Regulation of wheat histone gene expression

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Abstract
A chimeric gene composed of the wheat histone H3 promoter and the coding region of bacterial β‐glucuronidase (GUS) gene is expressed in a cell cycle‐dependent manner in transformed cultured rice cells. The same gene also is expressed in meristematic tissues such as root tips and in nondividing tissues such as the anther wall and pistil of transgenic rice plants. All these types of expression are conferred by the region from —185 to +57 in the promoter. Within this region, at least three types of cw‐acting elements are present: hexamer (ACGTCA), octamer (CGCGGATC), and nonamer (CATCCAACG). These motifs are the most probable candidates for the cis‐acting elements that control cell cycle‐dependent and/or tissue‐specific expression of histone genes. The hexamer motif interacts specifically with the wheat nuclear DNA binding proteins HBP‐la and HBP‐lb, and the nonamer motif interacts with HBP‐2. Analysis of the primary structures of the cDNAs encoding HBP‐la and HBP‐lb established that both proteins are bZIP‐type transcription factors. The roles of these cis‐acting elements and trans‐acting factors in the regulation of wheat histone gene expression are discussed.