Regulates the production of endosperm cells, affecting seed filling and embryo development. Regulates endoreduplication of endosperm cells. May play a role in the exit from the mitotic cell cycle during rice grain formation. Inhibitis leaf elongation rates by decreasing cell number, that is partly compensated by increased cell size. May not affect growth rate or cell size of the primary root. Expressed in roots, stems, leaves and apex. Expressed throughout seed development in the pericarp and endosperm tissues with a peak at 8 days after pollination in the outermost cell layers located centripetally to the endosperm. Down-regulated by cytokinin. Plants overexpressing KRP1 show a reduction in the filling rate of about 2/3, and no embryo is observed in the empty seeds or seeds containing underdeveloped endosperm. Belongs to the CDI family. ICK/KRP subfamily.