Biology subjects

Lebecq, A.

Publications and source records attributed to Lebecq, A..

5 recordsLinked to original sources

bioRxiv2026

A developmentally scheduled inhibitory polarity circuit centers the stomatal pore

Symmetry in living systems often arises from coordinated asymmetries at smaller scales. The guard cells of stomata--bilaterally symmetric epidermal valves that mediate plant-atmosphere gas exchange--show coordinated asymmetries in pore placement and wall modification. Stomatal form and function are deeply conserved, yet molecular mechanisms defining coordinated cellular asymmetry are unknown. Here we show that pore position arises from a combination of pole avoidance and gradient centering in the membranes and wall dividing sister guard cells. Boundaries are established by spatiotemporal restriction of the receptor-like kinase MUSTACHES (MUS), which directs the disordered polarity protein OCTOPUS-LIKE2 (OPL2) to pore-forming regions. OPL2 peaks correspond to a focus of microtubules, and, from this position, the pore emerges. Experimental rewiring of the MUS-OPL2 polarity module profoundly impacts stomatal morphogenesis, eliminating, shifting, or even redirecting the pore to the opposite wall. These findings reveal a stomata-specific integration and elaboration of core polarity and centering programs, and challenge previous models of stomatal morphogenesis.

developmental biology↗

bioRxiv2022

The phosphoinositide signature guides the final step of plant cytokinesis

Plant cytokinesis, which fundamentally differs from that in animals, involves de novo assembly of a plasma membrane precursor named the cell plate. How the transition from the cell plate to a plasma membrane occurs at the end of the plant cytokinesis remains poorly understood. Here, we describe with unprecedented spatiotemporal precision, the acquisition of plasma membrane identity upon cytokinesis through the lateral patterning of phosphatidylinositol 4,5-bisphosphate PI(4,5)P2 at the newly formed cell plate membrane. We show that during late cytokinesis, opposing polarity domains are formed along the cell plate. Exclusion of PI(4,5)P2 from the leading edge of the cell plate is controlled by SAC9, a putative phosphoinositide phosphatase. SAC9 colocalizes with MAP65-3, a key regulator of the cytokinesis, at the cell plate leading zone and regulates its function. In the sac9-3 mutant, the polar distribution of PI(4,5)P2 at the cell plate is altered, leading to de-novo recruitment of the cytokinesis apparatus and to formation of an additional, ectopic cell plate insertion site. We proposed that PI(4,5)P2 acts as a polar cue to spatially separate the expansion and maturation domains of the forming cell plate during the final steps of cytokinesis. One Sentence SummaryThe phosphoinositide PI(4,5)P2 acts as an hallmark to guide the final step of plant cell division.

cell biology↗

bioRxiv2021

The Arabidopsis SAC9 Enzyme defines a cortical population of early endosomes and restricts PI(4,5)P2 to the Plasma Membrane

Membrane lipids, and especially phosphoinositides, are differentially enriched within the eukaryotic endomembrane system. This generates a landmark code by modulating the properties of each membrane. Phosphatidylinositol 4,5-bisphosphate [PI(4,5)P2] specifically accumulates at the plasma membrane in yeast, animal and plant cells, where it regulates a wide range of cellular processes including endocytic trafficking. However, the functional consequences of mispatterning PI(4,5)P2 in plants are unknown. Here, we functionally characterized the putative phosphoinositide phosphatase SUPPRESSOR OF ACTIN9 (SAC9) in Arabidopsis thaliana (Arabidopsis). We found that SAC9 depletion led to the ectopic localization of PI(4,5)P2 on cortical intracellular compartments, which depends on PI4P and PI(4,5)P2 production at the plasma membrane. SAC9 localizes to a subpopulation of trans-Golgi Network/early endosomes that are enriched in a region close to the cell cortex and that are coated with clathrin. Furthermore, it interacts and colocalizes with Src Homology 3 Domain Protein 2 (SH3P2), a protein involved in endocytic trafficking. In the absence of SAC9, SH3P2 localization is altered and the clathrin-mediated endocytosis rate is reduced. Together, our results highlight the importance of restricting PI(4,5)P2 at the plasma membrane and illustrate that one of the consequence of PI(4,5)P2 misspatterning in plants is to impact the endocytic trafficking. One-sentence summarySAC9 prevents the accumulation of PI(4,5)P2 in intracellular compartments, thereby contributing to clathrin-mediated endocytosis at the plasma membrane and regulating the cortical localization of its protein partner SH3P2.

plant biology↗

bioRxiv2021

Dynamic Apical-Basal Enrichment of the F-Actin during Cytokinesis in Arabidopsis Cells Embedded in Their Tissues

During the life cycle of any multicellular organism, cell division contributes to the proliferation of the cell in the tissues as well as the generation of specialized cells, both necessary to form a functional organism. Therefore, the mechanisms of cell division need to be tightly regulated, as malfunctions in their control can lead to tumor formation or developmental defects. This is particularly true in land plants, where cells cannot relocate and therefore cytokinesis is key for morphogenesis. In the green lineage, cell division is executed in radically different manners than animals, with the appearance of new structures (the preprophase band (PPB), cytokinetic the cell plate and phragmoplast), and the disappearance of ancestral mechanisms (cleavage, centrosomes). While F-actin and microtubules closely co-exist to allow the orientation and the progression of the plant cell division, recent studies mainly focused on the microtubules involvement in this key process. Here, we used our recently developed root tracking system to follow actin dynamics in dividing Arabidopsis meristematic root cells. In this study, we imaged in time and space the fluorescent-tagged F-actin reporter Lifeact together with cell division markers in dividing cells embedded in their tissues. In addition to the F-actin accumulations in the phragmoplasts, we observed and quantified a dynamic apical-basal enrichment of the F-actin during cytokinesis. The role and the possible actors responsible for F-actin dynamics during cytokinesis are discussed.

cell biology↗

bioRxiv2020

iDePP: a genetically encoded system for the inducible depletion of PI(4,5)P2 in Arabidopsis thaliana.

Phosphatidylinositol 4,5-bisphosphate [PI(4,5)P2] is a low abundant lipid present at the plasma membrane of eukaryotic cells. Extensive studies in animal cells revealed the pleiotropic functions of PI(4,5)P2. In plant cells, PI(4,5)P2 is involved in various cellular processes including the regulation of cell polarity and tip growth, clathrin-mediated endocytosis, polar auxin transport, actin dynamics or membrane-contact sites. To date, most studies investigating the role of PI(4,5)P2 in plants have relied on mutants lacking enzymes responsible for PI(4,5)P2 synthesis and degradation. However, such genetic perturbations only allow steady-state analysis of plants undergoing their life cycle in PI(4,5)P2 deficient conditions and the corresponding mutants are likely to induce a range of non-causal (untargeted) effects driven by compensatory mechanisms. In addition, there are no small molecule inhibitors that are available in plants to specifically block the production of this lipid. Thus, there is currently no system to fine tune PI(4,5)P2 content in plant cells. Here we report a genetically encoded and inducible synthetic system, iDePP (Inducible Depletion of PI(4,5)P2 in Plants), that efficiently removes PI(4,5)P2 from the plasma membrane in different organs of Arabidopsis thaliana, including root meristem, root hair and shoot apical meristem. We show that iDePP allows the inducible depletion of PI(4,5)P2 in less than three hours. Using this strategy, we reveal that PI(4,5)P2 is critical for cortical microtubule organization. Together, we propose that iDePP is a simple and efficient genetic tool to test the importance of PI(4,5)P2 in given cellular or developmental responses but also to evaluate the importance of this lipid in protein localization. Research OrganismA. thaliana

plant biology↗