A NOVEL CIS-ACTING ELEMENT IN PROMOTERS OF PLANT B-TYPE CYCLIN GENES ACTIVATES M-PHASE-SPECIFIC TRANSCRIPTION

Plant B-type cyclin genes are expressed late in the G(2) and M phases of the cell cycle. Previously, we showed that the promoter of a Cathar anthus roseus B-type cyclin, GYM, could direct M phase-specific transc ription of a P-glucuronidase reporter gene in synchronously dividing B Y2 tobacco cells. In this study, we determined the regulatory elements contained within the CYM promoter by using a luciferase reporter gene . Mutational analysis showed that a 9-bp element is essential for M ph ase-specific promoter activity in synchronized BY2 cells. The CYM prom oter contains three other sequences similar to this element. A gain-of -function assay demonstrated that when fused to a heterologous promote r, these elements are sufficient for M phase-specific expression; ther efore, we named these elements M-specific activators (MSAs). We found MSA-like sequences in B-type cyclin promoters from tobacco, soybean, a nd Arabidopsis as well as in the promoters of two M phase-specific gen es, NACK1 and NACK2, which encode tobacco kinesin-like proteins. Thus, MSA may be a common cis-acting promoter element that controls M phase -specific expression of cell cycle-related genes in plants.