Fertilization and early seed formation

The double fertilization of flowering plants is a complex process, encompassing multiple steps. From its discovery more than a century ago, many useful descriptive approaches have been employed to better unveil specific steps/mechanisms. More recently, the development of an in vitro assay developed in our laboratory, has allowed a better understanding of this phenomenon. However, in vitro methods may show some limitations. The search for complementary strategies, especially with the search of mutants affected in the fertilization step allowed one to elucidate this critical and unique phenomenon in living organisms. Genes involved in pollen tube guidance or pollen discharge in synergids have been identified, as well as genes exhibiting differential expression in sperm, egg and central cells before and after fertilization. A calcium wave proved to correspond to the first cellular event seen after cytoplasmic fusion in the fertilized egg cell or zygote, which develops into a multi-cellular organism with an elaborate body plan. The development of the fertilized central cell into a nourishing tissue (endosperm) starts with the formation of the coenocyte, a multinuclear single cell unique in the plant kingdom, cellularization occurring later on. The balance of the paternal and maternal genomes, which is under the control of the FIS polycomb group complex, was found to be of the utmost importance for the successful development of the seed. To cite this article: C. Dumas, P. Rogowsky, C. R. Biologies 331 (2008). La double fécondation des plantes à fleurs est un phénomène complexe comportant plusieurs étapes. Depuis sa découverte, il y a plus d'un siècle, plusieurs approches, essentiellement descriptives, ont été successivement développées. Plus récemment, une approche in vitro a permis de mieux comprendre ce phénomène. Néanmoins, de telles méthodes in vitro peuvent présenter des limitations. La recherche de nouvelles stratégies, en particulier l'étude de mutants affectés dans la fécondation, est utile car elle permet de mieux comprendre cette étape critique et unique des organismes vivants. Ces nouvelles approches ont permis la découverte de gènes impliqués dans l'attraction du tube pollinique ou la décharge du pollen dans les synergides ainsi que la caractérisation de gènes exprimés de manière différentielle entre le gamète mâle, l'oosphère et la cellule centrale avant ou après fécondation. Une vague de calcium est le premier évènement cellulaire documenté après