Proceedings of the XLVI Italian Society of Agricultural Genetics - SIGA Annual Congress

Giardini Naxos, Italy - 18/21 September, 2002

ISBN 88-900622-3-1

Oral Communication Abstract - S5g

FUNCTIONAL CHARACTERIZATION OF RPD3-LIKE HISTONE DEACETYLASES IN MAIZE

LOCATELLI S., MOTTO M., ROSSI V.

Istituto Sperimentale per la Cerealicoltura - Bergamo

Zea mays, histone deacetylases, epigenetic factors

Gene expression can be stably modified by epigenetic components that can either silence or superactive selected DNA templates. Among these components are factors affecting chromatin structure by covalent modification of histones. It has been shown that histone modifications define epigenetic marks within the genome, thus establishing an “epigenetic code” superimposed to the DNA-code based control of gene activity.

Histone acetyltransferases (HATs) and deacetylases (HDACs) are the best characterized enzymes involved in the control of histone modification; in particular, a positive, although not general, correlation between histone acetylation and gene activity has been proposed. HATs and HDACs have been identified and characterized in plant systems and it has been shown that the basic features of histone acetylation in plants resemble those of other eukaryotes, although plant-specific features has also been reported.

It has been shown that HDACs are involved in several pathways for transcriptional repression This is best illustrated by the product of the retinoblastoma tumor suppressor gene (pRb) that can recruit mammalian Rpd3-type class I HDACs to repress gene transcription. Specifically, the binding of the Rpd3/pRb complex to members of the E2F family of transcriptional activators results in the formation of a transcriptionally incompetent chromatin environment, thus repressing the expression of E2F-target genes and, consequently, prevents cell cycle progression at the G1/S transition. Since several components of the pRb/E2F pathway and the basic features of histone acetylation are conserved in metazoans and plants we investigated whether this mechanism might also be relevant in plants. Our study demonstrate that ZmRpd3I, a maize class I HDAC, can associate with ZmRBR1, a maize retinoblastoma-related protein, and that the two proteins cooperate in repressing gene transcription. This provides the first evidence that plant HDACs can be recruited by a regulator of important biological processes to control gene transcription and found both conserved and distinct features.

The monocot maize (Zea mays ) is a model organism for the detailed biochemical, enzymatic, and molecular characterization of different HAT and HDAC types. Three different maize Rpd3-like genes have been identified so far. To understand the biological role of the maize Rpd3-type HDACs we have analyzed the expression and localization profile of Rpd3 genes. In addition, Mu-tagged mutants and transgenic plants with an altered level of ZmRpd3I HDAC activity have been characterized.