Biology subjects

Halter, T.

Publications and source records attributed to Halter, T..

7 recordsLinked to original sources

bioRxiv2025

Arabidopsis HYPERSENSITIVE INDUCED REACTION 2 affects plasma membrane receptor pathways and organization

The distribution of proteins across the plasma membrane is not uniform; however, the principles governing their organization remain not fully understood. Hypersensitive-induced reaction (HIR) proteins are plant-specific members of the stomatin/prohibitin/flotillin/HflK/C (SPFH) family that have been shown to influence membrane organization. Arabidopsis thaliana HIR2 interacts with multiple plasma membrane proteins, including receptor kinases such as BAK1-INTERACTING RECEPTORS 2 and 3 (BIR2 and 3), BRI1-ASSOCIATED KINASE 1 (BAK1), FLAGELLIN SENSING 2 (FLS2), and BRASSINOSTEROID INSENSITIVE 1 (BRI1). These interactions connect HIR2 to BAK1-mediated signaling pathways, as evidenced by impaired growth and immunity phenotypes in hir2 mutants. HIR2 is anchored to the inner leaflet of the plasma membrane through a hydrophobic interaction domain and S-acylation. Using single-particle tracking photoactivated localization microscopy (sptPALM), we showed that HIR2 affects receptor kinase dynamics and clustering, suggesting a role in spatially coordinating receptor complex activities. Structural modeling with AlphaFold 3 predicts a multimeric circular cup-like assembly for HIR2, consistent with high molecular weight complexes identified through blue native polyacrylamide gel electrophoresis. These findings indicate that HIR2 forms a discrete membrane compartment, providing a novel structural framework for spatial membrane organization and thereby modulating the function of membrane-resident receptors.

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

A novel widespread MITE element in the repeat-rich genome of the Cardinium endosymbiont of the spider Oedothorax gibbosus

Free-living bacteria have evolved multiple times to become host-restricted endosymbionts. The transition from a free-living to a host-restricted lifestyle comes with a number of different genomic changes, including a massive loss of genes. In host-restricted endosymbionts, gene inactivation and genome reduction is facilitated by mobile genetic elements, mainly insertion sequences (ISs). ISs are small autonomous mobile elements, and one of, if not the most, abundant transposable elements in bacteria. Proliferation of ISs is common in some facultative endosymbionts, and is likely driven by the transmission bottlenecks, which increase the level of genetic drift. In the current study we present a manually curated genome annotation for a Cardinium endosymbiont of the dwarf spider Oedothorax gibbosus. Cardinium species are host-restricted endosymbionts that, similarly to Wolbachia spp., include strains capable of manipulating host reproduction. Through the focus on mobile elements, the annotation revealed a rampant spread of ISs, extending earlier observations in other Cardinium genomes. We found that a large proportion of IS elements are actually pseudogenised, with many displaying evidence of recent inactivation. Most notably, we describe the lineage-specific emergence and spread of a novel IS-derived Miniature Inverted repeat Transposable Element (MITE), likely being actively maintained by intact copies of its parental IS982-family element. This work highlights the relevance of manual curation of these repeat-rich endosymbiont genomes for the discovery of novel MITEs, as well as the possible role these understudied elements might play in genome streamlining.

genomics↗

bioRxiv2022

One to host them all: genomics of the diverse bacterial endosymbionts of the spider Oedothorax gibbosus

Bacterial endosymbionts of the groups Wolbachia, Cardinium and Rickettsiaceae are well-known for their diverse effects on their arthropod hosts, ranging from mutualistic relationships to reproductive phenotypes. Here, we analyzed a unique system in which the dwarf spider Oedothorax gibbosus is co-infected with up to five different endosymbionts affiliated with Wolbachia, Candidatus Tisiphia (formerly Torix group Rickettsia), Cardinium, and Rhabdochlamydia. Using short-read genome sequencing data, we show that the endosymbionts are heterogeneously distributed among O. gibbosus populations and are frequently found co-infecting spider individuals. To study this intricate host-endosymbiont system on a genome resolved level, we used long-read sequencing to reconstruct closed genomes of the Wolbachia, Ca. Tisiphia and Cardinium endosymbionts. We provide insights in the ecology and evolution of the endosymbionts and shed light on the interactions with their spider host. We detected high quantities of transposable elements in all endosymbiont genomes and provide evidence that ancestors of the Cardinium, Ca. Tisiphia and Wolbachia endosymbionts have co-infected the same hosts in the past. Our findings contribute to broadening our knowledge about endosymbionts infecting one of the largest animal phyla on earth and show the usefulness of transposable elements as an evolutionary "contact-tracing" tool. Data summaryAll supporting data, code and protocols have been provided within the article or through supplementary data files. Seven supplementary figures and seven supplementary tables are available with the online version of this article. Sequencing data used in this study was generated and previously published by Hendrickx et al., 2021. Genome assemblies generated in this study have been deposited under the project PRJEB52003 at DDBJ/ENA/GenBank. The MAG of R. oedothoracis OV001 was deposited at DDBJ/ENA/GenBank under the sample SAMN28026840. The genome of Candidatus Rhabdochlamydia oedothoracis W744x776 was previously published by Halter et al., 2022 and is available at DDBJ/ENA/GenBank (accession: CP075587-CP075588). The collection of genomes and proteomes, all files for phylogenetic analyses including gene alignments, concatenated alignments, and tree files, and original output files of the HGT and SNP predictions used in this study are available at zenodo (https://doi.org/10.5281/zenodo.6362846).

genomics↗

bioRxiv2022

Ecology and evolution of chlamydial symbionts of arthropods

The phylum Chlamydiae consists of obligate intracellular bacteria including major human pathogens and diverse environmental representatives. Here we investigated the Rhabdochlamydiaceae, which is predicted to be the largest and most diverse chlamydial family, with the few described members known to infect arthropod hosts. Using published 16S rRNA gene sequence data we identified at least 388 genus-level lineages containing about 14 051 putative species within this family. We show that rhabdochlamydiae are mainly found in freshwater and soil environments, suggesting the existence of diverse, yet unknown hosts. Next, we used a comprehensive genome dataset including metagenome assembled genomes classified as members of the family Rhabdochlamydiaceae, and we added novel complete genome sequences of Rhabdochlamydia porcellionis infecting the woodlouse Porcellio scaber, and of Candidatus R. oedothoracis associated with the linyphiid dwarf spider Oedothorax gibbosus. Comparative analysis of basic genome features and gene content with reference genomes of well-studied chlamydial families with known host ranges, namely Parachlamydiaceae (protist hosts) and Chlamydiaceae (human and other vertebrate hosts) suggested distinct niches for members of the Rhabdochlamydiaceae. We propose that members of the family represent intermediate stages of adaptation of chlamydiae from protists to vertebrate hosts. Within the genus Rhabdochlamydia, pronounced genome size reduction could be observed (1.49-1.93 Mb). The abundance and genomic distribution of transposases suggests transposable element expansion and subsequent gene inactivation as a mechanism of genome streamlining during adaptation to new hosts. This type of genome reduction has never been described before for any member of the phylum Chlamydiae. This study provides new insights into the molecular ecology, genomic diversity, and evolution of representatives of one of the most divergent chlamydial families.

genomics↗

bioRxiv2020

The Arabidopsis demethylase ROS1 cis-regulates defense genes by erasing DNA methylation at promoter-regulatory regions

Active DNA demethylation has emerged as an important regulatory process of plant and mammalian immunity. However, very little is known about the mechanisms by which active demethylation controls transcriptional immune reprogramming and disease resistance. Here, we first show that the Arabidopsis active demethylase ROS1 promotes basal resistance towards Pseudomonas syringae by antagonizing RNA-directed DNA methylation (RdDM). Furthermore, we found that ROS1 facilitates the flagellin-triggered induction of the disease resistance gene RMG1 by limiting RdDM at the 3 boundary of a remnant RC/Helitron transposable element (TE) embedded in its promoter. We further identify flagellin-responsive ROS1 putative primary targets, and show that at a subset of promoters, ROS1 erases methylation at discrete regions exhibiting WRKY transcription factors (TFs) binding. In particular, we demonstrate that ROS1 removes methylation at the orphan immune receptor RLP43 promoter, to ensure DNA binding of WRKY TFs. Finally, we show that ROS1-directed demethylation of the RMG1 and RLP43 promoters is causal for both flagellin responsiveness of these genes and for basal resistance. Overall, these findings significantly advance our understanding of how active demethylases shape transcriptional immune reprogramming to enable antibacterial resistance. HIGHLIGHTSO_LIThe TNL RMG1 that is regulated by ROS1 positively regulates basal resistance towards Pto DC3000 C_LIO_LIROS1 regulates the flg22-triggered differential expression of more than 2000 thousands genes, among which 10% are demethylated by ROS1 C_LIO_LIROS1 facilitates the transcriptional activation of a subset of flg22-induced genes by antagonizing RdDM at discrete promoter regions C_LIO_LIWRKY transcription factors (TFs) bind to the demethylated promoter regions of a subset of flg22-induced ROS1 targets C_LIO_LIThe hypermethylation at the RLP43 promoter, caused by the lack of ROS1, repels DNA binding of two PAMP-responsive WRKY TFs C_LIO_LISpecific hypermethylation at the ROS1-targeted promoter regions of RMG1 and RLP43 is causal for their silencing as well as for disease susceptibility against Pto DC3000 C_LI

genomics↗

bioRxiv2020

Low ribosomal RNA genes copy number provoke genomic instability and chromosomal segment duplication events that modify global gene expression and plant-pathogen response

Among the hundreds of ribosomal RNA (rRNA) gene copies organized as tandem repeats in the nucleolus organizer regions (NORs), only a portion is usually actively expressed in the nucleolus and participate in the ribosome biogenesis process. The role of these extra-copies remains elusive, but previous studies suggested their importance in genome stability and global gene expression. Because the nucleolus is also a platform for nuclear organization, we tested the impact of a decreased amount of rRNA gene copies on the Arabidopsis thaliana 3D genome organization and stability, using an A. thaliana line only containing 20% of rRNA gene copies (20rDNA line). Compared to the wild-type Col-0, the 20rDNA line shows several signs of genomic instability, such as variations in 3D genome organization, spontaneous double-strand breaks accumulation, transcriptomic changes, and higher DNA methylation level. Strikingly, using genomic and microscopic approaches, we identified seven large tandem duplications in direct orientation (TDDOs) ranging from 60 kb to 1.44 Mb. As a consequence, more than 600 genes were duplicated, often associated with an increase in their expression level. Among them, we found several upregulated genes involved in plant-pathogen response, which could explain why the 20rDNA line is hyper-resistant to both bacterial and nematode infections. Finally, we show that the TDDOs create gene fusions and/or truncations and we discuss their potential implications on plant genome evolution.

plant biology↗