A maize histone deacetylase and retinoblastoma-related protein physically interact and cooperate in repressing gene transcription

In mammalian cells the product of the human retinoblastoma tumour suppressor gene (pRb) can recruit Rpd3-like histone deacetylases to repress transcription. In this study, we investigated whether this mechanism might also be relevant in plants and found both conserved and distinct features. The expression profiles of the Zea mays Rpd3- type histone deacetylase (ZmRpd3I) and the retinoblastoma-related (ZmRBR1) homologues were analysed during endosperm development. GST pull-down and immunoprecipitation experiments showed a physical interaction between ZmRBR1 and ZmRpd3I. Because ZmRpd3I lacks a LXCXE motif, conserved in several pRb-interacting proteins, we have mapped the amino acid domains involved in the ZmRBR1/ZmRpd3I interaction. Furthermore, we observed that ZmRbAp1, a maize member of the MSI/RbAp family, facilitated this protein interaction. Cotransformations of tobacco protoplasts with plasmids expressing ZmRBR1 and ZmRpd3I showed that the two proteins cooperate in repressing gene transcription. Our findings represent the first indication that in plants a regulator of important biological processes, ZmRBR1, can recruit a histone deacetylase, ZmRpd3I, to control gene transcription.