Biology subjects

Bourbousse, C.

Publications and source records attributed to Bourbousse, C..

15 recordsLinked to original sources

bioRxiv2026

Centromeric origin of Arabidopsis interstitial telomeric repeat domains

The mechanisms underlying the emergence of new DNA repeat classes remain poorly understood. One such example is the formation of interstitial telomeric repeat (ITR) domains commonly viewed as telomere-fossil byproducts of chromosome rearrangements. Here, we report that in Arabidopsis thaliana, ITRs arise from centromeres as centromeric-telomeric mosaic satellites that expand into higher-order structures via in situ amplification. Long-read sequencing of mutation accumulation lines and forward simulations of mutational processes confirmed the propensity of centromeres to form telomeric motifs. During establishment, ITRs adopt an atypical chromatin state that excludes CENH3 incorporation, thereby enabling escape from the functional constraints of centromere identity. Accordingly, a pangenomic survey of natural accessions showed that ITRs vary abruptly and independently of telomere length, notably through transposon-associated block duplications. These findings identify centromeres as major sources of telomeric sequences and an original route for the emergence of new DNA satellite types.

genomics↗

bioRxiv2025

Arabidopsis YEATS domain proteins facilitate DNA double strand break repair via homologous recombination pathways

DNA double-strand break (DSB) repair is required to maintain genome integrity and organismal fitness. This process occurs within chromatin and although accurate repair requires extensive changes in chromatin structure and composition, chromatin effectors facilitating DSB repair remain largely unknown in plants. Using reverse genetics, we identified two chromatin readers, YAF9A and YAF9B, as new factors required for DSB repair in Arabidopsis. While only YAF9B is induced by DNA damage, both YAF9A and YAF9B are required for DSB repair, including via homologous recombination (HR)-like pathways. Mechanistically, we found YAF9A and YAF9B denote distinct remodeling complexes: While YAF9A associates with both NuA4 and SWR1, YAF9B only associates with NuA4, defining a DNA-damage-specific version of this remodeling complex and revealing the first link between NuA4 and DSB repair in plants. We also uncovered direct roles for YAF9A and YAF9B in DNA repair, rather than indirect roles in gene regulation, as yaf9 mutants showed normal transcriptional responses to DNA damage. Finally, we demonstrate that the YAF9B reader domain is required for DSB repair. These results link YAF9A, YAF9B, and their respective remodeling complexes, to DSB repair in a histone reader-dependent manner, expanding our understanding of how chromatin effectors regulate DSB repair in plants.

plant biology↗

bioRxiv2025

Linker Histones Enhance Robustness in Diurnal Transcription Dynamics.

Linker histone H1 is crucial for chromatin organization and gene expression in Arabidopsis thaliana, influencing development and stress responses. To explore its role in diurnal gene regulation, we examined H1-deficient plants and found that H1 is essential for maintaining rhythmic gene expression. Genes losing synchronization often contained NAC transcription factor binding sites, indicating H1 may affect their accessibility. Nuclear imaging revealed that H1 subtly modulates nuclear size and chromatin distribution across the photoperiod. Epigenetic analysis showed typical diurnal changes--declines in H3K4me3 and active RNA Pol II in the evening and increases in H3K27me3. In H1 mutants, these patterns persisted but with elevated H3K4me3 and RNA Pol II (Ser2P) levels at night and in the morning. These results suggest that H1 fine-tunes chromatin and transcriptional rhythms, contributing to the temporal coordination of gene activity in response to environmental and developmental signals.

plant biology↗

bioRxiv2025

Entry and exit of Fragilariopsis cylindrus diatoms from the polar night: evidence for chromatin-mediated genome control

Regulation of the epigenome landscape plays a crucial role in adaptation to environmental changes. However, the molecular mechanisms by which epigenome landscapes are established and tuned to adjust the cellular status to environmental cues remain poorly understood, especially in unicellular photosynthetic eukaryotes. Polar microalgae must adapt to extreme variations in light and temperature for survival and therefore represent excellent models to understand the diversity of gene regulatory mechanisms, yet chromatin-based mechanisms have never been explored in these organisms. In this study, we combined genome-wide profiling of histone and DNA modifications with transcriptomic analyses of the marine polar diatom Fragilariopsis cylindrus upon entry and exit of a 3-month-long polar night. We show that, in agreement with its established role in transcription facilitation, histone H2B monobiquitination (H2Bub) is modulated at active genes upon prolonged darkness to light re-exposure. In contrast, histone H3 lysine 27 trimethylation (H3K27me3) and DNA cytosine methylation (CG methylation), two modifications typically associated with the silencing of genes or transposable elements (TEs), remained stable throughout the transitions, reinforcing their role in transcriptional repression, particularly at TEs but also at a few genes. We further demonstrate that H3K27me3 and DNA methylation are physically associated at TEs, probably reflecting a dual locking system enabling F.cylindrus cells to cope with the invasive nature of these genetic elements under extreme environmental conditions. These findings enhance our understanding of genome and epigenome regulation in diatoms in response to environmental variability and open new avenues for exploring the role played by chromatin-level regulation in the unique evolutionary history of polar unicellular eukaryotes.

genomics↗

bioRxiv2025

Genome-scale transcriptome augmentation during Arabidopsis thaliana photomorphogenesis

Plant photomorphogenesis is a light-induced developmental switch that combines massive reprogramming of gene expression and a general enhancement in RNA Polymerase II activity. Yet, transcriptome analyses have failed to demonstrate a clear tendency toward gene upregulation. To solve this conundrum, we optimized a spike-in RNA-seq experimental and analysis pipeline and reconciled transcriptome dynamics with epigenomic and cytogenetic observations. We found that light induces a two-fold expansion of the transcriptome during Arabidopsis thaliana cotyledon photomorphogenesis, with 94% of the 9,128 differentially expressed genes being upregulated within the first six hours. Transcriptome augmentation was further detected at a similar strength in spike-free RNA-seq datasets from independent laboratories renormalized using stable genes that mimic the spike-in information. On this new basis, reinterpretation of light-mediated gene regulatory pathways revealed a quasi-exclusive positive effect of HY5 and other key light-induced transcription factors at target genes. This new standpoint unveiled the unilateral impact of light on the transcriptome of Arabidopsis cotyledons at the genome scale and opens new avenues for investigating global genome regulation during plant developmental and environmental responses.

plant biology↗

bioRxiv2024

An active light signalling pathway is necessary for ABA-induced inhibition of hypocotyl elongation.

Driven by cell elongation, hypocotyl growth is tightly controlled by light and responds to external stimuli and endogenous hormonal pathways. Hypocotyls are known to be responsive to the stress signalling hormone abscisic acid (ABA) which effectively inhibits cell elongation, but how this regulation is connected to light responses and other endogenous hormonal pathways has been a subject of limited studies. Here, we show that whereas hypocotyl elongation is sensitive to ABA in light-grown seedlings, the hypocotyl of dark-grown etiolated seedlings is ABA-insensitive. In the dark, hypocotyl sensitivity to ABA is restored in the constitutive photomorphogenic pifq and cop1-4 mutants, suggesting that an active light signalling pathway is necessary for hypocotyl responsiveness to ABA. However, etiolated hypocotyls retain ABA responsiveness, as could be detected by the induction of ABI1 and RD29B transcripts in response to exogenous ABA, suggesting that inhibition of hypocotyl elongation mediated by ABA does not follows the canonical ABA signalling dependent on transcription. Here, using RNA-seq analysis we identified a number of ABA differentially expressed genes (DEGs) that correlate with ABA inhibition of hypocotyl elongation, specifically in dark-grown pifq or light-grown WT plants, and whose expression remains unchanged by ABA treatment in dark-grown WT plants. Among these DEGs we identified a number of genes playing a role in cell elongation directly at the level of the plasma membrane, as SAURs, ion transporters, auxin flux regulators, channels, and cell wall modification enzymes. The use of the auxin transport inhibitor, NPA, revealed that in the light auxin transport impairment renders hypocotyls insensitive to ABA in WT and pifq plants. Thus, in the light, hypocotyl responsiveness to ABA is dependent on auxin transport and independent of PIFs. In the dark, PIFs render hypocotyls insensitive to ABA, perhaps by regulating the expression of a number of ABA DEGs, a mechanism that could allow plants to prioritize the elongation towards light, avoiding to slow-down soil emergence that could be induced by ABA signalling in case of sudden reduction of soil moisture.

plant biology↗

bioRxiv2023

Genome-wide evidence of the role of Paf1C in transcription elongation and histone H2B monoubiquitination in Arabidopsis

The evolutionarily conserved Paf1 complex (Paf1C) participates in transcription, and research in animals and fungi suggests that it facilitates RNAPII progression through chromatin remodeling. To obtain evidence that Paf1C acts in transcription elongation in Arabidopsis, we examined the genomic distribution of the ELF7 and VIP3 subunits of Paf1C. The occupancy of both subunits was confined to thousands of gene bodies and positively correlated with RNAPII occupancy and the level of gene expression, supporting a role as a transcription elongation factor. We found that monoubiquitinated histone H2B, which marks most transcribed genes, was strongly reduced genome-wide in elf7 seedlings. Genome-wide profiling of RNAPII revealed that in elf7 mutants, RNAPII occupancy was reduced throughout the gene body and at the transcription end site of Paf1C-targeted genes, suggesting a direct role for the complex in transcription elongation. Overall, our observations suggest that there is a direct functional link between Paf1C activity, mono-ubiquitination of histone H2B, and the transition of RNPII to productive elongation. However, for several genes, Paf1C may also act independently of H2Bub deposition or occupy these genes more stably than H2Bub marking, possibly reflecting the dynamic nature of Paf1C association and H2Bub turnover during transcription.

plant biology↗

bioRxiv2023

Distinct clades of TELOMERE REPEAT BINDING transcriptional regulators interplay to regulate plant development

TELOMERE REPEAT BINDING proteins (TRBs) are plant-specific transcriptional regulators that combine two DNA-binding domains, the GH1 domain shared with H1 histones that binds to linker DNA and the Myb/SANT domain that specifically recognizes the telobox DNA binding site motif. TRB1, TRB2 and TRB3 proteins recruit the Polycomb group complex 2 (PRC2) to deposit H3K27me3 and JMJ14 to remove H3K4me3 at target genes containing telobox motifs in their promoters to repress transcription. Here, we characterize the function of TRB4 and TRB5, which belong to a separate TRB clade conserved in spermatophytes. TRB4 and TRB5 affect the transcriptional control of several hundred genes involved in developmental responses to environmental cues, the majority of which differ from differentially regulated genes in trb1 trb2 trb3, suggesting distinct modes of action at the chromatin level. Indeed, TRB4 binds to several thousand sites in the genome, mainly at TSS and promoter regions of transcriptionally active and H3K4me3-marked genes but is not enriched at H3K27me3-marked gene bodies. TRB4 physically interacts with the PRC2 component CURLY LEAF (CLF), but, unexpectedly, loss of TRB4 and TRB5 partially suppresses the developmental defects of clf mutant plants, by acting as transcriptional activators of the key flowering genes SOC1 and FT. We further show that TRB4 and TRB1 share multiple target genes and reveal physical and genetic interactions between TRBs of the two distinct clades, collectively unveiling that TRB proteins engage in both positive and negative interactions with other members of the family to regulate plant development through PRC2-dependent and independent mechanisms.

plant biology↗

bioRxiv2023

Hypometabolism to survive the long polar night in the diatom Fragilariopsis cylindrus

Diatoms, the major eukaryotic phytoplankton in polar regions, are essential to sustain Arctic and Antarctic ecosystems. As such, it is fundamental to understand the physiological mechanisms and associated molecular basis of their resilience to the long polar night. Here, we report an integrative approach revealing that in prolonged darkness, diatom cells enter a state of quiescence associated with reduced metabolic and transcriptional activity during which no cell division occurs. We propose that minimal energy is provided by respiration and degradation of protein, carbohydrate, and lipid stores and that homeostasis is maintained by autophagy in prolonged darkness. We also report internal structural changes that manifest the morphological acclimation of cells to darkness. Our results further indicate that immediately following a return to light, diatom cells are able to use photoprotective mechanisms and rapidly resume photosynthesis. Cell division resumed rates similar to those before darkness. Our study demonstrates the remarkable robustness of polar diatoms to prolonged darkness at low temperatures. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=160 SRC="FIGDIR/small/524047v1_ufig1.gif" ALT="Figure 1"> View larger version (55K): org.highwire.dtl.DTLVardef@1da578corg.highwire.dtl.DTLVardef@1a9ac5borg.highwire.dtl.DTLVardef@729265org.highwire.dtl.DTLVardef@1e94c18_HPS_FORMAT_FIGEXP M_FIG C_FIG TeaserTo survive the long winter, polar diatoms slow down metabolism and express genes to assure survival following return to light.

ecology↗

bioRxiv2022

The UBP5 histone H2A deubiquitinase counteracts PRC2-mediated repression to regulate Arabidopsis development and stress responses

Polycomb Repressive Complexes (PRCs) control gene expression through the incorporation of H2Aub and H3K27me3. However, there is limited knowledge about PRCs interacting proteins and their interplay with PRCs in epigenome reshaping, which is fundamental to understand gene regulatory mechanisms. Here, we identified UBIQUITIN SPECIFIC PROTEASE 5 (UBP5) as a novel interactor of the PRC2 subunit SWINGER and its associated factor PWO1 in Arabidopsis thaliana. As inferred from the functional analyses of ubp5 CRISPR-Cas9 mutant plants, UBP5 regulates plant development and stress responses, notably by promoting H2A monoubiquitination erasure, leading to transcriptional de-repression. Preferential association of UBP5 at PRC2 recruiting motifs and local H3K27me3 gaining in ubp5 mutant plants further suggest the existence of functional interplays between UBP5 and PRC2 in regulating epigenome dynamics. In summary, UBP5 provides novel insights to disentangle the complex PRC2 interaction network and is a crucial regulator of the pivotal epigenetic repressive marks H2Aub and H3K27me3.

developmental biology↗

bioRxiv2021

The CLASSY family controls tissue-specific DNA methylation patterns in Arabidopsis

DNA methylation shapes the epigenetic landscape of the genome, plays critical roles in regulating gene expression, and ensures transposon silencing. As evidenced by the numerous defects associated with aberrant DNA methylation landscapes, establishing proper tissue-specific methylation patterns is critical. Yet, how such differences arise remains a largely open question in both plants and animals. Here we demonstrate that CLASSY1-4 (CLSY1-4), four locus-specific regulators of DNA methylation that are differentially expressed during plant development, play major roles in controlling tissue-specific DNA methylation patterns. Depending on the tissue, the genetic requirements for specific CLSYs differ significantly and, on a global scale, certain clsy mutants are sufficient to largely shift the epigenetic landscape between tissues. Together, these findings not only reveal substantial epigenetic diversity between tissues, but assign these changes to specific CLSY proteins, revealing how locus-specific targeting combined with tissue-specific expression enables the CLSYs to generate epigenetic diversity during plant development.

plant biology↗

bioRxiv2020

Histone H1 protects telomeric repeats from H3K27me3 invasion in Arabidopsis

While the pivotal role of linker histone H1 in shaping nucleosome organization is well established, its functional interplays with chromatin factors along the epigenome are just starting to emerge. Here we first report that in Arabidopsis, as in mammals, H1 occupies Polycomb Repressive Complex 2 (PRC2) target genes where it favors chromatin condensation and H3K27me3 deposition. We further show that, contrasting with its conserved function in PRC2 activation at genes, H1 selectively prevents H3K27me3 accumulation at telomeres and large pericentromeric interstitial telomeric repeat (ITR) domains by restricting DNA accessibility to Telomere Repeat Binding (TRB) proteins, a group of H1-related Myb factors mediating PRC2 cis recruitment. This study unveils a mechanistic framework by which H1 avoids the formation of gigantic H3K27me3-rich domains at telomeric sequences and contributes to safeguard nucleus architecture. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=128 SRC="FIGDIR/small/402172v5_ufig1.gif" ALT="Figure 1"> View larger version (33K): org.highwire.dtl.DTLVardef@13cf29dorg.highwire.dtl.DTLVardef@5c5c86org.highwire.dtl.DTLVardef@1be7516org.highwire.dtl.DTLVardef@f935cb_HPS_FORMAT_FIGEXP M_FIG Teano et al. report that that linker histone H1 and a group of H1-related telomeric proteins interplay to selectively influence the Polycomb repressive landscape at genes and telomeric repeats in Arabidopsis. These findings provide a mechanistic framework by which H1 influences the epigenome and nuclear organization in a sequence-specific manner. C_FIG HighlightsO_LIH1 promotes PRC2 activity and limits accessibility at a majority of genes C_LIO_LIH1 prevents PRC2 activity at telomeric DNA sequences C_LIO_LIPRC2 repression is achieved by restricting accessibility to TRB proteins C_LIO_LIH1 orchestrates the spatial organization of telomeres and interstitial telomeres (ITRs) C_LI

molecular biology↗

bioRxiv2020

DET1-mediated COP1 regulation avoids HY5 activity over second-site targets to tune plant photomorphogenesis

DE-ETIOLATED1 (DET1) is a negative regulator of plant photomorphogenesis acting as a component of the C3D complex, which can further associate to CULLIN4 to form a CRL4C3D E3 ubiquitin ligase. CRL4C3D is thought to act together with CRL4COP1SPA ubiquitin ligase, to promote the ubiquitin-mediated degradation of the master regulatory transcription factor ELONGATED HYPOCOTYL5 (HY5), thereby controlling photomorphogenic gene regulatory networks. Yet, functional links between COP1 and DET1 have long remained elusive. Here, upon mass spectrometry identification of DET1 and COP1-associated proteins, we provide in vivo evidence that DET1 associates with COP1 to promote its destabilization, a process necessary to dampen HY5 protein abundance. By regulating HY5 over-accumulation, DET1 is critical to avoid its association to second-site loci, including many PIF3 target genes. Accordingly, excessive HY5 levels result in an increased HY5 repressive activity and are sufficient to trigger fusca-like phenotypes otherwise observed typically in COP1 and COP9 signalosome mutant seedlings. This study therefore identifies that DET1-mediated regulation of COP1 stability tunes down HY5 cistrome and avoids hyper-photomorphogenic responses that might compromise plant viability.

plant biology↗

bioRxiv2019

Arabidopsis S2Lb links AtCOMPASS-like and SDG2 activity in histone H3 Lys-4 trimethylation independently from histone H2B monoubiquitination

The functional determinants of histone H3 Lys-4 trimethylation (H3K4me3), their potential dependency on histone H2B monoubiquitination (H2Bub) and their contribution to defining transcriptional regimes are poorly defined in plant systems. Unlike in S. cerevisiae, where a single SET1 protein catalyzes H3 Lys-4 trimethylation as part of COMPASS (COMPlex of proteins ASsociated with Set1), in Arabidopsis thaliana this activity involves multiple histone methyltransferases (HMTs). Among these, the plant-specific SDG2 (SET DOMAIN GROUP2) has a prominent role. We report that SDG2 co-regulates hundreds of genes with SWD2-like b (S2Lb), a plant ortholog of the Swd2 axillary subunit of yeast COMPASS. S2Lb co-purifies with the AtCOMPASS core subunit WDR5 from a high-molecular weight complex, and both S2Lb and SDG2 directly influence H3K4me3 enrichment over highly transcribed genes. S2Lb knockout triggers pleiotropic developmental phenotypes at the vegetative and reproductive stages, including reduced fertility and seed dormancy. Notwithstanding, s2lb seedlings display little transcriptomic defects as compared to the large repertoire of genes targeted by S2Lb, SDG2 or H3 Lys-4 trimethylation, suggesting that H3K4me3 enrichment is important for optimal gene induction during cellular transitions rather than for determining on/off transcriptional status. Moreover, unlike in budding yeast, most of the S2Lb and H3K4me3 genomic distribution does not rely on a trans-histone crosstalk with histone H2B monoubiquitination. Collectively, this study unveils that the evolutionarily conserved COMPASS-like complex has been coopted by the plant-specific SDG2 HMT and mediates H3K4me3 deposition through an H2Bub-independent pathway in Arabidopsis.

plant biology↗

bioRxiv2018

DET1-mediated degradation of a SAGA-like deubiquitination module controls H2Bub homeostasis

DE-ETIOLATED 1 (DET1) is an evolutionarily conserved component of the ubiquitination machinery that mediates the destabilization of key regulators of cell differentiation and proliferation in multicellular organisms. In this study, we provide evidence from Arabidopsis that DET1 is essential for the regulation of histone H2B monoubiquitination (H2Bub) over most genes by controlling the stability of a plant deubiquitination module (DUBm). In contrast with yeast and metazoan DUB modules that are associated with the large SAGA complex, the Arabidopsis DUBm only comprises three proteins (hereafter named SGF11, ENY2 and UBP22) and appears to act independently as a major H2Bub deubiquitinase activity. Our study further unveils that DET1-DDB1-Associated-1 (DDA1) protein interacts with SGF11 in vivo, linking the DET1 complex to light-dependent ubiquitin-mediated proteolytic degradation of the DUBm. Collectively, these findings uncover a signaling path controlling DUBm availability, potentially adjusting H2Bub turnover capacity to the cell transcriptional status.

plant biology↗