Apical displacement1 gene regulates apical-basal pattern formation in rice embryo

We analyzed an embryo mutant apical displacement1 (apd1) that formed an underdeveloped shoot at the apex of the embryo and one or two radicles in the enlarged basal region. At the early embryonic stage, apd1 initiated shoot and radicle in almost normal positions. However, in later stages, reduction of the apical region and enlargement of the basal region became gradually more pronounced. Consequently, a shoot and a radicle were shifted toward the apical position; the second radicle was formed below the first one. The apd1 plant showed pleiotropic phenotypes in shoots and roots: many tillers, narrow leaves, short roots and small inflorescences. In shl1-2apd1 double mutant, a shoot was deleted, as in shl1-2. In addition, the number of radicles was more than that of apd1. This result suggests that APD1 and SHL1 function redundantly in the regulation of basal region size. Taken together, these results suggest that APD1 gene regulates the development of shoot and the regionalization along apical-basal axis. Moreover, we infer that in rice embryogenesis, sizes of apical and basal regions are under compensatory regulation.