| dc.description.abstract | Epigenetic regulation is a mechanism by which heritable changes in gene expression are controlled by chromatin status rather than primary DNA sequence. Changes in chromatin structure affect accessibility of DNA elements to the transcriptional machinery and thus affect transcription activity of the gene. A key event in this process is reversible modification of core histones, which is catalyzed by histone acetyltransferases (HATs) and histone deacetylases (HDs, HDAs, or HDACs). In general, histone deacetylation is related to transcriptional gene silencing, whereas acetylation is associated with gene activation.To study the role of histone deacetylase in plant gene regulation and development, we generated constitutive antisense histone deacetylase 1 (CASH) transgenic plants. AtHD1 is a homolog of RPD3 protein, a global transcriptional regulator in yeast. Expression of the antisense AtHD1 caused dramatic reduction in endogenous AtHD1 transcription, resulting in accumulation of acetylated histones. Down-regulation of histone deacetylation caused a variety of growth and developmental abnormalities and ectopic expression of tissue-specific genes. However, changes in genomic DNA methylation were not detected in repetitive DNA sequences in the transgenic plants.We also identified a T-DNA insertion line in exon 2 of AtHD1 gene (athd1-t1), resulting in a null allele at the locus. The complete inhibition of the AtHD1 expression induced growth and developmental defects similar to those of CASH transgenic plants. The phenotypic abnormalities were heritable across the generations in the mutants. When the athd1-t1/athd1-t1 plants were crossed to wild-type plants, the mutant phenotype was corrected in the F1 hybrids, which correlated with the AtHD1 expression and reduction of histone H4 Lys12 acetylation. Microarray analysis was applied to determine genome-wide changes in transcriptional profiles in the athd1-t1 mutant. Approximately 6.7% (1,753) of the genes were differentially expressed in leaves between the wild-type (Ws) and the athd1-t1 mutant, whereas 4.8% (1,263) of the genes were up- or down-regulated in flower buds of the mutant. These affected genes were randomly distributed across five chromosomes of Arabidopsis and represented a wide range of biological functions. Chromatin immunoprecipitation assays indicated that the activation for a subset of genes was directly associated with changes in acetylation profiles. | en |
