Abstract
In flowering plants, seed development is initiated by the fusion of the maternal egg and central cells with two paternal sperm cells, leading to the formation of embryo and endosperm, respectively. The fertilization products are surrounded by the maternally derived seed coat, whose development prior to fertilization is blocked by epigenetic regulators belonging to the Polycomb Group (PcG) protein family. Here we show that fertilization of the central cell results in the production of auxin and most likely its export to the maternal tissues, which drives seed coat development by removing PcG function. We furthermore show that mutants for the MADS-box transcription factor AGL62 have an impaired transport of auxin from the endosperm to the integuments, which results in seed abortion. We propose that AGL62 regulates auxin transport from the endosperm to the integuments, leading to the removal of the PcG block on seed coat development.
Highlights
In flowering plants, fertilization of the two female gametes, egg cell and central cell by the two male sperm cells results in the development of the embryo and the endosperm, a nourishing tissue which supports embryo growth
We demonstrate that application of auxin is sufficient to drive seed coat development and that AGL62 regulates the expression of P-GLYCOPROTEIN 10 (PGP10), in the endosperm, which likely functions as an auxin transporter to the sporophytic tissues
Auxin and gibberellin signaling are active in the developing seed coat Seed coat initiation is dependent on the fertilization of the central cell by one of the paternally-contributed sperm cells, but this requirement can be bypassed in mutants of sporophytic Polycomb Repressive Complex 2 (PRC2) components that initiate the autonomous development of the seed coat (Roszak and Kohler, 2011)
Summary
Fertilization of the two female gametes, egg cell and central cell by the two male sperm cells results in the development of the embryo and the endosperm, a nourishing tissue which supports embryo growth. These two fertilization products are surrounded by the seed coat, a sporophytic tissue of purely maternal origin. Mutations that affect seed coat expansion limit endosperm growth, such as transparent testa glabra 2 (Garcia et al, 2005), while mutants with increased integument cell proliferation like megaintegumenta/auxin responsive factor 2, result in enlarged seeds with more abundant endosperm (Schruff et al, 2006). The absence of the endothelium integument layer results in seed abortion, highlighting the importance of the developing seed coat for the establishment of a viable seed (Mizzotti et al, 2012)
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