Arabidopsis E2F1 binds a sequence present in the promoter of S-phase-regulated gene AtCDC6 and is a member of a multigene family with differential activities

Mammalian E2F transcription factors are composed of E2F and DP subunits, and with their negative regulators, Rb-related proteins, govern expression of cell-division-related genes. Six E2Fs and two DPs are present in mammals, but only single E2F genes are known from wheat, tobacco and carrot. Here we show that E2Fs are a multigene family in Arabidopsis, and report isolation of three E2F-like clones AtE2F1-3, with 45-62% identity to wheat, tobacco and carrot E2Fs. Sequence analysis reveals that AtE2F1 and AtE2F3 are closely related to previously identified plant E2Fs, whereas AtE2F2 is related to human E2F6 and Drosophila dE2F2 which are unusual in lacking transcriptional activation potential. Consistent with this, we show that AtE2F1 and AtE2F3 activate transcription in yeast cells and bind a plant Rb protein, but AtE2F2 cannot activate transcription or bind Rb. Consensus E2F-binding sites were identified in promoters of several cell cycle related genes, including the D-type cyclin CycD3 and the Arabidopsis homologue of the replication origin protein CDC6. Accumulation of AtE2F1-3 was observed in partially synchronised Arabidopsis cells re-entering the cell cycle, before induction of CycD3 and CDC6 expression in late G1. AtE2F1 complexes bound to consensus E2F sequences and to the AtCDC6 promoter in vitro. We conclude that Arabidopsis contains a family of functionally distinct E2F genes, most probably involved in the G1-to-S phase progression.