RBR or RBR1 is a retinoblastoma homologue RETINOBLASTOMA-RELATED protein. RBR controls nuclear proliferation in the female gametophyte. It is Also required for correct differentiation of male gametophytic cell types. It regulates stem cell maintenance in Arabidopsis roots. It is involved in the determination of cell cycle arrest in G1 phase after sucrose starvation. RBR1 is also involved in regulation of imprinted genes.
