Post-translational modification of histones, in particular acetylation, is
an important mechanism in the regulation of eukaryotic gene expression. His
tone deacetylases are enzymes that remove acetyl groups from the core histo
nes and play a key role in the repression of transcription. HD2 is a maize
histone deacetylase, which shows no sequence homology to the histone deacet
ylases identified from other eukaryotes. We have identified two putative HD
P-like histone deacetylase cDNA clones, AtHD2A and AtHD2B, from Arabidopsis
thaliana by screening the expressed sequence tag database. AtHD2A and AtHD
2B encode putative proteins of 246 and 305 amino acids, and share 44% and 4
6% amino acid identity to the maize HD2, respectively. Northern blot analys
is indicated that AtHD2A was highly expressed in flowers and young siliques
of Arabidopsis plants, whereas AtHD2B was widely expressed in stems, leave
s, flowers and young siliques. AtHD2A repressed transcription when directed
to a promoter containing GAL4 binding sites as a GAL4 fusion protein. Dele
tion of the extended acidic domain or the domain containing predicted catal
ytic residues of AtHD2A resulted in the loss of gene repression activity, r
evealing the importance of both domains to AtHD2A function. Arabidopsis pla
nts were transformed with a gene construct comprising an AtHD2A cDNA in the
antisense orientation driven by a strong constitutive promoter, -394tCUP.
Silencing of AtHD2A expression resulted in aborted seed development in tran
sgenic Arabidopsis plants, suggesting that the AtHD2A gene product was impo
rtant in the reproductive development of Arabidopsis thaliana.