The mycoparasite Pythium oligandrum induces legume pathogen resistance and shapes rhizosphere microbiota without impacting mutualistic interactions

Pythium oligandrum is a soil-borne oomycete associated with rhizosphere and root tissues. Its ability to enhance plant growth, stimulate plant immunity and parasitize fungal and oomycete preys has led to the development of agricultural biocontrol products. Meanwhile, the effect of P. oligandrum on mutualistic interactions and more generally on root microbial communities has not been investigated. Here, we developed a biological system comprising P. oligandrum interacting with two legume plants, Medicago truncatula and Pisum sativum. P. oligandrum activity was investigated at the transcriptomics level through an RNAseq approach, metabolomics and finally metagenomics to investigate the impact of P. oligandrum on root microbiota. We found that P. oligandrum promotes plant growth in these two species and protects them against infection by the oomycete Aphanomyces euteiches, a devastating legume root pathogen. In addition, P. oligandrum up-regulated more than 1000 genes in M. truncatula roots including genes involved in plant defense and notably in the biosynthesis of antimicrobial compounds and validated the enhanced production of M. truncatula phytoalexins, medicarpin and formononetin. Despite this activation of plant immunity, we found that root colonization by P. oligandrum did not impaired symbiotic interactions, promoting the formation of large and multilobed symbiotic nodules with Ensifer meliloti and did not negatively affect the formation of arbuscular mycorrhizal symbiosis. Finally, metagenomic analyses showed the oomycete modifies the composition of fungal and bacterial communities. Together, our results provide novel insights regarding the involvement of P. oligandrum in the functioning of plant root microbiota.

Temporal, age and geographical variation in vaccine efficacy against infection by the Delta and Omicron variants in the community in France, December 2021 to March 2022

OBJECTIVES

Quantify how the vaccine efficacy of BNT162b2, mRNA-1273, AD26.COV2-S, ChAdOx1 nCoV-19 against detected infection by the SARS-CoV-2 Delta and Omicron variants varied by time since last dose, vaccine scheme, age and geographic areas.

METHODS

We analyzed 3,261,749 community PCR tests conducted by private laboratories in France in December 2021 to March 2022 with a test-negative design comparing vaccinated to unvaccinated individuals.

RESULTS

Efficacy against detected infection by Delta was 89% [95% CI, 86 - 91%] at two weeks down to 59% [56-61%] at 26 weeks and more after the second dose. Efficacy against Omicron was 48% [45-51%] at two weeks, down to 4% [2-5%] at 16 weeks after the second dose. A third dose temporarily restored efficacy. Efficacy against Omicron was lower in children and the elderly. Geographical variability in efficacy may reflect variability in the ratio of number of contacts of vaccinated vs. unvaccinated individuals. This ratio ranged from 0 to +50% across departments, and correlated with the number of restaurants and bars per inhabitants (beta = 15.0 [0.75 - 29], p-value = 0.04), places that only vaccinated individuals could access in the study period.

CONCLUSION

SARS-CoV-2 vaccines conferred low and transient protection against Omicron infection.

Developmental Modulation of Root Cell Wall Architecture Confers Resistance to an Oomycete Pathogen

The cell wall is the primary interface between plant cells and their immediate environment and must balance multiple functionalities, including the regulation of growth, the entry of beneficial microbes, and protection against pathogens. Here, we demonstrate how API, a SCAR2 protein component of the SCAR/WAVE complex, controls the root cell wall architecture important for pathogenic oomycete and symbiotic bacterial interactions in legumes. A mutation in API results in root resistance to the pathogen Phytophthora palmivora and colonization defects by symbiotic rhizobia. Although api mutant plants do not exhibit significant overall growth and development defects, their root cells display delayed actin and endomembrane trafficking dynamics and selectively secrete less of the cell wall polysaccharide xyloglucan. Changes associated with a loss of API establish a cell wall architecture with altered biochemical properties that hinder P. palmivora infection progress. Thus, developmental stage-dependent modifications of the cell wall, driven by SCAR/WAVE, are important in balancing cell wall developmental functions and microbial invasion.

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The SCAR protein API controls actin and endomembrane trafficking dynamics

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SCAR proteins of several plant species can support symbiosis and pathogen infection

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A mutation in API affects specific biochemical properties of plant cell walls

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An altered wall architecture results in root resistance to Phytophthora palmivora

Phyllosphere Colonization by a Soil Streptomyces sp. Promotes Plant Defense Responses Against Fungal Infection

Streptomycetes are soil-dwelling, filamentous actinobacteria and represent a prominent bacterial clade inside the plant root microbiota. The ability of streptomycetes to produce a broad spectrum of antifungal metabolites suggests that these bacteria could be used to manage plant diseases. Here, we describe the identification of a soil Streptomyces strain named AgN23 which strongly activates a large array of defense responses when applied on Arabidopsis thaliana leaves. AgN23 increased the biosynthesis of salicylic acid, leading to the development of salicylic acid induction deficient 2 (SID2)-dependent necrotic lesions. Size exclusion fractionation of plant elicitors secreted by AgN23 showed that these signals are tethered into high molecular weight complexes. AgN23 mycelium was able to colonize the leaf surface, leading to plant resistance against Alternaria brassicicola infection in wild-type Arabidopsis plants. AgN23-induced resistance was found partially compromised in salicylate, jasmonate, and ethylene mutants. Our data show that Streptomyces soil bacteria can develop at the surface of plant leaves to induce defense responses and protection against foliar fungal pathogens, extending their potential use to manage plant diseases.

Lipo-chitooligosaccharide signalling blocks a rapid pathogen-induced ROS burst without impeding immunity

Molecular signals released by microbes at the surface of plant roots and leaves largely determine host responses, notably by triggering either immunity or symbiosis. How these signalling pathways cross-talk upon coincident perception of pathogens and symbionts is poorly described in plants forming symbiosis. Nitrogen fixing symbiotic Rhizobia spp. and arbuscular mycorrhizal fungi produce lipo-chitooligosaccharides (LCOs) to initiate host symbiotic programmes. In Medicago truncatula roots, the perception of LCOs leads to reduced efflux of reactive oxygen species (ROS). By contrast, pathogen perception generally triggers a strong ROS burst and activates defence gene expression. Here we show that incubation of M. truncatula seedlings with culture filtrate (CF) of the legume pathogen Aphanomyces euteiches alone or simultaneously with Sinorhizobium meliloti LCOs, resulted in a strong ROS release. However, this response was completely inhibited if CF was added after pre-incubation of seedlings with LCOs. By contrast, expression of immunity-associated genes in response to CF and disease resistance to A. euteiches remained unaffected by LCO treatment of M. truncatula roots. Our findings suggest that symbiotic plants evolved ROS inhibition response to LCOs to facilitate early steps of symbiosis whilst maintaining a parallel defence mechanisms toward pathogens.

Symbiosis genes for immunity and vice versa

Basic molecular knowledge on plant-pathogen interactions has largely been gained from reverse and forward genetics in Arabidopsis thaliana. However, as this model plant is unable to establish endosymbiosis with mycorrhizal fungi or rhizobia, plant responses to mutualistic symbionts have been studied in parallel in other plant species, mainly legumes. The resulting analyses led to the identification of gene networks involved in various functions, from microbe recognition to signalling and plant responses, thereafter assigned to either mutualistic symbiosis or immunity, according to the nature of the initially inoculated microbe. The increasing development of new pathosystems and genetic resources in model legumes and the implementation of reverse genetics in plants such as rice and tomato that interact with both mycorrhizal fungi and pathogens, have highlighted the dual role of plant genes previously thought to be specific to mutualistic or pathogenic interactions. The next challenges will be to determine whether such genes have similar functions in both types of interaction and if not, whether the perception of microbial compounds or the involvement of specific plant signalling components is responsible for the appropriate plant responses to the encountered microorganisms.

The Medicago truncatula GRAS protein RAD1 supports arbuscular mycorrhiza symbiosis and Phytophthora palmivora susceptibility

The roots of most land plants are colonized by symbiotic arbuscular mycorrhiza (AM) fungi. To facilitate this symbiosis, plant genomes encode a set of genes required for microbial perception and accommodation. However, the extent to which infection by filamentous root pathogens also relies on some of these genes remains an open question. Here, we used genome-wide association mapping to identify genes contributing to colonization of Medicago truncatula roots by the pathogenic oomycete Phytophthora palmivora. Single-nucleotide polymorphism (SNP) markers most significantly associated with plant colonization response were identified upstream of RAD1, which encodes a GRAS transcription regulator first negatively implicated in root nodule symbiosis and recently identified as a positive regulator of AM symbiosis. RAD1 transcript levels are up-regulated both in response to AM fungus and, to a lower extent, in infected tissues by P. palmivora where its expression is restricted to root cortex cells proximal to pathogen hyphae. Reverse genetics showed that reduction of RAD1 transcript levels as well as a rad1 mutant are impaired in their full colonization by AM fungi as well as by P. palmivora. Thus, the importance of RAD1 extends beyond symbiotic interactions, suggesting a general involvement in M. truncatula microbe-induced root development and interactions with unrelated beneficial and detrimental filamentous microbes.

Plenty Is No Plague: Streptomyces Symbiosis with Crops

Streptomyces spp. constitute a major clade of the phylum Actinobacteria. These Gram-positive, filamentous prokaryotes are ubiquitous in soils and marine sediments, and are commonly found in the rhizosphere or inside plant roots. Plant-interacting Streptomyces have received limited attention, in contrast to Streptomyces spp. extensively investigated for decades in medicine given their rich potential for secondary metabolite biosynthesis. Recent genomic, metabolomic, and biotechnological advances have produced key insights into Streptomyces spp., paving the way to the use of their metabolites in agriculture. In this Opinion article we propose how Streptomyces spp. could dominate future aspects of crop nutrition and protection. Risks and benefits of the use of these microorganisms in agriculture are also discussed.

MtNF-YA1, A Central Transcriptional Regulator of Symbiotic Nodule Development, Is Also a Determinant of Medicago truncatula Susceptibility toward a Root Pathogen

Plant NF-Y transcription factors control a wide array of biological functions enabling appropriate reproductive and developmental processes as well as adaptation to various abiotic and biotic environments. In Medicago truncatula, MtNF-YA1 was previously identified as a key determinant for nodule development and establishment of rhizobial symbiosis. Here, we highlight a new role for this protein in compatibility to Aphanomyces euteiches, a root pathogenic oomycete. The Mtnf-ya1-1 mutant plants showed better survival rate, reduced symptoms, and increased development of their root apparatus as compared to their wild-type (WT) background A17. MtNF-YA-1 was specifically up-regulated by A. euteiches in F83005.5, a highly susceptible natural accession of M. truncatula while transcript level remained stable in A17, which is partially resistant. The role of MtNF-YA1 in F83005.5 susceptibility was further documented by reducing MtNF-YA1 expression either by overexpression of the miR169q, a microRNA targeting MtNF-YA1, or by RNAi approaches leading to a strong enhancement in the resistance of this susceptible line. Comparative analysis of the transcriptome of WT and Mtnf-ya1-1 led to the identification of 1509 differentially expressed genes. Among those, almost 36 defense-related genes were constitutively expressed in Mtnf-ya1-1, while 20 genes linked to hormonal pathways were repressed. In summary, we revealed an unexpected dual role for this symbiotic transcription factor as a key player in the compatibility mechanisms to a pathogen.

Modulation of host cell biology by plant pathogenic microbes

Plant-pathogen interactions can result in dramatic visual changes in the host, such as galls, phyllody, pseudoflowers, and altered root-system architecture, indicating that the invading microbe has perturbed normal plant growth and development. These effects occur on a cellular level but range up to the organ scale, and they commonly involve attenuation of hormone homeostasis and deployment of effector proteins with varying activities to modify host cell processes. This review focuses on the cellular-reprogramming mechanisms of filamentous and bacterial plant pathogens that exhibit a biotrophic lifestyle for part, if not all, of their lifecycle in association with the host. We also highlight strategies for exploiting our growing knowledge of microbial host reprogramming to study plant processes other than immunity and to explore alternative strategies for durable plant resistance.

The CRE1 cytokinin pathway is differentially recruited depending on Medicago truncatula root environments and negatively regulates resistance to a pathogen

Cytokinins are phytohormones that regulate many developmental and environmental responses. The Medicago truncatula cytokinin receptor MtCRE1 (Cytokinin Response 1) is required for the nitrogen-fixing symbiosis with rhizobia. As several cytokinin signaling genes are modulated in roots depending on different biotic and abiotic conditions, we assessed potential involvement of this pathway in various root environmental responses. Phenotyping of cre1 mutant roots infected by the Gigaspora margarita arbuscular mycorrhizal (AM) symbiotic fungus, the Aphanomyces euteiches root oomycete, or subjected to an abiotic stress (salt), were carried out. Detailed histological analysis and quantification of cre1 mycorrhized roots did not reveal any detrimental phenotype, suggesting that MtCRE1 does not belong to the ancestral common symbiotic pathway shared by rhizobial and AM symbioses. cre1 mutants formed an increased number of emerged lateral roots compared to wild-type plants, a phenotype which was also observed under non-stressed conditions. In response to A. euteiches, cre1 mutants showed reduced disease symptoms and an increased plant survival rate, correlated to an enhanced formation of lateral roots, a feature previously linked to Aphanomyces resistance. Overall, we showed that the cytokinin CRE1 pathway is not only required for symbiotic nodule organogenesis but also affects both root development and resistance to abiotic and biotic environmental stresses.

An original architectured NiTi silicone rubber structure for biomedical applications

This paper deals with composite structures for biomedical applications. For this purpose, an architectured tubular structure composed of Nickel Titanium (NiTi) Shape Memory Alloy (SMA) and silicone rubber was fabricated. One of the main interests of such structures is to ensure a good adhesion between its two constitutive materials. A previous study of the authors (Rey et al., 2014) has shown that the adhesion between NiTi and silicone rubber can be improved by an adhesion promoter or plasma treatment. However, adhesion promoters are often not biocompatible. Hence, plasma treatment is favored to be used in the present study. Three different gases were tested; air, argon and oxygen. The effects of these treatments on the maximum force required to pull-out a NiTi wire from the silicone rubber matrix were investigated by means of pull-out tests carried out with a self-developed device. Among the three gases, a higher maximum force was obtained for argon gas in the plasma treatment. A tube shaped architectured NiTi/silicone rubber structure was then produced using this treatment. The composite was tested by means of a bulge test. Results open a new way of investigations for architectured NiTi-silicone structures for biomechanical applications.

Cross-interference of plant development and plant-microbe interactions

Plant roots are host to a multitude of filamentous microorganisms. Among these, arbuscular mycorrhizal fungi provide benefits to plants, while pathogens trigger diseases resulting in significant crop yield losses. It is therefore imperative to study processes which allow plants to discriminate detrimental and beneficial interactions in order to protect crops from diseases while retaining the ability for sustainable bio-fertilisation strategies. Accumulating evidence suggests that some symbiosis processes also affect plant-pathogen interactions. A large part of this overlap likely constitutes plant developmental processes. Moreover, microbes utilise effector proteins to interfere with plant development. Here we list relevant recent findings on how plant-microbe interactions intersect with plant development and highlight future research leads.

Interactions of beneficial and detrimental root-colonizing filamentous microbes with plant hosts

Understanding commonalities and differences of how symbiotic and parasitic microbes interact with plants will improve advantageous interactions and allow pathogen control strategies in crops. Recently established systems enable studies of root pathogenic and symbiotic interactions in the same plant species.

[Usefulness of haemoperfusion in the treatment of the severe septic patient: an update]

Haemoperfusion is an extracorporeal technique that removes endotoxin and/or inflammatory mediators by means of an adsorptive mechanism during the passage of the blood through a porous filter. Most of the studies in the literature use polymyxin B as the adsorptive agent. This treatment is based on the assumption that the removal of endotoxin and inflammatory mediators from the circulation attenuates the inflammatory response in sepsis. This review summarizes the theoretical basis, and the experimental and clinical results published to date with the use of haemoperfusion. Although most of the studies show positive results, some doubts have arisen about the suitability of the methods described (small number of cases, low quality of the experimental design, and excessive mortality in the control groups). There are also some inconsistencies regarding the theoretical basis of its use (lack of positive effects after the removal of endotoxin from the circulation using alternative mechanisms, discrepancies regarding the best moment to initiate the therapy, unexplained beneficial effects in the absence of increased endotoxin levels). It is the opinion of the authors that haemoperfusion represents a promising therapy for the treatment of sepsis, but consider that its usefulness requires confirmation in well designed studies before being included in protocols.

NFP, a LysM protein controlling Nod factor perception, also intervenes in Medicago truncatula resistance to pathogens

Plant LysM proteins control the perception of microbial-derived N-acetylglucosamine compounds for the establishment of symbiosis or activation of plant immunity. This raises questions about how plants, and notably legumes, can differentiate friends and foes using similar molecular actors and whether any receptors can intervene in both symbiosis and resistance. To study this question, nfp and lyk3 LysM-receptor like kinase mutants of Medicago truncatula that are affected in the early steps of nodulation, were analysed following inoculation with Aphanomyces euteiches, a root oomycete. The role of NFP in this interaction was further analysed by overexpression of NFP and by transcriptome analyses. nfp, but not lyk3, mutants were significantly more susceptible than wildtype plants to A. euteiches, whereas NFP overexpression increased resistance. Transcriptome analyses on A. euteiches inoculation showed that mutation in the NFP gene led to significant changes in the expression of c. 500 genes, notably involved in cell dynamic processes previously associated with resistance to pathogen penetration. nfp mutants also showed an increased susceptibility to the fungus Colletotrichum trifolii. These results demonstrate that NFP intervenes in M. truncatula immunity, suggesting an unsuspected role for NFP in the perception of pathogenic signals.

An experimental system to study responses of Medicago truncatula roots to chitin oligomers of high degree of polymerization and other microbial elicitors

A fully acetylated, soluble CO preparation of mean DP of ca. 7 was perceived with high sensitivity by M. truncatula in a newly designed versatile root elicitation assay. The root system of legume plants interacts with a large variety of microorganisms, either pathogenic or symbiotic. Understanding how legumes recognize and respond specifically to pathogen-associated or symbiotic signals requires the development of standardized bioassays using well-defined preparations of the corresponding signals. Here we describe the preparation of chitin oligosaccharide (CO) fractions from commercial chitin and their characterization by a combination of liquid-state and solid-state nuclear magnetic resonance spectroscopy. We show that the CO fraction with highest degree of polymerization (DP) became essentially insoluble after lyophilization. However, a fully soluble, fully acetylated fraction with a mean DP of ca. 7 was recovered and validated by showing its CERK1-dependent activity in Arabidopsis thaliana. In parallel, we developed a versatile root elicitation bioassay in the model legume Medicago truncatula, using a hydroponic culture system and the Phytophthora β-glucan elicitor as a control elicitor. We then showed that M. truncatula responded with high sensitivity to the CO elicitor, which caused the production of extracellular reactive oxygen species and the transient induction of a variety of defense-associated genes. In addition, the bioassay allowed detection of elicitor activity in culture filtrates of the oomycete Aphanomyces euteiches, opening the way to the analysis of recognition of this important legume root pathogen by M. truncatula.

Short-chain chitin oligomers from arbuscular mycorrhizal fungi trigger nuclear Ca2+ spiking in Medicago truncatula roots and their production is enhanced by strigolactone

The primary objective of this study was to identify the molecular signals present in arbuscular mycorrhizal (AM) germinated spore exudates (GSEs) responsible for activating nuclear Ca(2+) spiking in the Medicago truncatula root epidermis. Medicago truncatula root organ cultures (ROCs) expressing a nuclear-localized cameleon reporter were used as a bioassay to detect AM-associated Ca(2+) spiking responses and LC-MS to characterize targeted molecules in GSEs. This approach has revealed that short-chain chitin oligomers (COs) can mimic AM GSE-elicited Ca(2+) spiking, with maximum activity observed for CO4 and CO5. This spiking response is dependent on genes of the common SYM signalling pathway (DMI1/DMI2) but not on NFP, the putative Sinorhizobium meliloti Nod factor receptor. A major increase in the CO4/5 concentration in fungal exudates is observed when Rhizophagus irregularis spores are germinated in the presence of the synthetic strigolactone analogue GR24. By comparison with COs, both sulphated and nonsulphated Myc lipochito-oligosaccharides (LCOs) are less efficient elicitors of Ca(2+) spiking in M. truncatula ROCs. We propose that short-chain COs secreted by AM fungi are part of a molecular exchange with the host plant and that their perception in the epidermis leads to the activation of a SYM-dependent signalling pathway involved in the initial stages of fungal root colonization.

Less postoperative nausea and vomiting after propofol + remifentanil versus propofol + fentanyl anaesthesia during plastic surgery

BACKGROUND

The effect of different opioids on postoperative nausea and vomiting (PONV) has not been conclusively determined yet, thus the aim of this study was to compare the incidence of PONV in propofol-anaesthetized patients receiving either fentanyl or remifentanil as opioid supplement.

METHODS

Sixty ASA physical status I and II patients scheduled for plastic surgery gave their written informed consent for this prospective, randomized, double-blind study. Anaesthesia was induced with propofol, rocuronium and fentanyl (n = 30; 2 microg kg(-1)) or remifentanil (n = 30; 1 microg kg(-1)). After tracheal intubation, anaesthesia was maintained with propofol, oxygen in air and an infusion of the opioid studied, which was modified according to clinical criteria. Baseline postoperative analgesia was achieved with intravenous propacetamol + metamizol. Intravenous morphine was given if visual analogic scale (VAS) for pain was > or = 4 (scale 0-10) and metoclopramide was administered if a patient presented > or = 2 PONV episodes (nausea or vomiting) in less than 30 min. Postoperatively (2, 12 and 24 h), we registered VAS, rescue morphine consumption, number of patients with episodes of PONV and number of patients requiring metoclopramide. P < 0.05 was considered significant.

RESULTS

There were no significant differences between groups in the demographic parameters, ASA physical status, propofol dose, VAS, and rescue morphine requirements. Fourteen patients in the fentanyl group and four in the remifentanil group presented PONV episodes 2-12 h postoperative hours' interval; (P < 0.05). Ten patients in the fentanyl group and four in the remifentanil group presented vomiting episodes in the same period (P < 0.05); and eight patients in the fentanyl group and one in the remifentanil group required metoclopramide; (P < 0.05). The number of postoperative PONV episodes were low, both in the 0-2-h period (n = 2 vs. n = 1, fentanyl and remifentanil, respectively) and in the 12-24-h period (n = 3 vs. n = 1).

CONCLUSION

Propofol + fentanyl anaesthesia resulted in a higher incidence of PONV and requirements of antiemetic drugs in the period between 2 and 12 postoperative hours compared with propofol + remifentanil, in patients undergoing plastic surgery.