Biology subjects

Blanc-Mathieu, R.

Publications and source records attributed to Blanc-Mathieu, R..

13 recordsLinked to original sources

bioRxiv2025

Beyond binding motif: genomic context predicts transcription factor dependent regulation in Arabidopsis

Transcription Factors (TFs) play a crucial role in the spatiotemporal control of gene expression. Despite the presence of many potential TF binding sites (TFBS) across the genome, TFs do not interact with all of them, and, among those, only a subset leads to actual regulation. In this work, we investigate how the genomic context of a putative TFBS, including the occurrence of binding motifs for other TFs, can be used to predict effective transcriptional regulation by a TF of interest. We focus on LEAFY (LFY), a plant-specific TF and master regulator of flower development. Using available transcriptomes and TF-DNA binding experiments, we identify 1164 LFY binding sites associated with a regulatory response in Arabidopsis thaliana. We then apply a machine learning approach based on properties of the surrounding genomic region, to discriminate these regulatory LFY binding sites from non-regulatory ones. Detailed analysis of the models components reveals that, for LFY, the density and quality of binding sites constitute the most important features but were not sufficient on their own to predict regulatory activity. The presence of binding sites for other transcription factors and the overall richness in TFBS were also essential. These results clarify the nature of the regulatory code by which LFY operates and could serve as a basis for the study of the regulatory elements of other transcription factors. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=134 SRC="FIGDIR/small/655699v1_ufig1.gif" ALT="Figure 1"> View larger version (27K): org.highwire.dtl.DTLVardef@1a1a80org.highwire.dtl.DTLVardef@1c1fee5org.highwire.dtl.DTLVardef@1457164org.highwire.dtl.DTLVardef@176c46_HPS_FORMAT_FIGEXP M_FIG C_FIG

plant biology↗

bioRxiv2023

SEPALLATA-driven MADS transcription factor tetramerization is required for inner whorl floral organ development

MADS genes encode transcription factors that act as master regulators of plant reproduction and flower development. The SEPALLATA (SEP) subfamily is required for the development of floral organs and plays roles in inflorescence architecture and development of the floral meristem. The SEPALLTAs act as organizers of MADS complexes, forming both heterodimers and heterotetramers in vitro. To date, the MADS complexes characterized in angiosperm floral organ development contain at least one SEPALLATA protein. Whether DNA-binding by SEPALLATA-containing dimeric MADS complexes are sufficient for launching floral organ identity programs, however, is not clear as only defects in floral meristem determinacy were observed in tetramerization impaired SEPALLATA mutants. Here, we used a combination of genome-wide binding studies, high resolution structural studies of the SEP3/AGAMOUS tetramerization domain, structure-based mutagenesis and complementation experiments in sep1 sep2 sep3 and sep1 sep2 sep3 ag-4 plants transformed with versions of SEP3 encoding tetramerization mutants. We demonstrate that while SEP3 heterodimers are able to bind DNA both in vitro and in vivo and recognize the majority of SEP3 wild type binding sites genome-wide, tetramerization is not only required for floral meristem determinacy, but also absolutely required for floral organ identity in the second, third and fourth whorls.

plant biology↗

bioRxiv2022

Plant-TFClass: a structural classification for plant transcription factors

Transcription factors (TFs) bind DNA at specific sequences to regulate gene expression. This universal process is achieved thanks to the DNA-binding domain (DBD) present in each TF. DBDs show a vast diversity of protein folds within and across organisms, ranging from simple long basic alpha helices to complex structural combinations of alpha, beta and loop folds. In mammals, the structural conformation of the DBDs and the way it establishes contact with DNA has been used to organize TFs in a hierarchical classification named TFClass. However, such classification is missing from plants that possess many DBD types absent from mammals. Here, we reviewed the numerous TF DBD 3D-structures and models available for plants to organize all plant TFs types following the TFClass hierarchy (Superclass/Class/Family/Subfamily). We classified most of the 55 recognized plant TF types within the existing TFClass framework. This extended classification led us to add six new classes and 34 new families corresponding to TF DBD structures absent in mammals. Plant-TFClass provides a unique resource for TF and TF binding sites comparison across TF families and across organisms.

plant biology↗

bioRxiv2022

DNA methylation at a single cytosine embedded in the W-box cis-element repels binding of WRKY transcription factors through steric hindrance

Previously, we showed that the Arabidopsis active demethylase ROS1 prunes DNA methylation at the promoters of a subset of immune-responsive genes to facilitate their transcriptional activation during antibacterial defence (Halter et al., 2021). In particular, ROS1 was shown to demethylate the RLP43 promoter in a region carrying a functional W-box cis-element, thereby ensuring a tight binding of WRKY transcriptional factors (TFs) onto DNA. Here, we first extend these findings by showing that DNA methylation at W-box elements decreases the binding of several Arabidopsis WRKY TFs in vitro. Furthermore, we provide evidence that DNA methylation at a single cytosine located in the W-box of the RLP43 promoter strongly repels DNA binding of an Arabidopsis WRKY TF in vitro. Using structural modelling, we demonstrate that this cytosine interacts through van der Waals contacts with the conserved tyrosine of WRKY DNA binding domains. Significantly, our model predicts steric hindrance when a 5-methyl group is present on this specific cytosine, thereby likely preventing tight binding of WRKY DNA binding domains. Finally, because the WRKY motif and the residues involved in DNA contacts are conserved, we propose that this methylation-dependent WRKY-DNA binding inhibitory mechanism must be widespread across plant species.

plant biology↗

bioRxiv2022

Genome analysis of Parmales, a sister group of diatoms, reveals the evolutionary specialization of diatoms from phago-mixotrophs to photoautotrophs

The order Parmales (Bolidophyceae) is a minor group of pico-sized eukaryotic marine phytoplankton that contains species with cells surrounded by silica plates. Previous studies revealed that Parmales is a member of ochrophytes and sister to diatoms (Bacillariophyta), the most successful phytoplankton group in the modern ocean. Therefore, parmalean genomes can serve as a reference to elucidate both the evolutionary events that differentiated these two lineages and the genomic basis for the ecological success of diatoms vs. the more cryptic lifestyle of parmaleans. Here, we compared the genomes of eight parmaleans and five diatoms to explore their physiological and evolutionary differences. Parmaleans were predicted to be phago-mixotrophs. By contrast, diatoms have undergone loss of genes related to phagocytosis, indicating the ecological specialization from phago-mixotroph to photoautotroph in the early evolution of diatoms. Furthermore, diatoms showed significant enrichment in gene sets involved in silica metabolism, nutrient uptake capacity, carbon concentrating mechanisms, and iron uptake in comparison with parmaleans. Overall, our results suggest a strong evolutionary link between the loss of phago-mixotrophy and specialization to a silicified photoautotrophic life stage early in diatom evolution after diverging from the Parmales lineage.

microbiology↗

bioRxiv2022

The F-box cofactor UFO redirects the LEAFY floral regulator to novel cis-elements

In angiosperms, flower patterning requires the localized expression of the APETALA3 (AP3) floral homeotic gene involved in petal and stamen development. AP3 is synergistically induced by the master transcription factor (TF) LEAFY (LFY) and the F-box protein UNUSUAL FLORAL ORGANS (UFO), but the molecular mechanism underlying this synergy has remained unknown. Here we show that the connection to ubiquitination pathways suggested by the F-box domain of UFO is mostly dispensable for its function and that UFO instead acts by forming a transcriptional complex with LFY and binds to newly discovered regulatory elements. Cryo-electron microscopy explains how a LFY-UFO complex forms on these novel DNA sites due to direct interaction of UFO with LFY and DNA. Finally, we show that this complex has a deep evolutionary origin, largely predating flowering plants. This work reveals a novel mechanism of an F-box protein in directly modulating the DNA-binding specificity of a master TF.

plant biology↗

bioRxiv2021

The Intervening Domain Is Required For DNA-binding and Functional Identity of Plant MADS Transcription Factors

The MADS transcription factors (TF) are an ancient protein family with a high degree of sequence identity that bind almost identical DNA sequences across all eukaryotic kingdoms of life, yet fulfill dramatically different physiological roles. In plants, the family is divided into two main lineages, type I and II, based on sequence conservation of the DNA-binding MADS-box domain (M domain) with yeast and animal M domains. Here, we demonstrate that DNA binding in both lineages absolutely requires a short amino acid sequence C-terminal to the M domain called the Intervening domain (I domain) in type II MADS. Structural elucidation of the MI domains from the floral regulator, SEPALLATA3 (SEP3), shows a highly conserved MADS-box fold with the I domain forming an alpha helix and acting to stabilize the M domain. Based on secondary structure prediction, sequences fulfilling the same function as the SEP3 I domain can be found in both lineages of plant MADS TFs, suggesting the I domain is a conserved and required part of the DNA-binding domain. Using the floral organ identity MADS TFs, SEP3, APETALA1 (AP1) and AGAMOUS (AG), domain swapping demonstrate that the I domain alters DNA-binding specificity based on seq-DAP-seq experiments. Yeast 2-hybrid experiments further revealed the role of the I domain in dimerization specificity. Surprisingly, introducing AG carrying the I domain of AP1 in the Arabidopsis ap1 mutant, resulted in a high degree of complementation and restoration of first and second whorl organs. Taken together, these data demonstrate that the I domain acts both as an integral part of the DNA-binding domain and strongly contributes to the functional identity of the MADS TF.

plant biology↗

bioRxiv2021

Year-round dynamics of amplicon sequence variant communities differ among eukaryotes, Mimiviridae, and prokaryotes in a coastal ecosystem

Coastal seawater is the habitat of different microbial communities. These communities are affected by seasonal environmental changes and fluctuating nutrient availability, as well as competitive and cooperative interspecific interactions. In this work, we investigated the seasonal dynamics of communities of eukaryotes, a major group of double-stranded DNA viruses infecting eukaryotes (i.e. Mimiviridae), as well as prokaryotes in the Uranouchi Inlet, Kochi, Japan. We performed metabarcoding using ribosomal RNA genes and the Mimiviridae polB gene as marker genes in 43 seawater samples collected during 20 months. Communities characterized by the compositions of amplicon sequence variants (ASVs) showed synchronic seasonal cycles for eukaryotes, Mimiviridae, and prokaryotes. However, the community dynamics showed intriguing differences in several aspects such as the recovery rate after a year. We further show that the differences in the community dynamics can be explained by differences in the recurrence/persistence levels of individual ASVs among eukaryotes, Mimiviridae, and prokaryotes. Mimiviridae ASVs were less persistent than eukaryotic ASVs, and prokaryotic ASVs were the most persistent. We argue that the differences in the specificity of interactions (i.e. virus-eukaryote vs prokaryote-eukaryote) as well as the survival strategies are at the origin of the distinct community dynamics among eukaryotes, Mimiviridae, and prokaryotes. One sentence summaryA one year observation of coastal microbial communities revealed similar but different community dynamics for eukaryotes, a group of large viruses, and prokaryotes.

microbiology↗

bioRxiv2021

The LEAFY floral regulator displays pioneer transcription factor properties

Pioneer transcription factors (TFs) are a special category of TFs with the capacity to bind to closed chromatin regions in which DNA is wrapped around histones and often highly methylated. Subsequently, they are able to modify the chromatin state to initiate gene expression. In plants, LEAFY (LFY) is a master floral regulator and has been suggested to act as a pioneer TF in Arabidopsis. Here, we demonstrate that LFY is able to bind both methylated and non-methylated DNA using a combination of in vitro genome-wide binding experiments and structural modeling. Comparisons between regions bound by LFY in vivo and chromatin accessibility data suggest that LFY binds a subset of regions occupied by nucleosomes. We confirm that LFY is able to bind nucleosomal DNA in vitro using reconstituted nucleosomes. Finally, we show that constitutive LFY expression in seedling tissues is sufficient to induce chromatin accessibility in the LFY direct target genes, APETALA1 and AGAMOUS. Taken together, our study suggests that LFY possesses key pioneer TF features that contribute to launch the floral gene expression program.

plant biology↗

bioRxiv2020

Quantitative assessment of NCLDV-host interactions predicted by co-occurrence analyses

Nucleocytoplasmic DNA viruses (NCLDVs) are highly diverse and abundant in marine environments. However, knowledge of their hosts is limited because only a few NCLDVs have been isolated so far. Taking advantage of the recent large-scale marine metagenomics census, in silico host prediction approaches are expected to fill the gap and further expand our knowledge of virus-host relationships for unknown NCLDVs. In this study, we built co-occurrence networks of NCLDVs and eukaryotic taxa to predict virus-host interactions using Tara Oceans sequencing data. Using the positive likelihood ratio to assess the performance of host prediction for NCLDVs, we benchmarked several co-occurrence approaches and demonstrated an increase in the odds ratio of predicting true positive relationships four-fold compared with random host predictions. To further refine host predictions from high-dimensional co-occurrence networks, we developed a phylogeny-informed filtering method, Taxon Interaction Mapper, and showed it further improved the prediction performance by twelve-fold. Finally, we inferred virophage - NCLDV networks to corroborate that co-occurrence approaches are effective for predicting interacting partners of NCLDVs in marine environments. ImportanceNCLDVs can infect a wide range of eukaryotes although their life cycle is less dependent on hosts compared with other viruses. However, our understanding of NCLDV- host systems is highly limited because few of these viruses have been isolated so far. Co-occurrence information has been assumed to be useful to predict virus-host interactions. In this study, we quantitatively show the effectiveness of co-occurrence inference for NCLDV host prediction. We also improve the prediction performance with a phylogeny-guided method, which leads to a concise list of candidate host lineages for three NCLDV families. Our results underpin the usage of co-occurrence approach for metagenomic exploration of the ecology of this diverse group of viruses.

microbiology↗

bioRxiv2020

The genome of a persistent giant algal virus encodes an unprecedented number of genes involved in energy metabolism

Viruses have long been viewed as entities possessing extremely limited metabolic capacities. Over the last decade, however, this view has been challenged, as metabolic genes have been identified in viruses possessing large genomes and virions--the synthesis of which is energetically demanding. Here, we unveil peculiar phenotypic and genomic features of Prymnesium kappa virus RF01 (PkV RF01), a giant virus of the Mimiviridae family. We found that this virus encodes an unprecedented number of proteins involved in energy metabolism, such as all four succinate dehydrogenase (SDH) subunits (A-D) as well as key enzymes in the {beta}-oxidation pathway. The SDHA gene was transcribed upon infection, indicating that the viral SDH is actively used by the virus-- potentially to modulate its hosts energy metabolism. We detected orthologous SDHA and SDHB genes in numerous genome fragments from uncultivated marine Mimiviridae viruses, which suggests that the viral SDH is widespread in oceans. PkV RF01 was less virulent compared with other cultured prymnesioviruses, a phenomenon possibly linked to the metabolic capacity of this virus and suggestive of relatively long co-evolution with its hosts. It also has a unique morphology, compared to other characterized viruses in the Mimiviridae family. Finally, we found that PkV RF01 is the only alga-infecting Mimiviridae virus encoding two aminoacyl-tRNA synthetases and enzymes corresponding to an entire base-excision repair pathway, as seen in heterotroph-infecting Mimiviridae. These Mimiviridae encoded-enzymes were found to be monophyletic and branching at the root of the eukaryotic tree of life. This placement suggests that the last common ancestor of Mimiviridae was endowed with a large, complex genome prior to the divergence of known extant eukaryotes. ImportanceViruses on Earth are tremendously diverse in terms of morphology, functionality, and genomic composition. Over the last decade, the conceptual gap separating viruses and cellular life has tightened because of the detection of metabolic genes in viral genomes that express complex virus phenotypes upon infection. Here, we describe Prymnesium kappa virus RF01, a large alga-infecting virus with a unique morphology, an atypical infection profile, and an unprecedented number of genes involved in energy metabolism (such as the tricarboxylic (TCA) cycle and the {beta}-oxidation pathway). Moreover, we show that the gene corresponding to one of these enzymes (the succinate dehydrogenase subunit A) is transcribed during infection and is widespread among marine viruses. This discovery provides evidence that a virus has the potential to actively regulate energy metabolism with its own gene.

microbiology↗

bioRxiv2019

Viruses of the eukaryotic plankton are predicted to increase carbon export efficiency in the global sunlit ocean

The biological carbon pump, in which carbon fixed by photosynthesis is exported to the deep ocean through sinking, is a major process in Earths carbon cycle. The proportion of primary production that is exported is termed the carbon export efficiency (CEE). Based on in-lab or regional scale observations, viruses were previously suggested to affect the CEE (i.e., viral "shunt" and "shuttle"). In this study, we tested associations between viral community composition and CEE measured at a global scale. A regression model based on relative abundance of viral marker genes explained 67% of the variation in CEE. Viruses with high importance in the model were predicted to infect ecologically important hosts. These results are consistent with the view that the viral shunt and shuttle functions at a large scale and further imply that viruses likely act in this process in a way dependent on their hosts and ecosystem dynamics.

ecology↗

bioRxiv2019

KofamKOALA: KEGG ortholog assignment based on profile HMM and adaptive score threshold

SummaryKofamKOALA is a web server to assign KEGG Orthologs (KOs) to protein sequences by homology search against a database of profile hidden Markov models (KOfam) with pre-computed adaptive score thresholds. KofamKOALA is faster than existing KO assignment tools with its accuracy being comparable to the best performing tools. Function annotation by KofamKOALA helps linking genes to KEGG resources such as the KEGG pathway maps and facilitates molecular network reconstruction.\n\nAvailabilityKofamKOALA, KofamScan, and KOfam are freely available from https://www.genome.jp/tools/kofamkoala/\n\nContactogata@kuicr.kyoto-u.ac.jp

bioinformatics↗