Functional analysis of a RPD3 histone deacetylase homologue in Arabidopsisthaliana

Histone acetylation is modulated through the action of histone acetyltransf erase and deacetylase, which play key roles in the regulation of eukaryotic gene expression. We have screened the expressed sequence tag database with the yeast histone deacetylase RPD3 sequence and identified two Arabidopsis homologues, AtRPD3A and AtRPD3B. The deduced amino acid sequences of AtRPD 3A and AtRPD3B show high overall homology (55% identity) to each other. AtR PD3A encodes a putative protein of 502 amino acids with 49% identity to the yeast RPD3. AtRPD3B encodes a putative protein of 471 amino acids and shar es 55% amino acid identity with the yeast RPD3. Northern analysis indicated that AtRPD3A was highly expressed in the leaves, stems, flowers and young siliques of Arabidopsis plants, whereas the AtRPD3B transcript was not dete cted in these organs. An AtRPD3A fusion protein repressed transcription whe n directed to a promoter driving a reporter gene, indicating a role for AtR PD3A protein in gene repression. Arabidopsis plants were transformed with a gene construct comprising a truncated AtRPD3A cDNA in the antisense orient ation driven by a strong constitutive promoter, -394tCUP. Antisense express ion of AtRPD3A resulted in decreased endogenous AtRPD3A transcript and dela yed flowering in transgenic Arabidopsis plants, suggesting that the transit ion from the vegetative to reproductive phase of development could be affec ted by histone acetylation. Our study demonstrates the important role of hi stone deacetylases in plant growth and development.