Transcriptional regulation in eukaryotes is not simply determined by the DNA sequence, but rather mediated through dynamic chromatin modifications and remodeling. Recent studies have shown that reversible and rapid changes in histone acetylation play an essential role in chromatin modification, induce genome-wide and specific changes in gene expression, and affect a variety of biological processes in response to internal and external signals, such as cell differentiation, growth, development, light, temperature, and abiotic and biotic stresses. Moreover, histone acetylation and deacetylation are associated with RNA interference and other chromatin modifications including DNA and histone methylation. The reversible changes in histone acetylation also contribute to cell cycle regulation and epigenetic silencing of rDNA and redundant genes in response to interspecific hybridization and polyploidy.