A type I element composed of the hexamer (ACGTCA) and octamer (CGCGGATC) motifs plays a role(s) in meristematic expression of a wheat histone H3 gene in transgenic rice plants.

Type I element (CCACGTCACCGATCCGCG) is a well-conserved regulatory element found in proximal promoter region of a certain class of plant histone genes, that is composed of two independent cis-acting elements of the hexamer (ACGTCA) and the reverse-oriented octamer (GATCCGCG) motifs. To investigate functional role(s) of the type I element in regulation of a wheat histone H3 gene (TH012) promoter activity in vivo, base substitution mutations were introduced into the element and activities of the mutated promoters were examined in cultured rice cells, and in regenerated roots and anther walls of transgenic rice plants by employing a GUS reporter system. Mutations of each or both of the hexamer and the octamer motifs caused a reduction in the promoter activity in protoplasts transfected transiently or stably transformed calli. The mutation of the octamer motif with or without the mutation of the hexamer motif caused a marked reduction of the promoter activity in the root meristem of transgenic rice although the mutation of the hexamer motif alone caused a weak reduction. In contrast to these results, no effect of the mutations of either the hexamer or the octamer motif was found in the anther wall in which replication-independent activity of the H3 promoter was observed. Our results suggested that the hexamer and the octamer motifs may play important role(s) in regulation of replication-dependent but not of replication-independent expression of the wheat histone H3 gene.