Perception et transduction du signal bactérien facteur Nod dans l'établissement de la symbiose rhizobium-légumineuse : recherche et caractérisation de partenaires du LysM-RLK LYK3, un récepteur putatif des facteurs Nod chez Medicago truncatula

Les légumineuses sont capables d'établir une interaction symbiotique avec des bactéries du sol, collectivement appelées rhizobia. Les facteurs Nod (NFs), molécules produites par le symbiote, sont indispensables à l'établissement de cette symbiose. Les études génétiques chez M. truncatula ont révélé l'implication de deux récepteurs kinase de la famille des LysM-RLKs, NFP et LYK3, dans la perception des NFs. NFP est indispensable à toutes les réponses induites chez l'hôte par les NFs alors que LYK3 contrôle spécifiquement l'infection. Afin de mieux comprendre les mécanismes de signalisation encore mal connus en aval de LYK3, deux criblages de banques d'ADNc de M. truncatula dans deux systèmes double-hybride ont été entrepris dans le but d'identifier des partenaires de ce récepteur. Un de ces criblages a permis l'identification d'un gène codant pour une E3 ubiquitine ligase de la famille des U-Box et nommé MtPUB1. MtPUB1 joue un rôle négatif dans les processus d'infection et de nodulation. Comme pour LYK3, ce rôle dépend de la nature des NFs produits par le symbiote. En parallèle, il a été montré par une approche ciblée que LYK3, NFP et DMI2 peuvent interagir avec une remorine, protéine membranaire contrôlant positivement l'infection chez M. truncatula.Leguminous plants can establish symbiotic interaction with nitrogen fixing soil-born bacteria collectively referred as rhizobia. Nod factors (NFs) are rhizobia produced molecules essential to the establishment of this interaction. Genetic studies of the NFs perception in M. truncatula led to the identification of two LysM receptor-like kinases, NFP and LYK3. NFP is necessary for all NFs induced responses while LYK3 specifically controls infection. Signalling events downstream LYK3 are poorly understood. To decipher this signalling pathway, two different yeast two-hybrid screens using M. truncatula cDNAs and LYK3 kinase as bait were performed. One screen identified an E3 ubiquitin ligase of the U-Box family renamed MtPUB1. MtPUB1 plays a negative role in infection and nodulation, and as for LYK3, this role relies on the NFs structure produced by the rhizobia. In parallel, a second approach based on pairwise interaction assays identified a remorin protein as partner of all three symbiotic receptor-like kinases, NFP, LYK3 and DMI2

The family of Peps and their precursors in Arabidopsis: differential expression and localization but similar induction of pattern-triggered immune responses

In Arabidopsis thaliana, the endogenous danger peptides, AtPeps, have been associated with plant defences reminiscent of those induced in pattern-triggered immunity. AtPeps are perceived by two homologous receptor kinases, PEPR1 and PEPR2, and are encoded in the C termini of the PROPEP precursors. Here, we report that, contrary to the seemingly redundant AtPeps, the PROPEPs fall at least into two distinct groups. As revealed by promoter-β-glucuronidase studies, expression patterns of PROPEP1-3, -5, and -8 partially overlapped and correlated with those of the PEPR1 and -2 receptors, whereas those of PROPEP4 and -7 did not share any similarities with the former. Moreover, bi-clustering analysis indicated an association of PROPEP1, -2, and -3 with plant defence, whereas PROPEP5 expression was related to patterns of plant reproduction. In addition, at the protein level, PROPEPs appeared to be distinct. PROPEP3::YFP (fused to yellow fluorescent protein) was present in the cytosol, but, in contrast to previous predictions, PROPEP1::YFP and PROPEP6::YFP localized to the tonoplast. Together with the expression patterns, this could point to potentially non-redundant roles among the members of the PROPEP family. By contrast, their derived AtPeps, including the newly reported AtPep8, when applied exogenously, provoked activation of defence-related responses in a similar manner, suggesting a high level of functional redundancy between the AtPeps. Taken together, our findings reveal an apparent antagonism between AtPep redundancy and PROPEP variability, and indicate new roles for PROPEPs besides plant immunit

Attenuation of pattern recognition receptor signaling is mediated by a MAP kinase kinase kinase

Pattern recognition receptors (PRRs) play a key role in plant and animal innate immunity. PRR binding of their cognate ligand triggers a signaling network and activates an immune response. Activation of PRR signaling must be controlled prior to ligand binding to prevent spurious signaling and immune activation. Flagellin perception in Arabidopsis through FLAGELLIN‐SENSITIVE 2 (FLS2) induces the activation of mitogen‐activated protein kinases (MAPKs) and immunity. However, the precise molecular mechanism that connects activated FLS2 to downstream MAPK cascades remains unknown. Here, we report the identification of a differentially phosphorylated MAP kinase kinase kinase that also interacts with FLS2. Using targeted proteomics and functional analysis, we show that MKKK7 negatively regulates flagellin‐triggered signaling and basal immunity and this requires phosphorylation of MKKK7 on specific serine residues. MKKK7 attenuates MPK6 activity and defense gene expression. Moreover, MKKK7 suppresses the reactive oxygen species burst downstream of FLS2, suggesting that MKKK7‐mediated attenuation of FLS2 signaling occurs through direct modulation of the FLS2 complex

A METAGENOMIC ASSESSMENT OF BACTERIAL CONTAMINATION OF DUST EVENTS IN SENEGAL

Previous work in the Caribbean and West Africa have shown that air samples taken during dust events contain microorganisms (bacteria, fungi, viruses), including human pathogens that can cause many respiratory diseases. To better understand the potential downstream effect of bacteria dust on human health and public ecosystems, it is important to characterize the source population. In this study, we aimed to explore the bacterial populations of African dust samples collected between 2013-2017. The dust samples were collected using the spatula method, then the hypervariable regions (V3 and V4) of the 16S rRNA gene were amplified using PCR followed byMiSeq Illumina sequencing. Analysis of the sequencing data were performed using MG-RAST. At the phylum level, the proportions of Actinobacteria (22%), Firmicutes (20%), Proteobacteria (19%), and Bacteroidetes (13%) were respectively predominant in all dust samples. At the genus level, Bacillus(16%), Pseudomonas(10%), Nocardiodes and Exiguobacterium (5%) are the most dominated genera in African dust samples collected in this study.The study showed that molecular characterization of dust microbial population remains a very efficient method, also applicable to the search for viruses and fungi in this type of sample. It is important to note that the majority of microorganisms identified in this study can cause respiratory diseases.</jats:p

The leucine-rich repeat receptor kinase QSK1 is a novel regulator of PRR-RBOHD complex and is employed by the bacterial effector HopF2Pto_{Pto} to modulate plant immunity

Plants detect pathogens using cell-surface pattern recognition receptors (PRRs) like EFR and FLS2, which recognize bacterial EF-Tu and flagellin, respectively. These PRRs, belonging to the leucine-rich repeat receptor kinase (LRR-RK) family, activate the production of reactive oxygen species via the NADPH oxidase RBOHD. The PRR-RBOHD complex is tightly regulated to prevent unwarranted or exaggerated immune responses. However, certain pathogenic effectors can subvert these regulatory mechanisms, thereby suppressing plant immunity. To elucidate the intricate dynamics of the PRR-RBOHD complex, we conducted a comparative co-immunoprecipitation analysis using EFR, FLS2, and RBOHD. We identified QSK1, an LRR-RK, as a novel component of the PRR-RBOHD complex. QSK1 functions as a negative regulator of PRR-triggered immunity (PTI) by downregulating the abundance of FLS2 and EFR. QSK1 is targeted by the bacterial effector HopF2$_{Pto}$, a mono-ADP ribosyltransferase, resulting in the reduction of FLS2 and EFR levels through both transcriptional and transcription-independent pathways, thereby inhibiting PTI. Furthermore, HopF2$_{Pto}$ reduces transcript levels of PROSCOOP genes encoding important stress-regulated phytocytokines and their receptor MIK2. Importantly, HopF2Pto requires QSK1 for its accumulation and virulence functions within plants. In summary, our results provide novel insights into the mechanism by which HopF2$_{Pto}$ employs QSK1 to desensitize plants to pathogen attack. One Sentence Summary: QSK1, a novel component in the plant immune receptor complex, downregulates these receptors and phytocytokines, and is exploited by bacterial effector HopF2$_{Pto}$ to desensitize plants to pathogen attack

Contamination microbienne des eaux du cours d’eau de Bise (Haute-Savoie) et modélisation des écoulements

Diplôme : Maste

Perception et transduction du signal bactérien facteur Nod dans l'établissement de la symbiose rhizobium-légumineuse (recherche et caractérisation de partenaires du LysM-RLK LYK3, un récepteur putatif des facteurs Nod chez Medicago truncatula)

TOULOUSE3-BU Sciences (315552104) / SudocSudocFranceF

Calcium Signalling in Plant Biotic Interactions

Calcium (Ca2+) is a universal second messenger involved in various cellular processes, leading to plant development and to biotic and abiotic stress responses. Intracellular variation in free Ca2+ concentration is among the earliest events following the plant perception of environmental change. These Ca2+ variations differ in their spatio-temporal properties according to the nature, strength and duration of the stimulus. However, their conversion into biological responses requires Ca2+ sensors for decoding and relaying. The occurrence in plants of calmodulin (CaM) but also of other sets of plant-specific Ca2+ sensors such as calmodulin-like proteins (CMLs), Ca2+-dependent protein kinases (CDPKs) and calcineurin B-like proteins (CBLs) indicate that plants possess specific tools and machineries to convert Ca2+ signals into appropriate responses. Here, we focus on recent progress made in monitoring the generation of Ca2+ signals at the whole plant or cell level and their long distance propagation during biotic interactions. The contribution of CaM/CMLs and CDPKs in plant immune responses mounted against bacteria, fungi, viruses and insects are also presented

Composting of sugar cane bagasse by Bacillus strains

Composting of sugar cane bagasse with Bacillus sp. CMAGI2 and Bacillus subtilis JCM 1465T strains was carried out during five months at horticultural center. Chemical, biochemical and microbial parameters were followed during this process. There was a difference between inoculated composts and non-inoculated compost. These bacterial additives allowed greater biodegradation compared to control compost. The inoculated composts were more degraded than the control compost with compost3 which presented the highest OM loss with 91.37%, compost1 with 90.15% and compost2 had 89.47% of OM loss. Control compost showed the lowest C/N ratio, however compost3 had the highest C/N ratio compared to compost1 and compost2. Microbiologically, Bacillus strains in compost1 and compost2 had probably inhibitory effect on microflora statistically if they were inoculated alone when the mixture of two strains (compost3) had no inhibitory effect on microflora during the composting process. The inoculated composts presented higher enzymatic activities than control compost, probably due to the presence of Bacillus strains.Key words: Sugar cane bagasse, composting, Bacillus sp.CMAGI2, Bacillus subtilis JCM 1465T

Phylotranscriptomics of the Pentapetalae Reveals Frequent Regulatory Variation in Plant Local Responses to the Fungal Pathogen Sclerotinia sclerotiorum

Comparative transcriptome analyses reveal a major contribution of regulatory divergence in conserved genes during the response of Pentapetalae plants to the fungal pathogen Sclerotinia sclerotiorum. Quantitative disease resistance (QDR) is a conserved form of plant immunity that limits infections caused by a broad range of pathogens. QDR has a complex genetic determinism. The extent to which molecular components of the QDR response vary across plant species remains elusive. The fungal pathogen Sclerotinia sclerotiorum, causal agent of white mold diseases on hundreds of plant species, triggers QDR in host populations. To document the diversity of local responses to S. sclerotiorum at the molecular level, we analyzed the complete transcriptomes of six species spanning the Pentapetalae (Phaseolus vulgaris, Ricinus communis, Arabidopsis [Arabidopsis thaliana], Helianthus annuus, Solanum lycopersicum, and Beta vulgaris) inoculated with the same strain of S. sclerotiorum. About one-third of plant transcriptomes responded locally to S. sclerotiorum, including a high proportion of broadly conserved genes showing frequent regulatory divergence at the interspecific level. Evolutionary inferences suggested a trend toward the acquisition of gene induction relatively recently in several lineages. Focusing on a group of ABCG transporters, we propose that exaptation by regulatory divergence contributed to the evolution of QDR. This evolutionary scenario has implications for understanding the QDR spectrum and durability. Our work provides resources for functional studies of gene regulation and QDR molecular mechanisms across the Pentapetalae