Abstract
Seed development in flowering plants is initiated after a double fertilization event with two sperm cells fertilizing two female gametes, the egg cell and the central cell, leading to the formation of embryo and endosperm, respectively. In most species the endosperm is a polyploid tissue inheriting two maternal genomes and one paternal genome. As a consequence of this particular genomic configuration the endosperm is a dosage sensitive tissue, and changes in the ratio of maternal to paternal contributions strongly impact on endosperm development. The FERTILIZATION INDEPENDENT SEED (FIS) Polycomb Repressive Complex 2 (PRC2) is essential for endosperm development; however, the underlying forces that led to the evolution of the FIS-PRC2 remained unknown. Here, we show that the functional requirement of the FIS-PRC2 can be bypassed by increasing the ratio of maternal to paternal genomes in the endosperm, suggesting that the main functional requirement of the FIS-PRC2 is to balance parental genome contributions and to reduce genetic conflict. We furthermore reveal that the AGAMOUS LIKE (AGL) gene AGL62 acts as a dosage-sensitive seed size regulator and that reduced expression of AGL62 might be responsible for reduced size of seeds with increased maternal genome dosage.
Highlights
Seed development in flowering plants is initiated by double fertilization of the female gametophyte
Similar to triploid seeds derived from 4n62n interploidy crosses [6], triploid seeds derived from osd162n crosses had a reduced endosperm proliferation rate (Figure 1C) and an early onset of endosperm cellularization (Figure 1D), correlating with decreased seed size compared to the self-fertilized maternal parents
(2) Bypass of FERTILIZATION INDEPENDENT SEED (FIS)-Polycomb Repressive Complex 2 (PRC2) function is connected with decreased expression of AGL62 and interacting AGAMOUS LIKE (AGL). (3) Decreased seed size of maternal excess triploid seeds is neither mediated by increased activity of FIS-PRC2 and nor by increased levels of p4-small interfering RNAs (siRNAs). (4) Decreased size of maternal excess triploid seeds is likely a consequence of decreased expression of paternally expressed genes
Summary
Seed development in flowering plants is initiated by double fertilization of the female gametophyte. The endosperm of Arabidopsis thaliana follows the nuclear-type of development where an initial syncytial phase of free nuclear divisions without cytokinesis is followed by cellularization [3]. At the eighth mitotic cycle cellularization of the syncytial endosperm is initiated in the micropylar domain around the embryo, coinciding with the early heart stage of embryo development [4,5]. Timing of endosperm cellularization can be manipulated by interploidy hybridizations, which have opposite effects on endosperm cellularization and seed size dependent on the direction of the increased parental genome contribution. Increased maternal genome contribution (4n62n, corresponds to maternal excess hybridization) causes precocious endosperm cellularization and the formation of small seeds
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
