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

Giardini Naxos, Italy - 18/21 September, 2002

ISBN 88-900622-3-1

Poster Abstract - 3.33

DIFFERENTIAL EXPRESSION OF RPD3 GENES IN MAIZE

LOCATELLI S.*, ROSSI V.*, VAROTTO S.**

*) Istituto Sperimentale per la Cerealicoltura, Bergamo

**) Dipartimento di Agronomia Ambientale e Produzioni Vegetali, Università di Padova

Zea Mays, histone deacetylases, endosperm, in situ hybridization

Chromatin structure is essential for nuclear processes such as DNA replication, transcription, DNA repair and recombination. It changes in a dynamic way and is continuously remodeled. The basic unit of eukaryotic chromatin is the nucleosome core particle, a repeating element consisting of a histone octamer with 146 bp of DNA wrapped around it. N- terminal tails of histones protrude from the octamer and are subject to post translational modifications. In particular a nucleosome contains a total of 26 potentially acetylated lysine residues. Histone acetyltransferases (HATs) transfer the acetyl moiety of acetyl –CoA to the e -amino group; this reaction is reversed by the action of histone deacetylases (HDACSs; Lusser et al .2001 Trends Plant Sci 2 : 59-66). The monocot maize (Zea maize ) is a model organism for the molecular characterization of different HAT and HDAC types. cDNA sequences of different members of both HDACs of class I (which refer to yeast Rpd3) and class II (which refer to yeast HDA1) have been identified in maize ( Rossi et al. 1998 Mol Gen Gen 258 : 288-296; Lusser et al. 1999 Nucleic Acds Res. 27:4427-4435; Lechner et al. 2000 Biochemistry 39: 1683-1692).

We have identified and cloned cDNA sequences encoding at least three different maize Rpd3-type HDACs. All these proteins posses a HDAC domain, related to HDAC activity and highly conserved in all eukaryotic Rpd3 proteins. Conversely, the N- and C-terminal domains are characteristic for each Rpd3 protein. In order to clarify if these genes have distinct or redundant functions a detailed expression analysis was performed. Rpd3 genes and proteins are expressed in maize endosperm starting at 5 days after pollination (DAP) at the cellularization phase of endosperm development. The expression is abundant up to 12 DAP when endoreduplication occurs in endosperm cells, which - from now on - begin to accumulate starch. Later on during endosperm maturation phase Rpd3 genes expression decline. In situ hybridization experiments show that at 12 DAP all three Rpd3 transcripts localized in all the endosperm cell domains, with the exceptions of aleurone and tranfer cells, which represent highly specialized endosperm tissues. Thus we concluded that the three Rpd3 genes are differentially expressed during endosperm development but co-localized in maize kernels. Immunolocalization experiments carried out on maize sections at 14 DAP with an antibody that identified only one out of the three Rpd3 proteins indicated that this HDAC is expressed both in nucleus and cytoplasm: these observations are in agreement with the idea that HDAC of class I might shuttle between nuclei and cytoplasm in a differentiation dependent manner (Lusser et al . 2001 Trends Plant Sci 2 : 59-66).

To better investigate on the relation between Rpd3 genes expression and cell differentiation in maize, experiments will be performed on shoot apex during vegetative development and on reproductive organs and tissues.