MATERNAL CONTROL OF SEED DEVELOPMENT: THE ROLE OF THE MADS-BOX GENES SEEDSTICK AND ARABIDOPSIS B SISTER.

The haploid generation of flowering plants develops within the sporophytic tissues of the ovule that protect the female gametophyte developing inside. After fertilization the maternal seed coat develops in a coordinated manner with the embryo and endosperm and undergoes several changes including accumulation of secondary metabolites such as proanthocyanidins and mucilage. The research performed in these three years had the goal to investigate the interaction between the two generations. In particular we have identified key factors, expressed in the seed integuments (maternal tissue) controlling several aspects of seed development. In the arabidopsis bsister (abs) mutant the endothelium, does not accumulate proanthocyanidins and cells have an abnormal morphology (ref). ABS encode for a transcription factor belonging to MADS box family. Another MADS-box gene, SEEDSTICK regulates redundantly with SHATTERPROOF 1 (SHP1) and SHP2 ovule identity (ref). Here we describe the characterization of the abs stk double mutant. This double mutant develops very few seeds due to both a reduced number of fertilized ovules and seed abortions later during development. Morphological analysis revealed the total absence of the endothelium in this double mutant. Additionally, massive starch accumulation was observed in the embryo sac. The abs stk analysis strongly suggests a maternal role in the regulation of the fertilization process and highlights the importance of the endothelium for the development of the next generation. Here we also report new functions of the MADS-box transcription factor STK during seed development. stk mutant seeds present defect in seed coat morphology and abnormal proanthocyanidins accumulation. In addition, stk mutant seeds present problems in mucilage release. Our data reveal new functions of STK after fertilization highlighting the importance of this transcription factor indicated as a key regulator of seed development.