Hierarchical regulation of organ differentiation during embryogenesis in rice

In plants, genetic mechanisms leading to shoot and root formation are almost unknown. Because basic body organization of such organisms is established during embryogenesis, induction and isolation of embryonic mutants is a promising approach to the study of plant development. The study of available embryonic mutants of rice indicates the existence of three major developmental processes taking place during embryogenesis before morphogenetic events start: determination of organ differentiation, positional regulation of organs and size regulation of the embryo. The consideration of specific rice mutants supports the existence of two types of mutations in each regulatory process, one affecting the embryo as a whole and the second concerning more restricted embryonal regions. A hierarchical type of control of rice embryogenesis is suggested.