Roles of rice GL2-type homeobox genes in epidermis differentiation

GL2-type genes have been recognized as plant-specific homeobox genes involved in epidermis development. Here we report the isolation and characterization of rice GL2-type homeobox genes. The BLAST searches using the rice genomic database revealed that there are at least nine GL2-type homeobox genes (Roc1-Roc9) in the rice genome. Among them, we have isolated full cDNA clones of five Roc genes, including previously reported Roe]. GL2-type homeodomain proteins have a dimerization motif, consisting of two leucine zipper-like motifs (LZ1 and LZ2) interrupted by a loop, adjacent to the C-terminal part of the homeodomain. The Roc proteins can form both homo- and hetero-dimers through leucine zipper motifs in various combinations. In situ hybridization, RNA gel blot analysis and RT-PCR experiment revealed that the five Roe genes commonly showed an epidermis-specific expression, but partially differed in the temporal expression pattern. These results suggest that the Roc genes can regulate a variety of processes in epidermis differentiation in a combinatorial way.