GENETIC NETWORK CONTROLLING FEMALE GAMETOPHYTE AND EMBRYO DEVELOPMENT IN ARABIDOPSIS THALIANA

The aim of the research performed is the molecular understanding of genes regulating embryo sac development. The identification of genes involved in female gametophyte formation is of significant interest since they are of great importance for plant reproduction. In the last year, different researches have been done in order to identify genes important for embryo sac development. In particular, I was interested in the identification of genes necessary for normal embryo-sac development and genes that can perturb the normal development of the embryo sac. AGL23 was isolated after a large T-DNA insertional mutant screening in type I MADS-box genes. The results presented in chapter 1 indicate that AGL23 is necessary for female gametophyte and embryo development. Indeed, in agl23 mutant the functional megaspore is not able to undergoes mitosis, and in the embryo chloroplast are not able to differentiate, strongly suggesting a role in organelle biogenesis. In several organisms it has been shown that MADS-box proteins form dimers and multimeric complexes. In chapter 2, the interaction between AGL23 and other MADS-box proteins were studied. Indeed, AGL23 interacts with AGL86 in yeast two-hybrid assay. AGL86 is also able to forms hetero-dimers with AGL28, but AGL28 and AGL23 do not interact together. To validate these interaction in vivo, expression analyses using GUS reporter gene and mutant characterisation were done and are described in chapter 2. Furthermore, in order to identify the pathway in which AGL23 is involved, in chapter 3, I focused on the identification of AGL23 target genes. Using a bioinformatic approach, LMW59 was identified as hypothetical target. In this chapter, I described LMW59 functional characterisation. As alternative approach, I also characterized in chapter 4 two lipid-binding START domain-containing genes, AtAPOSTART1, that could be involved in female gametophyte development. AtAPOSTART1 is the homologous gene in Arabidopsis thaliana of APOSTART1 gene of Poa pratensis. In Poa pratensis, Albertini and co-workers (2005) isolated and characterized APOSTART genes like candidate genes involved in apomixis. Apomixis is an asexual way of reproduction and avoids both meiotic reduction and egg fertilization.