Cooperation of two distinct cis‐acting elements is necessary for the S phase‐specific activation of the wheat histone H3 promoter

Abstract

We have previously shown that the proximal promoter region (−185 to +57) of the wheat histone H3 gene (TH012) is sufficient for regulating S phase‐specific expression of a reporter GUS gene. To define the cis‐acting element(s) responsible for S phase‐specific expression, GUS fusion genes under the control of wild‐type or variously mutated H3 promoters were stably introduced into cultured rice Oc cells and their temporal expression was analyzed during the cell cycle by quantitative S1 analysis. The S phase‐specific expression of the full‐sized promoter (−1716 to +52) was significantly impaired by short internal deletions disrupting the type I element from −175 to −158 (CCACGTCACCaATCCGCG), composed of the Hex (CCACG‐TCA) and reverse‐oriented Oct (GATCCGCG) motifs. Moreover, the H3 proximal promoters (−184 to +52) harboring base‐substitution mutations in either or both of the Hex and Oct motifs could no longer activate gene expression during the S phase. These results indicate that the type I element is the first cis‐acting element identified responsible for the S phase‐specific expression of plant histone genes. Results also suggested the presence of a redundant cis‐acting element(s) responsible for S phase‐specific expression in the H3 far‐upstream region (−1716 to −185).