evaluated against M. ruralis. To assess the impact of PeVL1 on immature development, survival, and lifetime, four different PeVL1 concentrations were allocated. Electrical penetration graphs (EPGs) against M. ruralis were used to evaluate adult reproductive efficiency and the interaction between the pest and the pathogen. Furthermore, the characterization of active substances in PeVL1 with multi-acting entomopathogenic effects looked into the direct interactions of PeVL1 with temperature and climatic change in rice (O. sativa) plants. PeVL1 treatments reduced the population increase of second and third generation M. ruralis compared to controls. In a test of host selection, M. ruralis colonized control plants more quickly than PeVL1-treated O. sativa plants. PeVL1 concentrations prolonged the M. ruralis larval stage. Similar to fecundity, PeVL1-treated seedlings produced fewer offspring than control seedlings. On PeVL1-treated leaves, trichomes and wax production created an unfavorable habitat for M. ruralis. PeVL1 changed the surface structure of the leaves, which inhibited colonization and decreased M. ruralis reproduction. The activation of pathways was another aspect of systemic defense activities including jasmonic acid (JA), salicylic acid (SA), and ethylene (ET). Based on these results against M. ruralis, the use of PeVL1 in the agroecosystem with integrated pest management and biocontrol seems appropriate. Our research provides a novel insight into a cutting-edge biocontrol method utilizing V. lecanii 2.

Biocontrol Potential of PeBL2, a Novel Entomopathogenic Bacterium from Brevibacillus laterosporus A60, Induces Systemic Resistance against Rice Leaf Folder Cnaphalocrocis exigua (Butler) in Rice (Oryza sativa L.)

The dangerous insect pest known as rice leaf folder Cnaphalocrocis exigua (Butler), which reduces rice output globally, twists and feeds on the young rice plant's leaves. Protein elicitors are hypothesized to be biological components that promote rice in becoming herbivore resistant. The evolving elicitor protein PeBL2, obtained from Brevibacillus laterosporus A60, was tested for biocontrol against C. exigua. Four distinct PeBL2 doses (74.23, 45.53, 22.26, and 11.13 μg mL^-1) were assigned to evaluate the impact of PeBL2 on immature growth, survivability, and lifespan. Adult reproductive efficiency and the interaction between the pest and the disease were assessed against C. exigua. Further, the assessment of active compounds in PeBL2 with multi-acting entomopathogenic effects investigated the direct correlations of PeBL2 with temperature and climatic change in plants of rice (Oryza sativa L.). When compared to controls, PeBL2 treatments reduced the growing population of second- and third-generation C. exigua. Cnaphalocrocis exigua colonized control plants faster than PeBL2-treated O. sativa plants in a host selection test. PeBL2 doses delayed the development of the larval stage of C. exigua. PeBL2-treated seedlings generated less offspring than control seedlings, identical to fecundity. Trichomes and wax formation on PeBL2-treated leaves generated an adverse environment for C. exigua. PeBL2 altered the surface topography of the leaves, preventing colonization and reducing C. exigua reproduction. PeBL2-treated O. sativa seedlings exhibited somewhat increased amounts of jasmonic acid (JA), salicylic acid (SA), and ethylene (ET). Systemic defensive processes also included the activation of pathways (JA, SA, and ET). Following these results versus C. exigua, the use of PeBL2 in an agroecosystem with integrated pest management and biocontrol appears to be reasonable. These findings shed new light on a cutting-edge biocontrol technique based on B. laterosporus A60.

Altering Microbiomes with Hydroxyapatite Nanoparticles: A Metagenomic Analysis

Hydroxyapatite (HAp), the most abundant biological material among mammals, has been recently demonstrated to possess moderate antibacterial properties. Metagenomics provides a series of tools for analyzing the simultaneous interaction of materials with larger communities of microbes, which may aid in optimizing the antibacterial activity of a material such as HAp. Here, a microbiome intrinsic to the sample of sandy soil collected from the base of an African Natal plum (Carissa macrocarpa) shrub surrounding the children's sandbox at the Arrowhead Park in Irvine, California was challenged with HAp nanoparticles and analyzed with next-generation sequencing for hypervariable 16S ribosomal DNA base pair homologies. HAp nanoparticles overwhelmingly reduced the presence of Gram-negative phyla, classes, orders, families, genera and species, and consequently elevated the relative presence of their Gram-positive counterparts. Thermodynamic, electrostatic and chemical bonding arguments were combined in a model proposed to explain this selective affinity. The ability of amphiphilic surface protrusions of lipoteichoic acid in Gram-positive bacteria and mycolic acid in mycobacteria to increase the dispersibility of the bacterial cells and assist in their resistance to capture by the solid phase is highlighted. Within the Gram-negative group, the variability of the distal, O-antigen portion of the membrane lipopolysaccharide was shown to be excessive and the variability of its proximal, lipid A portion insufficient to explain the selectivity based on chemical sequence arguments. Instead, flagella-driven motility proves to be a factor favoring the evasion of binding to HAp. HAp displayed a preference toward binding to less pathogenic bacteria than those causative of disease in humans, while taxa having a positive agricultural effect were largely captured by HAp, indicating an evolutionary advantage this may have given it as a biological material. The capacity to selectively sequester Gram-negative microorganisms and correspondingly alter the composition of the microbiome may open up a new avenue in environmental and biomedical applications of HAp.

DFT evaluation of structural, electronic and variation properties for complex carbohydrates with biological interest

The synthetic bicyclic bis(hemiacetals) compounds 1,5-pyranose-9,7-pyranoses, with a structural analogy to the bicyclic monosaccharide Bradyrhizose, have been described here based on a theoretical approach, using DFT calculations with the B3LYP functional combined with the 6-311 + G(d,p) basis set. First, we have performed a geometrical and electronic properties description of (1 R,9S), (1S,9S) and (1S,9R)-1,5-pyranose-9,7-pyranoses. Results analysis indicated that, slight differences in the three-dimensional orientations of their atoms lead to an enormous difference in chemical reactivity. Consequently, (1S,9S) and (1S,9R) isomers are predicted to be the most resembling the natural bradyrhizose in structural features. To enhance the performance of these two isomers, a set of modifications through functional groups attached to the reactive sites were determined by local reactivity descriptors. Subsequently, in order to get more information on the obtained derivatives for both isomers, HOMO, LUMO, Egap and four electronic parameters were calculated and compared. The substituted systems show a good performance in chemical reactivity than the unmodified parent compounds.Communicated by Ramaswamy H. Sarma.

Fungi hijack a ubiquitous plant apoplastic endoglucanase to release a ROS scavenging β-glucan decasaccharide to subvert immune responses

Plant pathogenic and beneficial fungi have evolved several strategies to evade immunity and cope with host-derived hydrolytic enzymes and oxidative stress in the apoplast, the extracellular space of plant tissues. Fungal hyphae are surrounded by an inner insoluble cell wall layer and an outer soluble extracellular polysaccharide (EPS) matrix. Here, we show by proteomics and glycomics that these two layers have distinct protein and carbohydrate signatures, and hence likely have different biological functions. The barley (Hordeum vulgare) β-1,3-endoglucanase HvBGLUII, which belongs to the widely distributed apoplastic glycoside hydrolase 17 family (GH17), releases a conserved β-1,3;1,6-glucan decasaccharide (β-GD) from the EPS matrices of fungi with different lifestyles and taxonomic positions. This low molecular weight β-GD does not activate plant immunity, is resilient to further enzymatic hydrolysis by β-1,3-endoglucanases due to the presence of three β-1,6-linked glucose branches and can scavenge reactive oxygen species. Exogenous application of β-GD leads to enhanced fungal colonization in barley, confirming its role in the fungal counter-defensive strategy to subvert host immunity. Our data highlight the hitherto undescribed capacity of this often-overlooked EPS matrix from plant-associated fungi to act as an outer protective barrier important for fungal accommodation within the hostile environment at the apoplastic plant-microbe interface.

Hrip1 Induces Systemic Resistance against Bean Aphid (Megoura japonica Matsumura) in Common Beans (Phaseolus vulgaris L.)

The emerging elicitor protein Hrip1 was evaluated for sublethal effects and biocontrol potential in the common bean Phaseolus vulgaris. In Megoura japonica Matsumura, purified elicitor protein Hrip1 was investigated for impacts on endurance, life expectancy, juvenile expansion, fully grown procreative performance, and pathogen–pest interface. The multi-acting entomopathogenic effects of the active compounds of Alternaria tenuissima active on Hrip1 in common bean (Phaseolus vulgaris L.) plants were also investigated. Megoura japonica population expansion was reduced by Hrip1 treatments (second and third generations). In a host selection test, control plants colonized quicker than Hrip1-treated P. vulgaris plants. Hrip1 influenced the longevity, development, and fertility of insects. Hrip1-elicitor protein concentrations aided M. japonica nymph development. Similarly, seedlings treated with Hrip1 generated fewer offspring than seedlings not treated with Hrip1. Hrip1 altered plant height and leaf surface structure, reducing M. japonica reproduction and colonization. Hrip1-treated P. vulgaris seedlings exhibited somewhat increased amounts of jasmonic acid, salicylic acid, and ethylene (ET). The integrated management of insect pests and biocontrol with Hrip1 in the agroecosystem appears to be suitable against M. japonica based on these findings.

A Comprehensive Overview of the Genes and Functions Required for Lettuce Infection by the Hemibiotrophic Phytopathogen Xanthomonas hortorum pv. vitians

The successful infection of a host plant by a phytopathogenic bacterium depends on a finely tuned molecular cross talk between the two partners. Thanks to transposon insertion sequencing techniques (Tn-seq), whole genomes can now be assessed to determine which genes are important for the fitness of several plant-associated bacteria in planta. Despite its agricultural relevance, the dynamic molecular interaction established between the foliar hemibiotrophic phytopathogen Xanthomonas hortorum pv. vitians and its host, lettuce (Lactuca sativa), remains completely unknown. To decipher the genes and functions mobilized by the pathogen throughout the infection process, we conducted a Tn-seq experiment in lettuce leaves to mimic the selective pressure occurring during natural infection. This genome-wide screening identified 170 genes whose disruption caused serious fitness defects in lettuce. A thorough examination of these genes using comparative genomics and gene set enrichment analyses highlighted that several functions and pathways were highly critical for the pathogen's survival. Numerous genes involved in amino acid, nucleic acid, and exopolysaccharide biosynthesis were critical. The xps type II secretion system operon, a few TonB-dependent transporters involved in carbohydrate or siderophore scavenging, and multiple genes of the carbohydrate catabolism pathways were also critical, emphasizing the importance of nutrition systems in a nutrient-limited environment. Finally, several genes implied in camouflage from the plant immune system and resistance to immunity-induced oxidative stress were strongly involved in host colonization. As a whole, these results highlight some of the central metabolic pathways and cellular functions critical for Xanthomonas host adaptation and pathogenesis. IMPORTANCE Xanthomonas hortorum was recently the subject of renewed interest, as several studies highlighted that its members were responsible for diseases in a wide range of plant species, including crops of agricultural relevance (e.g., tomato and carrot). Among X. hortorum variants, X. hortorum pv. vitians is a reemerging foliar hemibiotrophic phytopathogen responsible for severe outbreaks of bacterial leaf spot of lettuce all around the world. Despite recent findings, sustainable and practical means of disease control remain to be developed. Understanding the host-pathogen interaction from a molecular perspective is crucial to support these efforts. The genes and functions mobilized by X. hortorum pv. vitians during its interaction with lettuce had never been investigated. Our study sheds light on these processes by screening the whole pathogen genome for genes critical for its fitness during the infection process, using transposon insertion sequencing and comparative genomics.

The Xanthomonas RaxH-RaxR Two-Component Regulatory System Is Orthologous to the Zinc-Responsive Pseudomonas ColS-ColR System

Genome sequence comparisons to infer likely gene functions require accurate ortholog assignments. In Pseudomonas spp., the sensor-regulator ColS-ColR two-component regulatory system responds to zinc and other metals to control certain membrane-related functions, including lipid A remodeling. In Xanthomonas spp., three different two-component regulatory systems, RaxH-RaxR, VgrS-VgrR, and DetS-DetR, have been denoted as ColS-ColR in several different genome annotations and publications. To clarify these assignments, we compared the sensor periplasmic domain sequences and found that those from Pseudomonas ColS and Xanthomonas RaxH share a similar size as well as the location of a Glu-X-X-Glu metal ion-binding motif. Furthermore, we determined that three genes adjacent to raxRH are predicted to encode enzymes that remodel the lipid A component of lipopolysaccharide. The modifications catalyzed by lipid A phosphoethanolamine transferase (EptA) and lipid A 1-phosphatase (LpxE) previously were detected in lipid A from multiple Xanthomonas spp. The third gene encodes a predicted lipid A glycosyl transferase (ArnT). Together, these results indicate that the Xanthomonas RaxH-RaxR system is orthologous to the Pseudomonas ColS-ColR system that regulates lipid A remodeling. To avoid future confusion, we recommend that the terms ColS and ColR no longer be applied to Xanthomonas spp., and that the Vgr, Rax, and Det designations be used instead.

Unraveling the sugar code: the role of microbial extracellular glycans in plant-microbe interactions

To defend against microbial invaders but also to establish symbiotic programs, plants need to detect the presence of microbes through the perception of molecular signatures characteristic of a whole class of microbes. Among these molecular signatures, extracellular glycans represent a structurally complex and diverse group of biomolecules that has a pivotal role in the molecular dialog between plants and microbes. Secreted glycans and glycoconjugates such as symbiotic lipochitooligosaccharides or immunosuppressive cyclic β-glucans act as microbial messengers that prepare the ground for host colonization. On the other hand, microbial cell surface glycans are important indicators of microbial presence. They are conserved structures normally exposed and thus accessible for plant hydrolytic enzymes and cell surface receptor proteins. While the immunogenic potential of bacterial cell surface glycoconjugates such as lipopolysaccharides and peptidoglycan has been intensively studied in the past years, perception of cell surface glycans from filamentous microbes such as fungi or oomycetes is still largely unexplored. To date, only few studies have focused on the role of fungal-derived cell surface glycans other than chitin, highlighting a knowledge gap that needs to be addressed. The objective of this review is to give an overview on the biological functions and perception of microbial extracellular glycans, primarily focusing on their recognition and their contribution to plant-microbe interactions.

Protective plant immune responses are elicited by bacterial outer membrane vesicles

Bacterial outer membrane vesicles (OMVs) perform a variety of functions in bacterial survival and virulence. In mammalian systems, OMVs activate immune responses and are exploited as vaccines. However, little work has focused on the interactions of OMVs with plant hosts. Here, we report that OMVs from Pseudomonas syringae and P. fluorescens activate plant immune responses that protect against bacterial and oomycete pathogens. OMV-mediated immunomodulatory activity from these species displayed different sensitivity to biochemical stressors, reflecting differences in OMV content. Importantly, OMV-mediated plant responses are distinct from those triggered by conserved bacterial epitopes or effector molecules alone. Our study shows that OMV-induced protective immune responses are independent of the T3SS and protein, but that OMV-mediated seedling growth inhibition largely depends on proteinaceous components. OMVs provide a unique opportunity to understand the interplay between virulence and host response strategies and add a new dimension to consider in host-microbe interactions.

The role that bacterial outer membrane vesicles (OMVs) play in plant-microbe interactions is poorly characterized. McMillan et al. show that OMVs elicit plant immune responses that protect against pathogens. This study also reveals a use for OMVs as tools to probe the plant immune system.

Genome-Wide Analysis of LysM-Containing Gene Family in Wheat: Structural and Phylogenetic Analysis during Development and Defense

The lysin motif (LysM) family comprise a number of defense proteins that play important roles in plant immunity. The LysM family includes LysM-containing receptor-like proteins (LYP) and LysM-containing receptor-like kinase (LYK). LysM generally recognizes the chitin and peptidoglycan derived from bacteria and fungi. Approximately 4000 proteins with the lysin motif (Pfam PF01476) are found in prokaryotes and eukaryotes. Our study identified 57 LysM genes and 60 LysM proteins in wheat and renamed these genes and proteins based on chromosome distribution. According to the phylogenetic and gene structure of intron-exon distribution analysis, the 60 LysM proteins were classified into seven groups. Gene duplication events had occurred among the LysM family members during the evolution process, resulting in an increase in the LysM gene family. Synteny analysis suggested the characteristics of evolution of the LysM family in wheat and other species. Systematic analysis of these species provided a foundation of LysM genes in crop defense. A comprehensive analysis of the expression and cis-elements of LysM gene family members suggested that they play an essential role in defending against plant pathogens. The present study provides an overview of the LysM family in the wheat genome as well as information on systematic, phylogenetic, gene duplication, and intron-exon distribution analyses that will be helpful for future functional analysis of this important protein family, especially in Gramineae species.

Identifying candidate Aspergillus pathogenicity factors by annotation frequency

BACKGROUND

Members of the genus Aspergillus display a variety of lifestyles, ranging from saprobic to pathogenic on plants and/or animals. Increased genome sequencing of economically important members of the genus permits effective use of "-omics" comparisons between closely related species and strains to identify candidate genes that may contribute to phenotypes of interest, especially relating to pathogenicity. Protein-coding genes were predicted from 216 genomes of 12 Aspergillus species, and the frequencies of various structural aspects (exon count and length, intron count and length, GC content, and codon usage) and functional annotations (InterPro, Gene Ontology, and Kyoto Encyclopedia of Genes and Genomes terms) were compared.

RESULTS

Using principal component analyses, the three sets of functional annotations for each strain were clustered by species. The species clusters appeared to separate by pathogenicity on plants along the first dimensions, which accounted for over 20% of the variance. More annotations for genes encoding pectinases and secondary metabolite biosynthetic enzymes were assigned to phytopathogenic strains from species such as Aspergillus flavus. In contrast, Aspergillus fumigatus strains, which are pathogenic to animals but not plants, were assigned relatively more terms related to phosphate transferases, and carbohydrate and amino-sugar metabolism. Analyses of publicly available RNA-Seq data indicated that one A. fumigatus protein among 17 amino-sugar processing candidates, a hexokinase, was up-regulated during co-culturing with human immune system cells.

CONCLUSION

Genes encoding hexokinases and other proteins of interest may be subject to future manipulations to further refine understanding of Aspergillus pathogenicity factors.

Mechanistic insights into host adaptation, virulence and epidemiology of the phytopathogen Xanthomonas

Xanthomonas is a well-studied genus of bacterial plant pathogens whose members cause a variety of diseases in economically important crops worldwide. Genomic and functional studies of these phytopathogens have provided significant understanding of microbial-host interactions, bacterial virulence and host adaptation mechanisms including microbial ecology and epidemiology. In addition, several strains of Xanthomonas are important as producers of the extracellular polysaccharide, xanthan, used in the food and pharmaceutical industries. This polymer has also been implicated in several phases of the bacterial disease cycle. In this review, we summarise the current knowledge on the infection strategies and regulatory networks controlling virulence and adaptation mechanisms from Xanthomonas species and discuss the novel opportunities that this body of work has provided for disease control and plant health.

Sporulation in Ashbya gossypii

Ashbya gossypii is a filamentous ascomycete belonging to the yeast family of Saccharomycetaceae. At the end of its growth phase Ashbya generates abundant amounts of riboflavin and spores that form within sporangia derived from fragmented cellular compartments of hyphae. The length of spores differs within species of the genus. Needle-shaped Ashbya spores aggregate via terminal filaments. A. gossypii is a homothallic fungus which may possess a and α mating types. However, the solo-MATa type strain is self-fertile and sporulates abundantly apparently without the need of prior mating. The central components required for the regulation of sporulation, encoded by IME1, IME2, IME4, KAR4, are conserved with Saccharomyces cerevisiae. Nutrient depletion generates a strong positive signal for sporulation via the cAMP-PKA pathway and SOK2, which is also essential for sporulation. Strong inhibitors of sporulation besides mutations in the central regulatory genes are the addition of exogenous cAMP or the overexpression of the mating type gene MATα2. Sporulation has been dissected using gene-function analyses and global RNA-seq transcriptomics. This revealed a role of Msn2/4, another potential PKA-target, for spore wall formation and a key dual role of the protein A kinase Tpk2 at the onset of sporulation as well as for breaking the dormancy of spores to initiate germination. Recent work has provided an overview of ascus development, regulation of sporulation and spore maturation. This will be summarized in the current review with a focus on the central regulatory genes. Current research and open questions will also be discussed.

Prospects of Gene Knockouts in the Functional Study of MAMP-Triggered Immunity: A Review

Plants depend on both preformed and inducible defence responses to defend themselves against biotic stresses stemming from pathogen attacks. In this regard, plants perceive pathogenic threats from the environment through pattern recognition receptors (PRRs) that recognise microbe-associated molecular patterns (MAMPs), and so induce plant defence responses against invading pathogens. Close to thirty PRR proteins have been identified in plants, however, the molecular mechanisms underlying MAMP perception by these receptors/receptor complexes are not fully understood. As such, knockout (KO) of genes that code for PRRs and co-receptors/defence-associated proteins is a valuable tool to study plant immunity. The loss of gene activity often causes changes in the phenotype of the model plant, allowing in vivo studies of gene function and associated biological mechanisms. Here, we review the functions of selected PRRs, brassinosteroid insensitive 1 (BRI1) associated receptor kinase 1 (BAK1) and other associated defence proteins that have been identified in plants, and also outline KO lines generated by T-DNA insertional mutagenesis as well as the effect on MAMP perception—and triggered immunity (MTI). In addition, we further review the role of membrane raft domains in flg22-induced MTI in Arabidopsis, due to the vital role in the activation of several proteins that are part of the membrane raft domain theory in this regard.

Characterization of biopolymers produced by planktonic and biofilm cells of Herbaspirillum lusitanum P6-12

AIMS

The goal of this study was to characterize biopolymers from two modes of the Herbaspirillum lusitanum P6-12 growth: planktonic, in which cells are free swimming, and biofilm life style, in which the cells are sessile.

METHODS AND RESULTS

Differences in biopolymers composition from planktonic and biofilm cells of H. lusitanum strain P6-12 were analysed using Fourier transform infrared spectroscopy (FTIR), sodium dodecyl sulphate-polyacrylamide gel electrophoresis, gas-liquid chromatography and spectrophotometry. A high degree of polymer separation and purification was achieved by ultracentrifugation, and column chromatography allowed us to identify the chemical differences between biopolymers from biofilm and planktonic H. lusitanum. It was shown that planktonic cells of H. lusitanum P6-12 when cultivated in a liquid medium to the end of the exponential phase of growth, produced two high-molecular-weight glycoconjugates (were arbitrarily called CPS-I and CPS-II) of a lipopolysaccharide (LPS) nature and a lipid-polysacharide complex (were arbitrarily called EPS). The EPS, CPS-I, CPS-II had different monosaccharide and lipid compositions. The extracellular polymeric matrix (EPM) produced by the biofilm cells was mostly proteinaceous, with a small amount of carbohydrates (up to 3%). From the biofilm culture medium, a free extracellular polymeric substance (was arbitrarily called fEPS) was obtained that contained proteins and carbohydrates (up to 7%). The cells outside the biofilm had capsules containing high-molecular-weight glycoconjugate (was arbitrarily called CPS_FBC ) that consisted of carbohydrates (up to 10%), proteins (up to 16%) and lipids (up to 70%).

CONCLUSIONS

During biofilm formation, the bacteria secreted surface biopolymers that differed from those of the planktonic cells. The heterogeneity of the polysaccharide containing biopolymers of the H. lusitanum P6-12 surface is probably conditioned by their different functions in plant colonization and formation of an efficient symbiosis, as well as in cell adaptation to existence in plant tissues.

SIGNIFICANCE AND IMPACT OF THE STUDY

The results of the study permit a better understanding of the physiological properties of the biopolymers, for example, in plant-microbe interactions.

Elicitor and Receptor Molecules: Orchestrators of Plant Defense and Immunity

Pathogen-associated molecular patterns (PAMPs), microbe-associated molecular patterns (MAMPs), herbivore-associated molecular patterns (HAMPs), and damage-associated molecular patterns (DAMPs) are molecules produced by microorganisms and insects in the event of infection, microbial priming, and insect predation. These molecules are then recognized by receptor molecules on or within the plant, which activates the defense signaling pathways, resulting in plant’s ability to overcome pathogenic invasion, induce systemic resistance, and protect against insect predation and damage. These small molecular motifs are conserved in all organisms. Fungi, bacteria, and insects have their own specific molecular patterns that induce defenses in plants. Most of the molecular patterns are either present as part of the pathogen’s structure or exudates (in bacteria and fungi), or insect saliva and honeydew. Since biotic stresses such as pathogens and insects can impair crop yield and production, understanding the interaction between these organisms and the host via the elicitor–receptor interaction is essential to equip us with the knowledge necessary to design durable resistance in plants. In addition, it is also important to look into the role played by beneficial microbes and synthetic elicitors in activating plants’ defense and protection against disease and predation. This review addresses receptors, elicitors, and the receptor–elicitor interactions where these components in fungi, bacteria, and insects will be elaborated, giving special emphasis to the molecules, responses, and mechanisms at play, variations between organisms where applicable, and applications and prospects.

Tyrosine phosphorylation of the lectin receptor-like kinase LORE regulates plant immunity

Plant pattern recognition receptors (PRRs) perceive pathogen-associated molecular patterns (PAMPs) to activate immune responses. Medium-chain 3-hydroxy fatty acids (mc-3-OH-FAs), which are widely present in Gram-negative bacteria, were recently shown to be novel PAMPs in Arabidopsis thaliana. The Arabidopsis PRR LIPOOLIGOSACCHARIDE-SPECIFIC REDUCED ELICITATION (LORE) is a G-type lectin receptor-like kinase that recognizes mc-3-OH-FAs and subsequently mounts an immune response; however, the mechanisms underlying LORE activation and downstream signaling are unexplored. Here, we report that one of the mc-3-OH-FAs, 3-OH-C10:0, induces phosphorylation of LORE at tyrosine residue 600 (Y600). Phosphorylated LORE subsequently trans-phosphorylates the receptor-like cytoplasmic kinase PBL34 and its close paralogs, PBL35 and PBL36, and therefore activates plant immunity. Phosphorylation of LORE Y600 is required for downstream phosphorylation of PBL34, PBL35, and PBL36. However, the Pseudomonas syringae effector HopAO1 targets LORE, dephosphorylating the tyrosine-phosphorylated Y600 and therefore suppressing the immune response. These observations uncover the mechanism by which LORE mediates signaling in response to 3-OH-C10:0 in Arabidopsis.

Apoplastic invasion patterns triggering plant immunity: plasma membrane sensing at the frontline

Plants are able to effectively cope with invading pathogens by activating an immune response based on the detection of invasion patterns (IPs) originating from the pathogen or released by the plant after infection. At a first level, this perception takes place at the plasma membrane through cell surface immune receptors and although the involvement of proteinaceous pattern recognition receptors (PRRs) is well established, increasing data are also pointing out the role of membrane lipids in the sensing of IPs. In this review, we discuss the evolution of various conceptual models describing plant immunity and present an overview of well-characterized IPs from different natures and origins. We summarize the current knowledge on how they are perceived by plants at the plasma membrane, highlighting the increasingly apparent diversity of sentinel-related systems in plants.

Human protein paucimannosylation: cues from the eukaryotic kingdoms

Paucimannosidic proteins (PMPs) are bioactive glycoproteins carrying truncated α- or β-mannosyl-terminating asparagine (N)-linked glycans widely reported across the eukaryotic domain. Our understanding of human PMPs remains limited, despite findings documenting their existence and association with human disease glycobiology. This review comprehensively surveys the structures, biosynthetic routes and functions of PMPs across the eukaryotic kingdoms with the aim of synthesising an improved understanding on the role of protein paucimannosylation in human health and diseases. Convincing biochemical, glycoanalytical and biological data detail a vast structural heterogeneity and fascinating tissue- and subcellular-specific expression of PMPs within invertebrates and plants, often comprising multi-α1,3/6-fucosylation and β1,2-xylosylation amongst other glycan modifications and non-glycan substitutions e.g. O-methylation. Vertebrates and protists express less-heterogeneous PMPs typically only comprising variable core fucosylation of bi- and trimannosylchitobiose core glycans. In particular, the Manα1,6Manβ1,4GlcNAc(α1,6Fuc)β1,4GlcNAcβAsn glycan (M2F) decorates various human neutrophil proteins reportedly displaying bioactivity and structural integrity demonstrating that they are not degradation products. Less-truncated paucimannosidic glycans (e.g. M3F) are characteristic glycosylation features of proteins expressed by human cancer and stem cells. Concertedly, these observations suggest the involvement of human PMPs in processes related to innate immunity, tumorigenesis and cellular differentiation. The absence of human PMPs in diverse bodily fluids studied under many (patho)physiological conditions suggests extravascular residence and points to localised functions of PMPs in peripheral tissues. Absence of PMPs in Fungi indicates that paucimannosylation is common, but not universally conserved, in eukaryotes. Relative to human PMPs, the expression of PMPs in plants, invertebrates and protists is more tissue-wide and constitutive yet, similar to their human counterparts, PMP expression remains regulated by the physiology of the producing organism and PMPs evidently serve essential functions in development, cell-cell communication and host-pathogen/symbiont interactions. In most PMP-producing organisms, including humans, the N-acetyl-β-hexosaminidase isoenzymes and linkage-specific α-mannosidases are glycoside hydrolases critical for generating PMPs via N-acetylglucosaminyltransferase I (GnT-I)-dependent and GnT-I-independent truncation pathways. However, the identity and structure of many species-specific PMPs in eukaryotes, their biosynthetic routes, strong tissue- and development-specific expression, and diverse functions are still elusive. Deep exploration of these PMP features involving, for example, the characterisation of endogenous PMP-recognising lectins across a variety of healthy and N-acetyl-β-hexosaminidase-deficient human tissue types and identification of microbial adhesins reactive to human PMPs, are amongst the many tasks required for enhanced insight into the glycobiology of human PMPs. In conclusion, the literature supports the notion that PMPs are significant, yet still heavily under-studied biomolecules in human glycobiology that serve essential functions and create structural heterogeneity not dissimilar to other human N-glycoprotein types. Human PMPs should therefore be recognised as bioactive glycoproteins that are distinctly different from the canonical N-glycoprotein classes and which warrant a more dedicated focus in glycobiological research.

NINJA-associated ERF19 negatively regulates Arabidopsis pattern-triggered immunity

Recognition of microbe-associated molecular patterns (MAMPs) derived from invading pathogens by plant pattern recognition receptors (PRRs) initiates a subset of defense responses known as pattern-triggered immunity (PTI). Transcription factors (TFs) orchestrate the onset of PTI through complex signaling networks. Here, we characterized the function of ERF19, a member of the Arabidopsis thaliana ethylene response factor (ERF) family. ERF19 was found to act as a negative regulator of PTI against Botrytis cinerea and Pseudomonas syringae. Notably, overexpression of ERF19 increased plant susceptibility to these pathogens and repressed MAMP-induced PTI outputs. In contrast, expression of the chimeric dominant repressor ERF19-SRDX boosted PTI activation, conferred increased resistance to the fungus B. cinerea, and enhanced elf18-triggered immunity against bacteria. Consistent with a negative role for ERF19 in PTI, MAMP-mediated growth inhibition was weakened or augmented in lines overexpressing ERF19 or expressing ERF19-SRDX, respectively. Using biochemical and genetic approaches, we show that the transcriptional co-repressor Novel INteractor of JAZ (NINJA) associates with and represses the function of ERF19. Our work reveals ERF19 as a novel player in the mitigation of PTI, and highlights a potential role for NINJA in fine-tuning ERF19-mediated regulation of Arabidopsis innate immunity.

Dual function of a secreted fungalysin metalloprotease in Ustilago maydis

Fungalysins from several phytopathogenic fungi have been shown to be involved in cleavage of plant chitinases. While fungal chitinases are responsible for cell wall remodeling during growth and morphogenesis, plant chitinases are important components of immunity. This study describes a dual function of the Ustilago maydis fungalysin UmFly1 in modulation of both plant and fungal chitinases. Genetic, biochemical and microscopic experiments were performed to elucidate the in vitro and in planta functions of U. maydis UmFly1. U. maydis ∆umfly1 mutants show significantly reduced virulence, which coincides with reduced cleavage of the maize chitinase ZmChiA within its chitin-binding domain. Moreover, deletion of umfly1 affected the cell separation of haploid U. maydis sporidia. This phenotype is associated with posttranslational activation of the endogenous chitinase UmCts1. Genetic complementation of the ∆umfly1 mutant with a homologous gene from closely related, but nonpathogenic, yeast fully rescued the cell separation defect in vitro, but it could not recover the ∆umfly1 defect in virulence and cleavage of the maize chitinase. We report on the dual function of the secreted fungalysin UmFly1. We hypothesize that co-evolution of U. maydis with its host plant extended the endogenous function of UmFly1 towards the modulation of plant chitinase activity to promote infection.

Solid State NMR Studies of Intact Lipopolysaccharide Endotoxin

Lipopolysaccharides (LPS) are complex glycolipids forming the outside layer of Gram-negative bacteria. Their hydrophobic and heterogeneous nature greatly hampers their structural study in an environment similar to the bacterial surface. We have studied LPS purified from E. coli and pathogenic P. aeruginosa with long O-antigen polysaccharides assembled in solution as vesicles or elongated micelles. Solid-state NMR with magic-angle spinning permitted the identification of NMR signals arising from regions with different flexibilities in the LPS, from the lipid components to the O-antigen polysaccharides. Atomic scale data on the LPS enabled the study of the interaction of gentamicin antibiotic bound to P. aeruginosa LPS, for which we could confirm that a specific oligosaccharide is involved in the antibiotic binding. The possibility to study LPS alone and bound to a ligand when it is assembled in membrane-like structures opens great prospects for the investigation of proteins and antibiotics that specifically target such an important molecule at the surface of Gram-negative bacteria.

LysM1 in MmLYK2 is a motif required for the interaction of MmLYP1 and MmLYK2 in the chitin signaling

Two LysM-containing proteins, namely, MmLYP1 and MmLYK2, were identified in mulberry. These proteins might be involved in chitin signaling. The LysM1 of MmLYK2 is critical for their interactions. Chitin is a major component of fungal cell walls and acts as an elicitor in plant innate immunity. Lysin motif (LysM)-containing proteins are essential for chitin recognition. However, related studies have been rarely reported in woody plants. In this study, in mulberry, the expression of a LysM-containing protein, MmLYP1, was significantly up-regulated after treatment with chitin and pathogenic fungi. In addition, MmLYP1 has an affinity for insoluble chitin polymers. Thus, MmLYP1 might function in chitin signaling. Since MmLYP1 lacks an intracellular domain, additional protein kinases are required for this signaling. An LysM-containing kinase, MmLYK2, was then identified. Expression of the MmLYK2 did not change significantly after chitin treatment, and the affinity of MmLYK2 for insoluble chitin was not high. The structure of MmLYP1 is similar to that of the chitin elicitor-binding proteins in rice and Arabidopsis. However, MmLYK2 has two LysM motifs, while the chitin elicitor receptor kinase 1 proteins in rice and Arabidopsis have one and three LysM motifs, respectively. The LysM1 of MmLYK2 interacted with all four LysM motifs in MmLYP1 and MmLYK2 in yeast. The chimera lacking the LysM1 of MmLYK2 did not interact with MmLYP1 and MmLYK2 in yeast and Nicotiana benthamiana cells. The LysM1 in MmLYK2 is the key motif in the interaction between MmLYP1 and MmLYK2, which may be involved in chitin signaling.

Glycans as Modulators of Plant Defense Against Filamentous Pathogens

Plants and microbes utilize glycoconjugates as structural entities, energy reserves for cellular processes, and components of cellular recognition or binding events. The structural heterogeneity of carbohydrates in such systems is a result of the ability of the carbohydrate biosynthetic enzymes to reorient sugar monomers in a variety of forms, generating highly complex, linear, branched, or hierarchical structures. During the interaction between plants and their microbial pathogens, the microbial cell surface glycans, cell wall derived glycans, and glycoproteins stimulate the signaling cascades of plant immune responses, through a series of specific or broad spectrum recognition events. The microbial glycan-induced plant immune responses and the downstream modifications observed in host-plant glycan structures that combat the microbial attack have garnered immense interest among scientists in recent times. This has been enabled by technological advancements in the field of glycobiology, making it possible to study the ongoing co-evolution of the microbial and the corresponding host glycan structures, in greater detail. The new glycan analogs emerging in this evolutionary arms race brings about a fresh perspective to our understanding of plant-pathogen interactions. This review discusses the role of diverse classes of glycans and their derivatives including simple sugars, oligosaccharides, glycoproteins, and glycolipids in relation to the activation of classical Pattern-Triggered Immunity (PTI) and Effector-Triggered Immunity (ETI) defense responses in plants. While primarily encompassing the biological roles of glycans in modulating plant defense responses, this review categorizes glycans based on their structure, thereby enabling parallels to be drawn to other areas of glycobiology. Further, we examine how these molecules are currently being used to develop new bio-active molecules, potent as priming agents to stimulate plant defense response and as templates for designing environmentally friendly foliar sprays for plant protection.

Genome-wide identification and expression analysis of chitinase gene family in Brassica rapa reveals its role in clubroot resistance

Chitinases, a category of pathogenesis-related proteins, are responsible for catalyzing the hydrolysis of chitin into the N-acetyl-d-glucosamine. Therefore, chitinases are believed to function as a guardian against chitin-containing pathogens. Here, we examined the role of the Brassica rapa chitinase family genes in clubroot disease. A total of 33 chitinase genes were identified and grouped into five classes based on their conserved domain. They were distributed unevenly across eight chromosomes in B. rapa, and 31 of them contained few introns (≤2). In addition, the expression of these genes was organ-specific, and 14 genes were expressed differentially in response to Plasmodiophora brassicae challenge of clubroot-susceptible (CS NIL) and resistant (CR NIL) lines. Furthermore, reduced pathogen DNA content and clubroot symptoms were observed in the CS NILs after their treatment with chitin oligosaccharides 24 h prior to inoculation with P. brassicae. The findings indicate that chitinases play a crucial role in pathogen resistance of the host plants. The results offer an insight into the role of chitinase in B. rapa-P. brassicae interaction.

Signaling through plant lectins: modulation of plant immunity and beyond

Lectins constitute an abundant group of proteins that are present throughout the plant kingdom. Only recently, genome-wide screenings have unraveled the multitude of different lectin sequences within one plant species. It appears that plants employ a plurality of lectins, though relatively few lectins have already been studied and functionally characterized. Therefore, it is very likely that the full potential of lectin genes in plants is underrated. This review summarizes the knowledge of plasma membrane-bound lectins in different biological processes (such as recognition of pathogen-derived molecules and symbiosis) and illustrates the significance of soluble intracellular lectins and how they can contribute to plant signaling. Altogether, the family of plant lectins is highly complex with an enormous diversity in biochemical properties and activities.

OsCERK1 plays a crucial role in the lipopolysaccharide-induced immune response of rice

Plant cell surface receptor-like kinases (RLKs) mediate the signals from microbe-associated molecular patterns (MAMPs) that induce immune responses. Lipopolysaccharide (LPS), the major constituent of the outer membrane of gram-negative bacteria, is a common MAMP perceived by animals and plants; however, the plant receptors/co-receptors are unknown except for LORE, a bulb-type lectin S-domain RLK (B-lectin SD1-RLK) in Arabidopsis. OsCERK1 is a multifunctional RLK in rice that contains lysin motifs (LysMs) and is essential for the perception of chitin, a fungal MAMP, and peptidoglycan, a bacterial MAMP. Here, we analyzed the relevance of OsCERK1 to LPS perception in rice. Using OsCERK1-knockout mutants (oscerk1), we evaluated hydrogen peroxide (H₂ O₂ ) production and gene expression after LPS treatment. We also examined the LPS response in knockout mutants for the B-lectin SD1-RLK genes in rice and for all LysM-protein genes in Arabidopsis. Compared with wild-type rice cells, LPS responses in oscerk1 cells were mostly diminished. By contrast, rice lines mutated in either of three B-lectin SD1-RLK genes and Arabidopsis lines mutated in the LysM-protein genes responded normally to LPS. From these results, we conclude that OsCERK1 is an LPS receptor/co-receptor and that the LPS perception systems of rice and Arabidopsis are significantly different.

A conserved fungal glycosyltransferase facilitates pathogenesis of plants by enabling hyphal growth on solid surfaces

Pathogenic fungi must extend filamentous hyphae across solid surfaces to cause diseases of plants. However, the full inventory of genes which support this is incomplete and many may be currently concealed due to their essentiality for the hyphal growth form. During a random T-DNA mutagenesis screen performed on the pleomorphic wheat (Triticum aestivum) pathogen Zymoseptoria tritici, we acquired a mutant unable to extend hyphae specifically when on solid surfaces. In contrast "yeast-like" growth, and all other growth forms, were unaffected. The inability to extend surface hyphae resulted in a complete loss of virulence on plants. The affected gene encoded a predicted type 2 glycosyltransferase (ZtGT2). Analysis of >800 genomes from taxonomically diverse fungi highlighted a generally widespread, but discontinuous, distribution of ZtGT2 orthologues, and a complete absence of any similar proteins in non-filamentous ascomycete yeasts. Deletion mutants of the ZtGT2 orthologue in the taxonomically un-related fungus Fusarium graminearum were also severely impaired in hyphal growth and non-pathogenic on wheat ears. ZtGT2 expression increased during filamentous growth and electron microscopy on deletion mutants (ΔZtGT2) suggested the protein functions to maintain the outermost surface of the fungal cell wall. Despite this, adhesion to leaf surfaces was unaffected in ΔZtGT2 mutants and global RNAseq-based gene expression profiling highlighted that surface-sensing and protein secretion was also largely unaffected. However, ΔZtGT2 mutants constitutively overexpressed several transmembrane and secreted proteins, including an important LysM-domain chitin-binding virulence effector, Zt3LysM. ZtGT2 likely functions in the synthesis of a currently unknown, potentially minor but widespread, extracellular or outer cell wall polysaccharide which plays a key role in facilitating many interactions between plants and fungi by enabling hyphal growth on solid matrices.

Differential Interaction of Synthetic Glycolipids with Biomimetic Plasma Membrane Lipids Correlates with the Plant Biological Response

Natural and synthetic amphiphilic molecules including lipopeptides, lipopolysaccharides, and glycolipids are able to induce defense mechanisms in plants. In the present work, the perception of two synthetic C14 rhamnolipids, namely, Alk-RL and Ac-RL, differing only at the level of the lipid tail terminal group have been investigated using biological and biophysical approaches. We showed that Alk-RL induces a stronger early signaling response in tobacco cell suspensions than does Ac-RL. The interactions of both synthetic RLs with simplified biomimetic membranes were further analyzed using experimental and in silico approaches. Our results indicate that the interactions of Alk-RL and Ac-RL with lipids were different in terms of insertion and molecular responses and were dependent on the lipid composition of model membranes. A more favorable insertion of Alk-RL than Ac-RL into lipid membranes is observed. Alk-RL forms more stable molecular assemblies than Ac-RL with phospholipids and sterols. At the molecular level, the presence of sterols tends to increase the RLs' interaction with lipid bilayers, with a fluidizing effect on the alkyl chains. Taken together, our findings suggest that the perception of these synthetic RLs at the membrane level could be related to a lipid-driven process depending on the organization of the membrane and the orientation of the RLs within the membrane and is correlated with the induction of early signaling responses in tobacco cells.

Chemical and biological properties of the novel exopolysaccharide produced by a probiotic strain of Bifidobacterium longum

Bifidobacterium longum W11 is a commercialized probiotic that has an exopolysaccharide (EPS) layer covering its surface which could play a role in the beneficial properties attributed to the strain; thus, we have carried out chemical and biological analyses of this polymer. The eps cluster putatively involved in the polymer synthesis presented a unique structural organization not previously reported in bifidobacteria. B. longum W11 produced a complex polysaccharide blend with the main component composed of glucose and galactose. An exhaustive structural analysis identified two different repeating units: one linear [→6)-β-Galf-(1→3)-α-Galp-(1→] and one, more abundant, with the same backbone in which the β-Galf is 5-substituted by a β-Glcp unit. The antioxidant capability and the lack of toxicity of the whole EPS W11 mixture, as well as some functional characteristics of the producing strain, such as the in vitro resistance to gastrointestinal conditions and the adhesion of colonocytes, were also determined.

Proteomics-based identification of differentially abundant proteins reveals adaptation mechanisms of Xanthomonas citri subsp. citri during Citrus sinensis infection

BACKGROUND

Xanthomonas citri subsp. citri (Xac) is the causal agent of citrus canker. A proteomic analysis under in planta infectious and non-infectious conditions was conducted in order to increase our knowledge about the adaptive process of Xac during infection.

RESULTS

For that, a 2D-based proteomic analysis of Xac at 1, 3 and 5 days after inoculation, in comparison to Xac growth in NB media was carried out and followed by MALDI-TOF-TOF identification of 124 unique differentially abundant proteins. Among them, 79 correspond to up-regulated proteins in at least one of the three stages of infection. Our results indicate an important role of proteins related to biofilm synthesis, lipopolysaccharides biosynthesis, and iron uptake and metabolism as possible modulators of plant innate immunity, and revealed an intricate network of proteins involved in reactive oxygen species adaptation during Plants` Oxidative Burst response. We also identified proteins previously unknown to be involved in Xac-Citrus interaction, including the hypothetical protein XAC3981. A mutant strain for this gene has proved to be non-pathogenic in respect to classical symptoms of citrus canker induced in compatible plants.

CONCLUSIONS

This is the first time that a protein repertoire is shown to be active and working in an integrated manner during the infection process in a compatible host, pointing to an elaborate mechanism for adaptation of Xac once inside the plant.

Characterization of O-antigen polysaccharide backbone derived from nitric oxide-inducing Mesorhizobium loti MAFF 303099 lipopolysaccharide

Mesorhizobium loti is a member of rhizobia and establishes nitrogen-fixing symbioses with several Lotus species. Recently, we reported that M. loti MAFF 303099 bacterial cells and their lipopolysaccharide (LPS) preparations are involved in the beginning of the symbiotic process by inducing transient nitric oxide (NO) production in the roots of L. japonicus. We subsequently found that both the polysaccharide (PS) part and the lipid A moiety in LPS are responsible for the NO induction. In this study, we elucidated the chemical structure of M. loti O-polysaccharide (OPS) in PS. PS was prepared by mild acid hydrolysis of M. loti LPS followed by gel filtration chromatography. OPS was subjected to hydrazine treatment to obtain deacylated PS (dPS). Chemical composition analysis, ethylation analysis, and NMR spectra revealed the chemical structure of the M. loti OPS backbone in dPS to be →2)-α-l-6dTalp-(1 → 3)-α-l-6dTalp-(1 → 2)-α-l-Rhap-(1 → 2)-α-l-6dTalp-(1 → 3)-α-l-6dTalp-(1 → 3)-α-l-Rhap-(1→.

Immune resistance and tolerance strategies in malaria vector and non-vector mosquitoes

Background

The Anopheles gambiae complex consists of species that vary greatly in their capacity to transmit malaria. The mosquito immune system has been identified as a key factor that can influence whether Plasmodium infection establishes within the mosquito vector. This study was designed to investigate the immune responses of An. coluzzii, An. arabiensis and An. quadriannulatus mosquitoes. The first two mosquito species are major vectors of malaria in sub-Saharan Africa, while the third is thought to be a non-vector.

Methods

All three mosquito species were reared in mixed cultures. Their capacity to eliminate P. berghei and regulate midgut bacteria was examined.

Results

Our results revealed large differences in mosquito resistance to P. berghei. In all three mosquito species, immune reactions involving the complement system were triggered when the number of parasites that mosquitoes were challenged with exceeded a certain level, i.e. immune tolerance threshold. This threshold was markedly lower in An. quadriannulatus compared to An. coluzzii and An. arabiensis. We also demonstrated that the level of immune tolerance to P. berghei infection in the haemolymph is inversely correlated with the level of immune tolerance to microbiota observed in the midgut lumen after a blood meal. The malaria non-vector mosquito species, An. quadriannulatus was shown to have a much higher level of tolerance to microbiota in the midgut than An. coluzzii.

Conclusions

We propose a model whereby an increased tolerance to microbiota in the mosquito midgut results in lower tolerance to Plasmodium infection. In this model, malaria non-vector mosquito species are expected to have increased immune resistance in the haemocoel, possibly due to complement priming by microbiota elicitors. We propose that this strategy is employed by the malaria non-vector mosquito, An. quadriannulatus, while An. coluzzii has reduced tolerance to bacterial infection in the midgut and consequently reduced immune resistance to Plasmodium infection at the haemocoel level. An in-depth understanding of the molecular mechanisms regulating immune tolerance versus resistance in different mosquito vectors of malaria could guide the design of new vector and disease control strategies.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-017-2109-5) contains supplementary material, which is available to authorized users.

Rice Leaf Transcriptional Profiling Suggests a Functional Interplay Between Xanthomonas oryzae pv. oryzae Lipopolysaccharide and Extracellular Polysaccharide in Modulation of Defense Responses During Infection

Treatment of rice leaves with isolated Xanthomonas oryzae pv. oryzae lipopolysaccharide (LPS) induces the production of callose deposits, reactive oxygen species, and enhanced resistance against subsequent bacterial infection. Expression profiling of X. oryzae pv. oryzae LPS-treated rice (Oryza sativa subsp. indica) leaves showed that genes involved in the biosynthetic pathways for lignins, phenylpropanoids, chorismate, phenylalanine, salicylic acid, and ethylene, as well as a number of pathogenesis-related proteins are up-regulated. Gene ontology categories like cell-wall organization, defense response, stress response, and protein phosphorylation/kinases were found to be upregulated, while genes involved in photosynthesis were down-regulated. Coinfiltration with xanthan gum, the xanthomonas extracellular polysaccharide (EPS), suppressed LPS-induced callose deposition. Gene expression analysis of rice leaves that are treated with an EPS-deficient mutant of X. oryzae pv. oryzae indicated that a number of defense-regulated functions are up-regulated during infection. These transcriptional responses are attenuated in rice leaves treated with an EPS-deficient mutant that is also deficient in the O-antigen component of LPS. Overall, these results suggest that the O-antigen component of X. oryzae pv. oryzae LPS induces rice defense responses during infection and that these are suppressed by bacterial EPS.

Convergent evolution of filamentous microbes towards evasion of glycan-triggered immunity

896 I. 896 II. 896 III. 897 IV. 898 V. 899 VI. 899 900 References 900 SUMMARY: All filamentous microbes produce and release a wide range of glycans, which are essential determinants of microbe-microbe and microbe-host interactions. Major cell wall constituents, such as chitin and β-glucans, are elicitors of host immune responses. The widespread capacity for glycan perception in plants has driven the evolution of various strategies that help filamentous microbes to evade detection. Common strategies include structural and chemical modifications of cell wall components as well as the secretion of effector proteins that suppress chitin- and β-glucan-triggered immune responses. Thus, the necessity to avoid glycan-triggered immunity represents a driving force in the convergent evolution of filamentous microbes towards its suppression.

Determinación del contenido extra e intracelular de algunas enzimas líticas relacionadas con pared celular en raíces de clavel (Dianthus caryophyllus L.)

En el presente trabajo se verificó la presencia de algunas enzimas relacionadas con la pared celular vegetal (poligalacturonasa, pectato liasa, proteasa y xilanasa) en raíces de clavel (Dianthus caryophyllus L.). Así mismo, se determinaron los niveles de actividad de las mismas. Estos niveles se analizaron en diferentes espacios celulares: en el fluido intercelular que hace parte del apoplasto, en el simplasto y en el tejido total de las raíces de clavel (apoplasto y simplasto).Para extraer el fluido intercelular, se ensayaron dos metodologías. Para obtener el contenido intracelular (simplasto) y el extracto total (apoplasto y simplasto) en raíces de clavel se ensayaron tres metodologías que utilizaban como solución i) extractante buffer fosfato, ii) buffer fosfato con PVPP y iii) lavados con acetona a las raíces de clavel, antes de la extracción con buffer fosfatos. Los resultados mostraron el efecto de las diferentes soluciones en las actividades enzimáticas y en el contenido de proteína. Se propuso una de estas metodologías para extraer las cuatro enzimas en un único paso y realizar análisis comparativo de actividad enzimática.

Implementación y evaluación de una nariz electrónica para la detección de alcoholes lineales

Se desarrolló una nariz electrónica que permite la detección de alcoholes de manera sencilla y económica en comparación con las narices electrónicas tradicionales. Está basada en cuatro sensores de gas de SnO2 (dos comerciales y dos fabricados en el laboratorio), un sistema neumático irregular, un hardware y software para adquisición de datos y un software de reconocimiento de patrones. Se evaluó el comportamiento de la nariz y las condiciones de trabajo con muestras de vapor de alcoholes (metanol, etanol, n-butanol y 1-octanol) y se determinó que los alcoholes se pueden detectar con el arreglo de sensores preparado y pueden diferenciarse entre sí haciendo uso del análisis estadístico de componentes principales (PCA). El orden de detección encontrado para los alcoholes lineales fue el siguiente: metanol > etanol > n-butanol > 1-octanol. Se encontró también que haciendo uso del análisis de componentes principales (PCA) y realizando una normalización de los datos en el software de reconocimiento de patrones, la varianza total de las muestras también aumenta del 76% al 85%. Esto demuestra que una nariz simple y económica puede clasificar bien las muestras evaluadas.