Conserved functions of retinoblastoma proteins: From purple retina to green plant cells

The mammalian retinoblastoma susceptibility gene product, known as the first tumor suppressor protein (pRB), has a central role in the regulation of the cell cycle, differentiation and apoptotic pathways of specific cell types. Discoveries in the past decade have shown that key elements of the RB regulatory network also exist in higher plants which control a wide range of cellular functions, including cell division cycle and differentiation. As we outline in this review, the plant RB-related proteins (RBRs) display amino acid sequence similarity and biochemical binding properties analogous to their mammalian homologues and they can interact with E2F transcriptional factors, D-type cyclins and viral proteins. The complex regulatory functions of the retinoblastoma proteins are discussed in detail by focusing in particular on the increasing amount of information being produced about the role of these proteins in higher plants.