Structural characteristics of two wheat histone H2A genes encoding distinct types of variants and functional differences in their promoter activity

To investigate the regulation of plant histone H2A gene expression, we isolated two H2A genes (TH254 and TH274) from wheat, which encode two variants of H2A. Both genes had an intron in the coding region. In the promoters, some characteristic sequences, such as Oct and Nona motifs, which are conserved among plant histone genes, were located in a short region (about 120 bp) upstream from the putative TATA box. Transient expression analyses of promoter activity with H2A–GUS fusion genes using tobacco protoplasts revealed novel types of positive cis/-acting sequences in the TH254 promoter: a direct repeat of a 13 bp sequence (AGTTACATTATTG) and a stretch composed of an AT-rich sequence (ATATAGAAAATTAAAA) and a G-box (CACGTG). Quantitative S1 assay of the mRNA amounts from the TH254/GUS and TH274/GUS chimeric genes in stably transformed and cell cycle-synchronized tobacco cell lines showed that the promoters of both genes contained at least one cis/-acting element responsible for S phase-specific expression. Histochemical analysis of transgenic tobacco plants carrying the chimeric genes showed that the promoters of the two H2A genes were active in developing seedlings and flower organs but were regulated in a different manner.