Résumé
Natural species of Paspalum are organised in agamic complexes, in which different ploidy levels are linked to sexual or apomictic reproduction. In apomictic aposporic plants, additional enlarged cells, called AposporousInitials (AIs), surround the sexual Megaspore Mother Cell (MMC) and produce aposporic embryo sacs. Although apomictic, polyploid plants are mostly facultative, and in addition, some sexual diploid genotypes can reproduceby apomixis. The same genotype may display significant developmental plasticity during megasporogenesis and megagametogenesis, and ovules can generate both sexual and/or apomictic pathways in different proportionsdepending on environmental conditions. Furthermore, developmental plasticity is also present in ovules of sexual plants,such as Arabidopsis and Maize, where a pool of precursor cells enters the MMC differentiation trajectory up to variable steps,depending on genotypes and species. As development proceeds, mostly a single MMC per ovule enters meiosis. In addition,in both sexual and apomictic systems, the formation of reproductive cells is strongly linked to ovule growth andgeometry. Here, we focus on the early steps of female reproductive development and ask, at a cellular level, whetherdifferential geometry and topology in the ovule primordium influence AI and MMC differentiation, conditioningthe shift between apomixis and sexuality. For this purpose, we generated a collection of 136 3D images of diploid/tetraploidand sexual/apomictic genotypes of Paspalum rufum ovules, spanning MMC differentiation. We analyse 3D morphological and topologicaldescriptors at both cellular and organ levels. The first observations indicate a pool of candidate archesporialcells at early stages, canalised later to a single enlarged MMC, associated also with higher network centralitymeasures. Moreover, ovule growth and differentiation of the reproductive cells appear differentially coordinatedaccording to ploidy levels. A comprehensive analysis of MMC and AI initiation is underway to understand thedevelopmental plasticity associated with sexual to aposporic transitions in Paspalum.