Isolation and characterization of a rice homeobox gene, OSH15

In many eukaryotic organisms including plants, homeobox genes are thought t o be master regulators that establish the cellular or regional identities a nd specify the fundamental body plan. We isolated and characterized a cDNA designated OSH15 (Oryza sativa homeobox 15) that encodes a KNOTTED-type hom eodomain protein. Transgenic tobacco plants overexpressing the OSH15 cDNA s howed a dramatically altered morphological phenotype caused by disturbance of specific aspects of tobacco development, thereby indicating the involvem ent of OSH15 in plant development. We analyzed the in situ mRNA localizatio n of OSH15 through the whole plant life cycle, comparing the expression pat tern with that of another rice homeobox gene, OSH1. In early embryogenesis, both genes were expressed as the same pattern at a region where the shoot apical meristem would develop later. In late embryogenesis, the expression pattern of the two genes became different. Whereas the expression of OSH1 c ontinued within the shoot apical meristem, OSH15 expression within the shoo t apical meristem ceased but became observable in a ring shaped pattern at the boundaries of some embryonic organs. This pattern of expression was sim ilar to that observed around vegetative or reproductive shoots, or the flor al meristem in mature plants. RNA in situ localization data suggest that OS H15 may play roles in the shoot organization during early embryogenesis and thereafter, OSH15 may be involved in morphogenetic events around the shoot apical meristem.