OsKRP1 overexpression in rice plants reduces seed yield by ~70%, caused by a drop in the seed-filling rate and, by a decrease in the average seed weight. Section of seed from overexpression lines showed that the outermost endosperm cell layers occupy a large part of the endosperm space, making a number of cavities, whereas the most inner layers are absent (Barrôco et al., 2006). KRP overproduction impairs the production of a sufficient number of cell layers. mRNA hybridization results showed that OsKRP1 is mostly expressed 8 h after pollination in the cell layers along the periphery of the developing endosperm (Barrôco et al., 2006).