Weeds Harbor an Impressive Diversity of Fungi, Which Offers Possibilities for Biocontrol.

The use of herbicides for weed control is very common, but some of them represent a threat to human health, are environmentally detrimental, and stimulate herbicide resistance. Therefore, using microorganisms as natural herbicides appears as a promising alternative. The mycoflorae colonizing different species of symptomatic and asymptomatic weeds were compared to characterize the possible mycoherbicidal candidates associated with symptomatic weeds. A collection of 475 symptomatic and asymptomatic plants belonging to 23 weed species was established. A metabarcoding approach based on amplification of the internal transcribed spacer (ITS) region combined with high-throughput amplicon sequencing revealed the diversity of fungal communities hosted by these weeds: 542 fungal genera were identified. The variability of the composition of fungal communities revealed a dispersed distribution of taxa governed neither by geographical location nor by the botanical species, suggesting a common core displaying nonspecific interactions with host plants. Beyond this core, specific taxa were more particularly associated with symptomatic plants. Some of these, such as Alternaria, Blumeria, Cercospora, Puccinia, are known pathogens, while others such as Sphaerellopsis, Vishniacozyma, and Filobasidium are not, at least on crops, and constitute new tracks to be followed in the search for mycoherbicidal candidates. IMPORTANCE This approach is original because the diversity of weed-colonizing fungi has rarely been studied before. Furthermore, targeting both the ITS1 and ITS2 regions to characterize the fungal communities (i) highlighted the complementarity of these two regions, (ii) revealed a great diversity of weed-colonizing fungi, and (iii) allowed for the identification of potential mycoherbicides, among which were unexpected genera.

Distinct genetic basis for root responses to lipo-chitooligosaccharide signal molecules from different microbial origins.

Lipo-chitooligosaccharides (LCOs) were originally found as symbiotic signals called Nod Factors (Nod-LCOs) controlling the nodulation of legumes by rhizobia. More recently, LCOs were also found in symbiotic fungi and, more surprisingly, very widely in the kingdom Fungi, including in saprophytic and pathogenic fungi. The LCO-V(C18:1, fucosylated/methyl fucosylated), hereafter called Fung-LCOs, are the LCO structures most commonly found in fungi. This raises the question of how legume plants such as Medicago truncatula can discriminate between Nod-LCOs and Fung-LCOs. To address this question, we performed a genome-wide association study on 173 natural accessions of M. truncatula, using a root branching phenotype and a newly developed local score approach. Both Nod-LCOs and Fung-LCOs stimulated root branching in most accessions, but the root responses to these two types of LCO molecules were not correlated. In addition, the heritability of the root response was higher for Nod-LCOs than for Fung-LCOs. We identified 123 loci for Nod-LCO and 71 for Fung-LCO responses, of which only one was common. This suggests that Nod-LCOs and Fung-LCOs both control root branching but use different molecular mechanisms. The tighter genetic constraint of the root response to Fung-LCOs possibly reflects the ancestral origin of the biological activity of these molecules.

Grapevine Stimulation: A Multidisciplinary Approach to Investigate the Effects of Biostimulants and a Plant Defense Stimulator.

The increasing use of plant defense stimulators (PDS) and biostimulants (BS) to make agriculture more sustainable has led to questions about their action on plants. A new PhysBioGen approach is proposed with complementary tools: PHYSiological (root weight); BIOchemical and BIOlogical (secondary metabolite quantification and Plasmopara viticola development) and expressions of 161 GENes involved in metabolic plant functions. The proposed approach investigated the effects of three phytostimulants on Vitis vinifera: one PDS (ASM) and one BS chelated (CH) and another enriched with seaweed (SW). Distinct responses were obtained between the PDS and the two BS. In particular, we observed the persistence of anti-mildew efficacy over time, correlated with differentiated expressions of defense genes (VvROMT, VvSAMT, VvPR8). As expected, the two BS displayed more similarities to each other than to the PDS (flavonols, anthocyanins, free salicylic acid). However, the two BS revealed differences in the modulation of genes involved in defense and primary metabolism and some genes were identified as potential markers of their action (VvWRKY1, VvLOX9, VvPOD, VvPDV1, VvXIP1, VVDnaJ). Our results highlight the common and the specific effects of the two BS and the PDS. These new tools could help in understanding the mode of action of phytostimulants in order to achieve better quality and production yield and/or as a way to limit chemical inputs in the vineyard.

MS-CleanR: A Feature-Filtering Workflow for Untargeted LC-MS Based Metabolomics.

Untargeted metabolomics using liquid chromatography-mass spectrometry (LC-MS) is currently the gold-standard technique to determine the full chemical diversity in biological samples. However, this approach still has many limitations; notably, the difficulty of accurately estimating the number of unique metabolites profiled among the thousands of MS ion signals arising from chromatograms. Here, we describe a new workflow, MS-CleanR, based on the MS-DIAL/MS-FINDER suite, which tackles feature degeneracy and improves annotation rates. We show that implementation of MS-CleanR reduces the number of signals by nearly 80% while retaining 95% of unique metabolite features. Moreover, the annotation results from MS-FINDER can be ranked according to the database chosen by the user, which enhance identification accuracy. Application of MS-CleanR to the analysis of Arabidopsis thaliana grown in three different conditions fostered class separation resulting from multivariate data analysis and led to annotation of 75% of the final features. The full workflow was applied to metabolomic profiles from three strains of the leguminous plant Medicago truncatula that have different susceptibilities to the oomycete pathogen Aphanomyces euteiches. A group of glycosylated triterpenoids overrepresented in resistant lines were identified as candidate compounds conferring pathogen resistance. MS-CleanR is implemented through a Shiny interface for intuitive use by end-users (available at https://github.com/eMetaboHUB/MS-CleanR).

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.

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.

Positive Gene Regulation by a Natural Protective miRNA Enables Arbuscular Mycorrhizal Symbiosis.

Arbuscular mycorrhizal (AM) symbiosis associates most plants with fungi of the phylum Glomeromycota. The fungus penetrates into roots and forms within cortical cell branched structures called arbuscules for nutrient exchange. We discovered that miR171b has a mismatched cleavage site and is unable to downregulate the miR171 family target gene, LOM1 (LOST MERISTEMS 1). This mismatched cleavage site is conserved among plants that establish AM symbiosis, but not in non-mycotrophic plants. Unlike other members of the miR171 family, miR171b stimulates AM symbiosis and is expressed specifically in root cells that contain arbuscules. MiR171b protects LOM1 from negative regulation by other miR171 family members. These findings uncover a unique mechanism of positive post-transcriptional regulation of gene expression by miRNAs and demonstrate its relevance for the establishment of AM symbiosis.

Anatomical features of skull base and oral cavity: a pilot study to determine the accessibility of the sella by transoral robotic-assisted surgery.

The role of transoral robotic surgery (TORS) in the skull base emerges and represents the natural progression toward miniinvasive resections in confined spaces. The accessibility of the sella via TORS has been recently described on fresh human cadavers. An anatomic study is mandatory to know if this approach would be feasible in the majority of patients regardless of their oral morphological features. From 30 skull base CT scans from patients who were asked to open their mouth as wide as they can, we measured specific dimensions of the oral cavity and the skull base, such as length of the palate, mouth opening and distance from the sella to the palate. All data were acquired on a sagittal midline plane and on a 25° rotation plane, which simulated the axis of the robotic instruments. Looking at the projection of the dental palatine line on the sella, we studied possible predictive factors of sellar accessibility and tried to bring objective data for surgical feasibility. We also proposed an angle α to study the working angle at the skull base. We observed that the maximal mouth opening was a good predictive factor of sellar accessibility by TORS (p < 0.05). The mouth aperture threshold value for a good sensitivity, over 80 %, was comparable to the mean value of mouth opening in our series, 38.9 and 39.4 mm respectively. Moreover, we showed a statistically significant increase of the working angle α at the skull base comparing the lateral access to the midline one (p < 0.05). This seemed to quantitatively demonstrate that the robotic arms placed at the labial commissure of the mouth can reach the sella. From these anatomical features and previous cadaveric dissections, we assume that TORS may be feasible on a majority of patients to remove pituitary adenomas.

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.

Strigolactones contribute to shoot elongation and to the formation of leaf margin serrations in Medicago truncatula R108.

Strigolactones were recently identified as a new class of plant hormones involved in the control of shoot branching. The characterization of strigolactone mutants in several species has progressively revealed their contribution to several other aspects of development in roots and shoots. In this article, we characterize strigolactone-deficient and strigolactone-insensitive mutants of the model legume Medicago truncatula for aerial developmental traits. The most striking mutant phenotype observed was compact shoot architecture. In contrast with what was reported in other species, this could not be attributed to enhanced shoot branching, but was instead due to reduced shoot elongation. Another notable feature was the modified leaf shape in strigolactone mutants: serrations at the leaf margin were smaller in the mutants than in wild-type plants. This phenotype could be rescued in a dose-dependent manner by exogenous strigolactone treatments of strigolactone-deficient mutants, but not of strigolactone-insensitive mutants. Treatment with the auxin transport inhibitor N-1-naphthylphtalamic acid resulted in smooth leaf margins, opposite to the effect of strigolactone treatment. The contribution of strigolactones to the formation of leaf serrations in M. truncatula R108 line represents a novel function of these hormones, which has not been revealed by the analysis of strigolactone mutants in other species.

High-density genome-wide association mapping implicates an F-box encoding gene in Medicago truncatula resistance to Aphanomyces euteiches.

• The use of quantitative disease resistance (QDR) is a promising strategy for promoting durable resistance to plant pathogens, but genes involved in QDR are largely unknown. To identify genetic components and accelerate improvement of QDR in legumes to the root pathogen Aphanomyces euteiches, we took advantage of both the recently generated massive genomic data for Medicago truncatula and natural variation of this model legume. • A high-density (≈5.1 million single nucleotide polymorphisms (SNPs)) genome-wide association study (GWAS) was performed with both in vitro and glasshouse phenotyping data collected for 179 lines. • GWAS identified several candidate genes and pinpointed two independent major loci on the top of chromosome 3 that were detected in both phenotyping methods. Candidate SNPs in the most significant locus (σ(A)²= 23%) were in the promoter and coding regions of an F-box protein coding gene. Subsequent qRT-PCR and bioinformatic analyses performed on 20 lines demonstrated that resistance is associated with mutations directly affecting the interaction domain of the F-box protein rather than gene expression. • These results refine the position of previously identified QTL to specific candidate genes, suggest potential molecular mechanisms, and identify new loci explaining QDR against A. euteiches.

Influence of High Shear Dispersion on the Production of Cellulose Nanofibers by Ultrasound-Assisted TEMPO-Oxidation of Kraft Pulp.

Cellulose nanofibers can be produced using a combination of TEMPO, sodium bromide (NaBr) and sodium hypochlorite, and mechanical dispersion. Recently, this process has been the subject of intensive investigation. However, studies on the aspects of mechanical treatment of this process remain marginal. The main objective of this study is to evaluate the high shear dispersion parameters (e.g., consistency, stator-rotor gap, recirculation rate and pH) and determine their influences on nanocellulose production using ultrasound-assisted TEMPO-oxidation of Kraft pulp. All nanofiber gels produced in this study exhibited rheological behaviors known as shear thinning. From all the dispersion parameters, the following conditions were identified as optimal: 0.042 mm stator-rotor gap, 200 mL/min recycle rate, dispersion pH of 7 and a feed consistency of 2%. High quality cellulose gel could be produced under these conditions. This finding is surely of great interest for the pulp and paper industry.

Fungal lipochitooligosaccharide symbiotic signals in arbuscular mycorrhiza.

Arbuscular mycorrhiza (AM) is a root endosymbiosis between plants and glomeromycete fungi. It is the most widespread terrestrial plant symbiosis, improving plant uptake of water and mineral nutrients. Yet, despite its crucial role in land ecosystems, molecular mechanisms leading to its formation are just beginning to be unravelled. Recent evidence suggests that AM fungi produce diffusible symbiotic signals. Here we show that Glomus intraradices secretes symbiotic signals that are a mixture of sulphated and non-sulphated simple lipochitooligosaccharides (LCOs), which stimulate formation of AM in plant species of diverse families (Fabaceae, Asteraceae and Umbelliferae). In the legume Medicago truncatula these signals stimulate root growth and branching by the symbiotic DMI signalling pathway. These findings provide a better understanding of the evolution of signalling mechanisms involved in plant root endosymbioses and will greatly facilitate their molecular dissection. They also open the way to using these natural and very active molecules in agriculture.

Negative regulation of meiotic gene expression by the nuclear poly(a)-binding protein in fission yeast.

Meiosis is a cellular differentiation process in which hundreds of genes are temporally induced. Because the expression of meiotic genes during mitosis is detrimental to proliferation, meiotic genes must be negatively regulated in the mitotic cell cycle. Yet, little is known about mechanisms used by mitotic cells to repress meiosis-specific genes. Here we show that the poly(A)-binding protein Pab2, the fission yeast homolog of mammalian PABPN1, controls the expression of several meiotic transcripts during mitotic division. Our results from chromatin immunoprecipitation and promoter-swapping experiments indicate that Pab2 controls meiotic genes post-transcriptionally. Consistently, we show that the nuclear exosome complex cooperates with Pab2 in the negative regulation of meiotic genes. We also found that Pab2 plays a role in the RNA decay pathway orchestrated by Mmi1, a previously described factor that functions in the post-transcriptional elimination of meiotic transcripts. Our results support a model in which Mmi1 selectively targets meiotic transcripts for degradation via Pab2 and the exosome. Our findings have therefore uncovered a mode of gene regulation whereby a poly(A)-binding protein promotes RNA degradation in the nucleus to prevent untimely expression.

Crossing the borders: poly(A)-binding proteins working on both sides of the fence.

The addition of a 3' poly(A) tail is a pre-requisite for the maturation of the majority of eukaryotic transcripts. In most eukaryotic species, RNA poly(A) tails are bound by two important poly(A)-binding proteins (PABPs): PABPC1 and PABPN1 that localize to the cytoplasm and the nucleus, respectively. Such steady state localization for PABPN1 and PABPC1 led to a model whereby PABPN1-bound nuclear mRNAs are remodeled during or after nuclear export so that PABPN1 is replaced by PABPC1 to allow robust cap-dependent translation in the cytoplasm. Here we discuss evidence that challenge the view in which PABPN1 and PABPC1 function solely in the nucleus and cytoplasm, respectively. We discuss accumulating evidence that support nuclear roles for PABPC1 in mRNA biogenesis as well as cytoplasmic roles for PABPN1 in translational control. Because 3' poly(A) tails can also act as a degradation mark via the exosome complex of 3'-5' exonucleases, we also discuss recent results that involve the nuclear PABP in posttranscriptional gene regulation.