Friday May 12, 2023 - Thesis defense - Jean-Philippe Mauxion

Jean-Philippe Mauxion

Team FDFE

Friday, May 12, 2023 - 2:00 pm - Colette and Josy Bové Amphitheater - Campus INRAE Villenave d'Ornon

Abstract :
Tomato fruit pericarp growth can be described as the succession of overlapping and interconnected cellular events with different onsets, different rates and duration in function of the cell layers: anticlinal, periclinal and oblique cell divisions, and isotropic and anisotropic cell expansion. In addition, during cell expansion, a modified cell cycle, the endocycle, during which DNA synthesis occurs independently from mitosis and lead to an increase of DNA content of the cells, takes place. Final fruit size can thus only be achieved through the strict spatial and temporal control and coordination of these events.
In this context, the aim of my PhD was to increase the knowledge on the regulation of cell division and endoreduplication during tomato fruit development. To do so, I used two approaches: reverse and forward genetics approaches. The first approach was based on previous work done on Arabidospis and in the team on known regulators of the cell cycle and the endocycle: the CCS52 proteins. I produced and phenotyped tomato KO-lines by gene editing for the three tomato CCS52 genes. In addition to partial conservation of the function of these genes between the two species, I showed that SlCCS52B was involved in the control of organ shape through the regulation of cell division orientation. Beside the major function described for SlCCS52A in the regulation of endoreduplication, I observed that the tomato mutants seem to show a resumption of cell division with the formation of abnormal nuclei that need to be further studied. SlCCS52A-L seems to be involved in meristem organisation. The second approach aimed at identifying new regulators of endoreduplication by forward genetics. To do so, I made use of an EMS mutant MicroTom collection available in the lab and selected families with an alteration in ploidy and pericarp development and searched for the causal mutation by Bulk-segregant analysis approach. Despite the identification of several candidate loci, the causal mutation(s) still remain(s) to be confirmed.
 
Members of the jury :

• Pr. Esther van der Knaap - Institute of Plant Breeding, Genetics & Genomics, university of Georgia, US, rapportrice.
• Pr. Lieven De Veylder -  VIB-UGent Center for Plant Systems Biology, Ghent, Belgium, rapporteur.
• Dr. David Bouchez - Institut Jean-Pierre Bourgin, INRAE, Versailles, France.
• Pr. Valérie Schurdi-Levraud -  UMR Biologie du Fruit et Pathologie, INRAE -Université de Bordeaux, Bordeaux, France.
• Nathalie Gonzalez -  UMR Biologie du Fruit et Pathologie, INRAE, Bordeaux, France, directrice de thèse.