THE FEMALE GAMETOPHYTE: DEVELOPMENT AND FUNCTION

The plant life cycle alternates the diploid sporophyte and the haploid gametophyte. The female gametophyte of flowering plants develops within the ovule, a specialized structure within the ovary, which gives rise to the seed after fertilization. Sexual reproduction in plants entails a series of developmental steps that culminate in the formation of the seed. The developing ovule protects the haploid female gametophyte, which is formed as the result of the megasporogenesis and megagametogenesis. Inside the female gametophyte, the two female gametic cells, the central and the egg cells, upon fertilization give rise to the seed endosperm and embryo respectively. During my PhD, I dissect the genetic and molecular networks controlling female gametophyte formation and differentiation. I employed a yeast one-hybrid approach to identify EC1.1 regulators; the EC1 genes are specifically expressed in the female gamete and they are required for gamete fusion, therefore they are good candidates for clarify how gamete differentiation occurs in Arabidopsis thaliana. Among the transcription factors isolated, we focused on SUPPRESSOR OF FRIGIDA4 (SUF4). In vivo and in vitro evidences support SUF4 capacity to regulate AtEC1.1, furthermore suf4 mutants show also a mild ec1 phenotype. Plant can produce progeny without sexual reproduction. One example is apomixis, where meiosis and fertilization of the egg by male gametes are by passed to result in the production of clonal progeny without a parental contribution. Apomixis is due to modifications of the sexual reproduction and it does not occur in the major crop species, but is found in many wild species like Poa pratensis and Brachiaria brizantha. The idea of this work is to study genes involved in apomixis in apomictic plants, and then studies the function in the model organism Arabidopsis thaliana. In Poa pratensis by the cDNA-AFLP technique several genes differentially expressed in apomictic and sexual genotypes have been isolated. During my PhD I characterized the Arabidopsis homologue of PpAPO1 (Poa pratensis APOSTART 1) that has been renamed AtAPO1. Brachiaria brizantha is an important forage grass. The occurrence of both apomictic and sexual reproduction within Brachiaria makes it an interesting system for understanding the molecular pathways involved in both modes of reproduction.