Biophysical and cellular mechanisms of tip-growth in the brown alga Ectocarpus sp. Herve Rabille To cite this version: Herve Rabille. Biophysical and cellular mechanisms of tip-growth in the brown alga Ectocarpus sp.. Cellular Biology. Sorbonne Université, 2018. English. NNT : 2018SORUS597. tel-02489811 HAL Id: tel-02489811 https://tel.archives-ouvertes.fr/tel-02489811 Submitted on 24 Feb 2020 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. Sorbonne Université Ecole doctorale 515 Complexité du Vivant UMR 8227 (SU – CNRS) Laboratoire de Biologie Intégrative des Modèles Marins / Equipe de recherche « Morphogenesis of Macroalgae » Biophysical and cellular mechanisms of tip-growth in the brown alga Ectocarpus sp. Par Hervé Rabillé Thèse de doctorat de Biologie Dirigée par Dr. Bénédicte Charrier Présentée et soutenue publiquement le 3 décembre 2018 Devant un jury composé de : M. Arezki Boudaoud, Professeur de l’ENS de Lyon, France : Rapporteur Mme. Siobhan Braybrook, Project Investigator at the University California Los Angeles, USA : Rapporteuse M. Benedikt Kost, Professeur de l’Université Friedrich Alexander Universität, Erlangen, Allemagne : Examinateur M. Bernard Kloareg, Professeur de Sorbonne Université de Paris, France : Examinateur Mme Bénédicte Charrier, Directrice de Recherche CNRS : Directrice de thèse Rabillé Hervé – Thèse de doctorat – 2018 Biophysical and cellular mechanisms of tip-growth in Ectocarpus Sorbonne Université Ecole doctorale 515 Complexité du Vivant UMR 8227 (SU – CNRS) Laboratoire de Biologie Intégrative des Modèles Marins / Equipe de recherche « Morphogenesis of Macroalgae » Biophysical and cellular mechanisms of tip-growth in the brown alga Ectocarpus sp. Par Hervé Rabillé Thèse de doctorat de Biologie Dirigée par Dr. Bénédicte Charrier Présentée et soutenue publiquement le 3 décembre 2018 Devant un jury composé de : M. Arezki Boudaoud, Professeur de l’ENS de Lyon, France : Rapporteur Mme. Siobhan Braybrook, Project Investigator at the University California Los Angeles, USA : Rapporteuse M. Benedikt Kost, Professeur de l’Université Friedrich Alexander Universität, Erlangen, Allemagne : Examinateur M. Bernard Kloareg, Professeur de Sorbonne Université de Paris, France : Examinateur Mme Bénédicte Charrier, Directrice de Recherche CNRS : Directrice de thèse 1 Biophysical and cellular mechanisms of tip-growth in Ectocarpus 2 Biophysical and cellular mechanisms of tip-growth in Ectocarpus Preamble Contribution This thesis project is by no means the only product of my own work, but is instead the fruit of the collective work of many people. The contribution of each is detailed below. At first, the project has involved the effort of all the members of the Morphogenesis of MacroAlgae research team. Dr Bénédicte Charrier, researcher in plant biology, performed a substantial part of the cytology experiments and data analysis. Dr Bernard Billoud, lecturer in bioinformatics, contributed to the analysis of some quantitative data and carried out all the computational work related to the mechanical modelling of Ectocarpus tip-growth. Élodie Rolland, research technician in tissue culture, performed most of the algae cultivation tasks, especially the preparation of the parthenosporophytes of Ectocarpus grown on glass coverslips, which were essential for most of the experiments. The staining of the actin cytoskeleton using the phalloidin-based probe has been performed in collaboration with Pr. Christos Katsaros and his PhD student Maria Koutalianou, both from the National and Kapodistrian University of Athens (Greece). Actin and tubulin immunolocalisation experiments have been carried out with Dr. Adeel Nasir (Friedrich Alexander Universität, Erlangen-Nurnberg, Germany), who supplied us with an alternative protocol for cytoskeleton staining during a short visit. All the observations of cell ultrastructure by Transmission Electronic Microscopy (TEM) have been conducted by Dr. Sophie Le Panse, from the “MerImage” microscopy plateform at the Roscoff Marine Biology Station. The AFM data that are briefly presented and discussed in this report have been acquired by Benoit Tesson (Scripps Institution of Oceanography, University of California, San Diego, USA). The identification of the causal mutation in the mutant étoile (etl) and the bioinformatic analysis (with the help of B. Billoud) of the candidate ETOILE gene which is briefly discussed in this report, is mostly the work of Zofia Nehr (former PhD student in the team). I performed the final completion of her substantial work with the help of the L2 student Quentin Rochas, whom I supervised. Finally, the results presented on the effect of drugs depolymerizing the cytoskeleton on the growth and morphogenesis of the apical cell were from time-lapse pictures of Ectocarpus filaments grown by Carole Duchêne, a former L3 internship in our team. Articles The Part 1 (Introduction section) of the report contains a large chapter reviewing the biomechanical models of tip-growth across the tree of life. It will be submitted as a review for an annual series or a book (Rabillé & Charrier, in preparation). The Part 1 also comprises an Opinion paper discussing the extent to which the cell wall composition and its intrinsic mechanics impact growth (Charrier, Rabillé & Billoud, in press in Trends in Plant Science). The Part 2 deals with the biomechanics of tip-growth and of the cell wall. It contains two Original Research papers. The first article (Part 2.1) presents a visco-elastic model accounting for the tip growth in Ectocarpus, highlighting the role of the cell wall thickness 3 Biophysical and cellular mechanisms of tip-growth in Ectocarpus (Rabillé et al., in revision in PLoS Biology). The second one (Part 2.2) reports the role of alginates in the mechanics of the cell wall along the filament of Ectocarpus (Rabillé et al., in preparation). 4 Biophysical and cellular mechanisms of tip-growth in Ectocarpus Acknowledgements First I must thank the two organisms that have funded my PhD: The Presidency of the former Université Pierre and Marie Curie (now fused with Sorbonne Université) and the Brittany Region. I am also indebted to the Phycomorph Network (EC funded COST Action FA1406) for having funding my Short-Term Scientific Mission from the 12th to the 29th of October, 2016, in the laboratory of Pr. Christos Katsaros (see below). I thank warmly Dr Bénédicte Charrier, head of the Morphogenesis of MacroAlgae (MMA) team and my PhD supervisor, for having given me the opportunity to do work on such an exciting research project, at the very forefront of the current knowledge in cellular and developmental biology. Thank also you a lot for all the time you have dedicated to supervising my thesis, for all the (often very long) theoretical discussions about the mechanisms of cell growth, and especially on wall expansion mechanisms, the very hot topic that repeatedly came at the center of our thoughts in the course of these three years. Also, thank you for founding the very last weeks of this thesis project. In the same vein, I have to thank you a lot, Dr Bernard Billoud, for your dedication into the project, and for the HUGE work for the numerical modelling of Ectocarpus tip-growth. Thank you also for, again, all the theoretical discussions mentioned above, and for you many informed, enlightened, and often stated loud and clear, points of view on the numerous hot technical and theoretical issues this research project has given rise to. More generally, I would like to tell all my gratitude to both B. Charrier and B. Billoud, for the overwhelming work that was the redaction and formatting of the two original papers which drafts are included in this report, in which I have only played a small part. I also would like to thank Dr Catherine Boyen for having funded one extra month and a half of my thesis, that have allowed me to have time to write my report (extra time that I have largely abused). I would also like to thanks all the member of my thesis committee, for their GREAT patience and indulgence (my apologies, again, for the almost 2 hours’ lateness at the second meeting, and my complete lack of professionalism), for their interest in the project and their kind pieces of advice. So thanks to Pr Bruno De Reviers, Dr Hayat Bouteau, Dr Thierry Comtet. Thank also to Dr Arezki Boudaoud and Dr. B. Billoud for attending the first meeting in February 2017. I thank also all the members of my thesis comitee, that have kindly accepted to attend and evaluate my future thesis defence, that is to take place on the 3rd of December 2018. So thank you Dr Siobhan Braybrook, Dr Arezki Boudaoud, Dr Bernard Kloareg and Dr Benedikt Kost. Many thanks especially for two former for tackling the task of evaluating this huge report. Here and now, I would like to thanks all the other people that have got involved in the thesis project, and without whom nothing, or so few, would have been possible. First I would like to thanks Élodie Rolland, research technician in the team, for preparing loads of Ectocarpus cultures necessary