The molecular basis of parental conflict driven regulation of endosperm cellularization

The endosperm is a seed tissue supporting embryo growth, similar to the placenta in mammals. It originates after fertilization of the maternal central cell by one of the paternal sperm cells. In the early stages of Arabidopsis thaliana seed development, nuclei divisions in the endosperm are not followed by cellularization. After a defined number of mitotic cycles, the endosperm cellularizes and stops dividing. The timing of endosperm cellularization impacts on final seed size and is differentially controlled by maternal and paternal genome contributions. While increased maternal genome dosage causes early endosperm cellularization and the formation of small seeds, the opposite is caused by increased paternal genome dosage. The parental factors controlling the differential timing of endosperm cellularization remain largely unexplored. Here, we show that a family of maternally expressed auxin response factors ( ARFs ) promotes endosperm cellularization and regulates final seed size. One-Sentence Summary Endosperm cellularization is under antagonistic parental control that converges on Auxin Response Factors.