Biology subjects

Lebrun, R.

Publications and source records attributed to Lebrun, R..

7 recordsLinked to original sources

bioRxiv2025

Bacterial Hsp90 promotes virulence factor production through maintenance of NRPS megaenzymes

Pathogenic bacteria produce virulence factors critical to host infection. Here, we demonstrate the crucial role of the bacterial Hsp90 chaperone in the production of two major virulence factors, the colibactin genotoxin in Escherichia coli and the pyoverdine siderophore in Pseudomonas aeruginosa. Colibactin, a hybrid polyketide/non-ribosomal peptide (PK-NRP), and pyoverdine, a non-ribosomal peptide (NRP), are metabolites produced by complex biosynthetic pathways involving large cytoplasmic enzymes called megasynthases. Using comparative proteomics, we found that megasynthase abundance was markedly reduced in hsp90 deletion mutants of E. coli and P. aeruginosa compared to wild-type strains. This reduction was independent of transcriptional or translational regulation. We further revealed an interplay between Hsp90 and the HslUV protease in controlling megasynthase levels. Remarkably, we found that Hsp90 stabilizes additional NRP and PK-NRP megasynthases, suggesting a general role for Hsp90 as a chaperone of these enzymes. These findings open new avenues for enhancing the biosynthesis of complex metabolites for biotechnological applications through proteostasis modulation, and may also have implications for combating bacterial infections.

microbiology↗

bioRxiv2025

Thriving Across Depths: How Blue Light Shapes a Large PSI Supercomplex and Specic Photosynthetic Traits in the seagrass Posidonia oceanica.

Photosynthetic organisms rely on finely tuned mechanisms to optimize photosynthesis under different light conditions. While these processes are well-characterized in land plants, the adaptive strategies of marine plants remain largely unexplored. The Mediterranean seagrass Posidonia oceanica (Alismatales), a key ecosystem engineer thriving from the surface up to 40m depth and one of the largest long-term blue carbon sinks in coastal environments. Here, we investigate how P. oceanica adjusts its photosynthetic apparatus in response to varying light spectra encountered at different seawater depths. Contrary to land plants, P. oceanica maintains a relatively high PSI/PSII ratio and a high content of the major light-harvesting complex II (LHCII), regardless of depth. Notably, the antenna size of the photosystems remains stable across depths, although we document significant depth-dependent reorganization of the thylakoid membrane ultrastructure. Moreover, we identify a novel large PSI-LHCII supercomplex (L-PSI-LHCII) in P. oceanica, characterized by additional Lhca proteins, reduced red-shifted absorption, and increased chlorophyll b content. Ultrafast spectroscopy reveals the distinct energy transfer dynamics within this complex. The presence of a similar supercomplex in other marine plants, such as Zostera marina, suggests a conserved adaptive strategy among seagrasses.

plant biology↗

bioRxiv2025

CP12 controls ribulose 1,5 bisphosphate recycling and carbon acquisition in Chlamydomonas reinhardtii

The small chloroplastic protein CP12 has multiple functions, including the regulation of enzymes in the Calvin-Benson-Bassham cycle. Here, we investigated its role in the acclimation of Chlamydomonas reinhardtii to varying CO2 availability. This alga has a CO2 concentrating mechanism that increases the supply of CO2 to ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) and involves hallmarks such as HCO3- transporters and carbonic anhydrases as well as the condensation of RuBisCO within the pyrenoid via its interaction with a scaffold protein named Essential Pyrenoid Component 1 (EPYC1). We showed that compared to the wild type, at high CO2, C. reinhardtii CP12 deletion mutants, or partially complemented mutants, have less phosphoribulokinase and ribulose-1,5-bisphosphate (RuBP) indicating that the regeneration of RuBP is regulated by CP12. In the absence of CP12, the expected relocation of RuBisCO towards the pyrenoid was not observed upon transition from high to very low CO2, contrary to WT cells. The CP12 deletion mutants are a unique example where the induction of CO2 concentrating mechanism hallmarks at very low CO2 was not accompanied by RuBisCO relocation. Altogether, these results suggest that CP12 contributes to the coordination between RuBP regeneration, RuBisCO location and CO2 acquisition. HighlightCP12 regulates phosphoribulokinase amount and its product RuBP. The CP12 deletion mutants are unique example where the RuBisCO location was not correlated with the induction of CO2 concentration mechanism. This reveals a novel link between Calvin-Benson-Bassham cycle regulation and CO2 concentrating mechanisms in Chlamydomonas reinhardtii. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=115 SRC="FIGDIR/small/659560v1_ufig1.gif" ALT="Figure 1"> View larger version (39K): org.highwire.dtl.DTLVardef@1cdadb2org.highwire.dtl.DTLVardef@46ae27org.highwire.dtl.DTLVardef@538295org.highwire.dtl.DTLVardef@a214c7_HPS_FORMAT_FIGEXP M_FIG C_FIG

biochemistry↗

bioRxiv2023

Post-translational regulation of photosynthetic activity via the TOR kinase in plants.

Chloroplasts are the powerhouse of the plant cell, yet they are resource-intensive and will cause photooxidative damage if their activity overshoots the demands of growth. The adjustment of chloroplast activity to match growth is therefore vital for stress acclimation. Here we identify a novel post-translational mechanism linking the conserved eukaryotic TOR kinase that promotes growth and the guanosine tetraphosphate (ppGpp) signaling pathway of prokaryotic origin that regulates chloroplast activity, and photosynthesis in particular. We show that RelA SpoT Homologue 3 (RSH3), a nuclear-encoded chloroplastic enzyme responsible for ppGpp biosynthesis, interacts directly with the TOR complex via a plant-specific N-terminal region (NTR) which is hyper-phosphorylated in a TOR-dependent manner. Downregulation of TOR activity reduces NTR phosphorylation, enhances ppGpp synthesis by RSH3, and causes a ppGpp-dependent decrease in photosynthetic capacity. Altogether we demonstrate that the TOR-RSH3 signaling axis is a novel and direct post-translational mechanism that allows chloroplast activity to be matched with plant growth, setting a new precedent for the regulation of organellar function by TOR. One sentence summaryThe TOR kinase post-translationally controls guanosine tetraphosphate signaling to regulate plant photosynthetic activity.

plant biology↗

bioRxiv2023

Proteomic analyses of the Arabidopsis cap-binding complex define core set and TOR-dependent protein components

The eukaryotic cap-binding complex (CBC) is a hub for regulations affecting mRNA behaviour including translation, degradation and storage. Beside the core eukaryotic translation initiation factors, other proteins, many of which are yet unknown, are thought to interact stably or transiently with the CBC depending on cell status. The prototype of these regulators is the animal eIF4E binding protein (4E-BP), a direct target of the TOR (Target of Rapamycin) kinase that competes with the cap-binding protein eIF4E, thus repressing translation. In plants, no functional homologs of 4E-BP have so far been characterized. In this work we performed several deep proteomic analyses of the Arabidopsis CBC after cap-affinity purification from wild-type plants. We also investigated the CBC in eIF4E mutant plants, Arabidopsis lines with lower TOR activity, or during infection with eIF4E-dependent potyviruses, conditions which are all affecting translation at the initiation level. These analyses allowed us to define a limited core set of CBC components, which were detected in all samples. Interestingly, we identified proteins, like AGO1 or VCS, which were always detected in conditions where either TOR or mRNA translation were reduced. Meta-analysis of these data revealed several new plant interactors of the CBC, potentially defining pathways related to mRNA stability and degradation, metabolism and viral life cycle. A search for eIF4E binding motifs identified several new potential 4E-BP relatives in plants.

plant biology↗

bioRxiv2022

Natural variability in bee brain size and symmetry revealed by micro-CT imaging and deep learning

Analysing large numbers of brain samples can reveal minor, but statistically and biologically relevant variations in brain morphology that provide critical insights into animal behaviour, ecology and evolution. So far, however, such analyses have required extensive manual effort, which considerably limits the scope for comparative research. Here we used micro-CT imaging and deep learning to perform automated analyses of 3D image data from 187 honey bee and bumblebee brains. We revealed strong inter-individual variations in total brain size that are consistent across colonies and species, and may underpin behavioural variability central to complex social organisations. In addition, the bumblebee dataset showed a significant level of lateralization in optic and antennal lobes, providing a potential explanation for reported variations in visual and olfactory learning. Our fast, robust and user-friendly approach holds considerable promises for carrying out large-scale quantitative neuroanatomical comparisons across a wider range of animals. Ultimately, this will help address fundamental unresolved questions related to the evolution of animal brains and cognition. Author SummaryBees, despite their small brains, possess a rich behavioural repertoire and show significant variations among individuals. In social bees this variability is key to the division of labour that maintains their complex social organizations, and has been linked to the maturation of specific brain areas as a result of development and foraging experience. This makes bees an ideal model for understanding insect cognitive functions and the neural mechanisms that underlie them. However, due to the scarcity of comparative data, the relationship between brain neuro-architecture and behavioural variance remains unclear. To address this problem, we developed an AI-based approach for automated analysis of brain images and analysed an unprecedentedly large dataset of honey bee and bumblebee brains. Through this process, we were able to identify previously undescribed anatomical features that correlate with known behaviours, supporting recent evidence of lateralized behaviour in foraging and pollination. Our method is open-source, easily accessible online, user-friendly, fast, accurate, and robust to different species, enabling large-scale comparative analyses across the animal kingdom. This includes investigating the impact of external stressors such as environmental pollution and climate change on cognitive development, helping us understand the mechanisms underlying the cognitive abilities of animals and the implications for their survival and adaptation.

animal behavior and cognition↗

bioRxiv2020

ppGpp influences protein protection, growth and photosynthesis in Phaeodactylum tricornutum

O_LIChloroplasts retain elements of a bacterial stress response pathway that is mediated by the signalling nucleotides guanosine penta- and tetraphosphate, or (p)ppGpp. In the model flowering plant Arabidopsis, ppGpp acts as a potent regulator of plastid gene expression and influences photosynthesis, plant growth and development. However, little is known about ppGpp metabolism or its evolution in other photosynthetic eukaryotes. C_LIO_LIHere, we studied the function of ppGpp in the diatom P. tricornutum using transgenic lines containing an inducible system for ppGpp accumulation. We used these lines to investigate the effects of ppGpp on growth, photosynthesis, lipid metabolism and protein expression. C_LIO_LIWe demonstrate that ppGpp accumulation reduces photosynthetic capacity and promotes a quiescent-like state with reduced proliferation and ageing. Strikingly, using non-targeted proteomics, we discovered that ppGpp accumulation also leads to the coordinated upregulation of a protein protection response in multiple cellular compartments. C_LIO_LIOur findings highlight the importance of ppGpp as a fundamental regulator of chloroplast function across different domains of life, and lead to new questions about the molecular mechanisms and roles of (p)ppGpp signalling in photosynthetic eukaryotes. C_LI

plant biology↗