Cell cycle regulators and development in plants.

The flowering plant Arabidopsis thaliana contains six E2F genes (AtE2F a-f ) which act as activators or repressors/inhibitors of E2F-responsive genes. Remarkably, a subset of these factors (AtE2Fd-f) is characterized by the absence of a transactivation domain and the presence of two DNA-binding domains which allow them to bind E2F cis-elements without a DP partner. We have investigated the role of AtE2Fd during cell cycle progression and development, as already verified for the other two inhibitory AtE2F proteins (AtE2Fe and f). Promoter analyses revealed that the AtE2Fd gene is highly expressed in mature tissues, whereas the AtE2Fe gene appears to be mainly expressed in proliferating tissues. Immunolocalization analyses showed that the AtE2Fd protein is preferentially accumulating in mature leaves and flowers. However, RT-PCR analysis detected constant levels of AtE2Fd transcripts in both young and mature leaves, suggesting that AtE2Fd accumulation is regulated post-transcriptionally. We are currently asking whether the absence of AtE2Fd protein in proliferating cells reflects translational control and/or protein turn-over