GAMETOPHYTE AND SPOROPHYTE CROSSTALK DURING FERTILIZATION IN ARABIDOPSIS

Arabidopsis thaliana seeds comprise three tissues, which are genetically and functionally distinct. However, in order to ensure a correct seed development, a communication and coordination of them is strictly necessary. The seed coat is a five-layer tissue surrounding the female gametophyte. In the stk abs double mutant only four layers form this tissue: the endothelium, the innermost one, does not differentiate. Since the endothelium is a sporophytic layer directly in contact with the gametophyte before the fertilization and with the endosperm after the fertilization, we hypothesized a possible role of this layer in the communication between those tissues. In this work, the role of the endothelium has been investigated, as well as the role of the STK and ABS, the two MADS box transcription factors required for endothelium differentiation. An additional interesting phenotype of the stk abs double mutant is the excessive amount of starch accumulating in the central cell of the female gametophyte. This might causes the partial sterility described for the double mutant. Combining stk abs with the gpt1 mutant, whose mature ovules do not accumulate starch, we found a partial recovery of the phenotype; this result support the idea that the excess of starch in the double mutant could physically prevent the correct fertilization process.