Biology subjects

Louveaux, M.

Publications and source records attributed to Louveaux, M..

5 recordsLinked to original sources

bioRxiv2022

Progressive maturation of the root apical meristem in Arabidopsis thaliana lateral roots

Meristems are stem cells niches that support the formation of all plant organs and are either set during embryogenesis and maintained throughout the plant life or specified de novo, post-embryonically. The embryo-derived root apical meristem is organized around a group of infrequently dividing cells, the quiescent centre, that maintains the stem cells, organizes growth along two axes and owing to its resistance to 3ic stress can replace damaged stem cells. In most cases, lateral roots post-embryonically branch off the primary and establish a new root meristem which organization is identical to the primary root one. The cellular and molecular processes underpinning the emergence of new stem cell niches are not well known. Here, we characterize the de novo establishment of the root apical meristem in lateral roots. While the position of the new stem cell niche is set early during morphogenesis, its cellular layout, unique gene expression profile and mitotic quiescence are only acquired after emergence concomitant to the establishment of two diverging growth axis. Our results show that the intertwined attributes of the mature root stem cell niche are progressively acquired during lateral root formation, and support a model in which the position of the stem cell niche emerges from the establishment of diverging growth axis. HighlightAnalyze of the ontogeny of the quiescent center during lateral root ontogeny reveal its late formation and supports that its emergence results from the establishment of two diverging growth axis.

plant biology↗

bioRxiv2020

Integration of Cell Growth and Asymmetric Division During Lateral Root Initiation In Arabidopsis thaliana

Lateral root formation determines to a large extent the ability of plants to forage their environment and thus their growth. In Arabidopsis thaliana and other angiosperms, lateral root initiation requires radial cell expansion and several rounds of anticlinal cell divisions that give rise to a central core of small pericycle cells, which express different markers than the larger surrounding cells. These small central cells then switch their plane of divisions to periclinal, and give rise to seemingly morphologically similar daughter cells that have different identities and establish the different cell types of the new root. Although the execution of these two types of divisions is tightly regulated and essential for the correct development of the lateral root, we know little about their geometrical features. Here we analyse a four-dimensional reconstruction of the first stages of lateral root formation and analyze the geometric features of the anticlinal and periclinal divisions. We identify that the periclinal divisions of the small central cells are morphologically dissimilar and asymmetric. We show that mother cell volume is different when looking at anticlinal versus periclinal divisions and the repeated anticlinal divisions do not lead to reduction in cell volume although cells are shorter. Finally, we show that cells undergoing a periclinal division are characterized by a strong cell expansion. Our results indicate that cells integrate growth and division to precisely partition their volume upon division during the first two stages of lateral root formation.

plant biology↗

bioRxiv2020

Direct tracking of single proviruses reveals HIV-1/LEDGF complexes excluded from virus-induced membraneless organelles

HIV integration occurs in chromatin sites that favor the release of high levels of viral progeny, alternatively the virus is also able to discreetly coexist with the host. The viral infection perturbs the cellular environment inducing the remodeling of the nuclear landscape. Indeed, HIV-1 triggers the nuclear clustering of the host factor CPSF6, but the underlying mechanism is poorly understood. Our data indicate that HIV usurps a recently discovered biological phenomenon, called liquid-liquid phase separation (LLPS), to hijack the host cell. We observed CPSF6 clusters as part of HIV-induced membraneless organelles (HIV-1 MLOs) in macrophages, which are one of the main HIV target cells. We describe that HIV-1 MLOs follow phase separation rules and represent functional biomolecular condensates. We highlight HIV-1 MLOs as hubs of nuclear reverse transcription, while the double stranded viral DNA, once formed, rapidly migrates outside these structures. Transcription-competent proviruses localize outside, but near HIV-1 MLOs, in LEDGF-abundant regions, known to be active chromatin sites. Therefore, HIV-1 MLOs orchestrate viral events prior to the integration step and create a favorable environment for the viral replication. This study uncovers single functional host-viral complexes in their nuclear landscape, which is markedly restructured by HIV-1.

microbiology↗

bioRxiv2020

Accurate And Versatile 3D Segmentation Of Plant Tissues At Cellular Resolution

Quantitative analysis of plant and animal morphogenesis requires accurate segmentation of individual cells in volumetric images of growing organs. In the last years, deep learning has provided robust automated algorithms that approach human performance, with applications to bio-image analysis now starting to emerge. Here, we present PlantSeg, a pipeline for volumetric segmentation of plant tissues into cells. PlantSeg employs a convolutional neural network to predict cell boundaries and graph partitioning to segment cells based on the neural network predictions. PlantSeg was trained on fixed and live plant organs imaged with confocal and light sheet microscopes. PlantSeg delivers accurate results and generalizes well across different tissues, scales, and acquisition settings. We present results of PlantSeg applications in diverse developmental contexts. PlantSeg is free and open-source, with both a command line and a user-friendly graphical interface.

plant biology↗

bioRxiv2019

Cytoskeleton dynamics control early events of lateral root initiation in Arabidopsis

How plant cells re-establish differential growth to initiate organs is poorly understood. Morphogenesis of lateral roots relies on the tightly controlled radial expansion and asymmetric division of founder cells. The cellular mechanisms that license and ensure these features are unknown. Here, we quantitatively analyse F-actin and microtubule dynamics during LR initiation. Using mutants, pharmacological and tissue-specific genetic perturbations, we show that dynamic reorganisation of both microtubule and F-actin networks is required for the asymmetric expansion of the founder cells. This cytoskeleton remodelling intertwine with auxin signalling in the pericycle and endodermis in order for founder cells to acquire a basic polarity required for initiating LR development. Our results reveal the conservation of cell remodelling and polarisation strategies between the Arabidopsis zygote and lateral root founder cells. We propose that coordinated, auxin-driven reorganisation of the cytoskeleton licenses asymmetric cell growth and divisions during embryonic and post-embryonic organogenesis. HIGHLIGHTSO_LIFailure for lateral root founder cells to undergo asymmetric radial expansion before division, leads to aberrant organ formation. C_LIO_LICortical microtubules arrays reorganise to facilitate this asymmetric expansion and F-actin the asymmetric division. C_LIO_LICytoskeletal reorganisation depends on auxin signalling. C_LIO_LINew genetic tools allow to perturb microtubules or actin in an inducible and cell-type specific manner. C_LI

plant biology↗