Genetic Dissection of Parent of Origin Effects in Seed Development
Friday Seminar by Paul Grini.
In the developing progeny of mammals the two parental genomes are differentially expressed directed by imprinting marks and embryos with only a uniparental genetic contribution die. A parent of origin dependent expression has also been observed in the offspring of flowering plants and mutations in the imprinting machinery lead to embryonic lethality primarily affecting the development of the endosperm, a structure in the seed that nourishes the embryo analogous to the mammalian placenta. Seed development is the product of the double fertilization of the egg cell and the central cell by two sperm cells from the pollen and requires a coordinated interplay of the embryo, the endosperm and the maternal seed coat. We have used a mutant in the Arabidopsis Cdc2/CDC28 homologue, CDKA;1 as a tool to dissect the involvement of parental gene programs in seed development. cdka;1 mutant pollen fails to undergo the second pollen mitosis, resulting in pollen with a single sperm cell that exclusively fertilize the egg cell. Although not fertilized, the central cell in cdka;1 ovules with fertilized egg cells is triggered to initiate endosperm proliferation(1). Surprisingly, viable seedlings can develop from seeds lacking a paternal contribution to the endosperm, given the mother is mutant for any of the FIS genes that encode Polycomb group (PcG) chromatin remodelling factors.
Thus, these data provide functional evidence that the action of the FIS complex balances the contribution of the paternal genome(2). As flowering plants have evolved a special reproduction system with a parallel fusion of two female with two male gametes, our findings support the hypothesis that only with the evolution of double fertilization did the action of the FIS genes become a requirement for seed development. Furthermore, our data argue for a gametophytic origin of endosperm in flowering plants, thereby supporting a hypothesis raised in 1900 by Eduard Strasburger(3). In order to identify further factors involved in cross talk between the components of the seed and parent of origin specific regulation of seed development, we have generated microarray transcriptional profiles of seeds with uniparental endosperm. Our preliminary data identifies several regulated genes that could represent novel paternal specific transcripts (downregulated) or maternal targets of paternal repressors (upregulated).
The CEES seminar room has a coffee-machine – it is therefore recommended that you come a bit earlier and get yourself a good cup of coffee (for the price of 3 NOK).