3D architecture of the ovule during MMC differentiation in Paspalum rufum.

DELGADO LUCIANA; INES, OUEDRAOGO; BAROUX, CELIA; AUTRAN, DAPHNÉ

Rosario

Congreso; IV International Congress on Apomixis Research; 2023

IICAR-CONICET, CERZOS-CONICET, IBONE-CONICET

During the early stages of sexual female sporogenesis development, a single sub-epidermal cell from the nucella differentiates into the Megaspore Mother Cell (MMC), marking the somatic to reproductive transition in higher plants. Although the number of MMCs varies by species and genetic background, in most cases, only a single MMC per ovule enters meiosis to form the embryo sac. In Arabidopsis, the restriction to a single MMC per ovule, or MMC singleness, is determined by ovule geometry. Alternatively, in aposporous apomictic plants, additional enlarged cells, called Aposporous Initials surround the MMC and bypassing meiosis produce unreduced aposporous embryo sacs. Paspalum rufum is an aposporic grass organized in agamic complexes, where diploid cytotype reproduce by sexuality and tetraploid by facultative aposporous apomictic. Both reproductive pathways proceed within the same ovule during sporogenesis and megagametogenesis. Moreover, some diploid genotypes are able to produce aposporous embryo sacs in a relative high proportion and more than one reduced embryo sacs were also detected within the same ovule. Despite the potential for apomixis, sexuality prevails in diploids, and apomixis in tetraploids, which is related to heterochrony of ovule growth and reproductive development between both ploidy levels. The plasticity observed in Paspalum rufum in both ovule growth and reproductive developmental pathways offers an interesting model to study the contribution of the growth parameters at cellular level in the somatic to reproductive transition within the ovule primordia. We generated a collection of three-dimensional images of the ovule primordial spanning MMC differentiation, of diploid and tetraploid sexual and aposporic genotypes of Paspalum rufum. Our first analysis allowed us to obtain cellular morphological descriptors of MMC and its neighboring cellular network, suggesting a pool of candidate archesporial cells at early stages, canalized to a single enlarged MMC cell at late stage. Comparative analysis of the whole ovule cellular architecture throughout development between different reproductive behaviour and ploidy levels will allow us to analyse the MMC singleness in such different contexts, and to understand the sexual to aposporic transitions during the onset of Aposporous Initials.