Homeobox Gene (OSH1) Expression in Embryonic Mutants of Rice (Oryza sativa L.)

Recent identification and characterization of plant homeobox genes suggest that they play important roles in morphogenetic events. OSH1, one of the rice homeobox genes, is thought to be related to organ development since the changes of OSH1 gene expression cause morphological abnormalities of leaves by the ectopic expression and is expressed during early embryogenesis. In this experiment, the expression pattern of OSH1 was analyzedinmutants by in situ hybridization, and OSH1's potential as a molecular marker was explored. Region-specific expression of OSH1 during early embryogenesis shows that OSH1 could be used as a molecular marker for characterizing embryo mutants. Although several organless and shootless mutants showed normal expression of OSM1, some mutants exhibited abnormal expression patterns. In a minute organless cle1-1 embryo whose epidermis resembled morphologically the epithelium of scutellum, OSH1 expression was limited to a small basal region. This expression pattern suggests the gross deletion of the basal part. In a radicleless mutant, odm115, OSH1 expression was detected in a basal region instead of subcentral region of the ventral side. Together with other characteristics (short embryo and normal adventitious roots), odm115 was estimated to be derived from the deletion of basal region. Among five shootless mutants, three showed normal expression of OSH1. In the shl2 embryo, no expression of OSH1 was observed. In the shl1 embryo, however, OSH1 expression was extended to a dorsal side, indicating that SHL2 might be related to dorsoventral patterning. The above results of in situ hybrydization clearly indicate that OSH1 can be utilized as a marker for characterizing gene functions of embryo mutants.