Post-translational modifications of histone proteins play a crucial role in 
responding to environmental stresses. Histone deacetylases (HDACs) catalyze the 
removal of an acetyl group from histones and are generally believed to be a 
transcriptional repressor. In this paper, we report that cold treatment highly 
induces the up-regulation of HDACs, leading to global deacetylation of histones 
H3 and H4. Treatment of maize with the HDAC inhibitor trichostatin A (TSA) under 
cold stress conditions strongly inhibits induction of the maize cold-responsive 
genes ZmDREB1 and ZmCOR413. However, up-regulation of the ZmICE1 gene in 
response to cold stress is less affected. The expression of drought and salt 
induced genes, ZmDBF1 and rab17, is almost unaffected by TSA treatment. Thus, 
these observations show that HDACs may selectively activate transcription. The 
time course of TSA effects on the expression of ZmDREB1 and ZmCOR413 genes 
indicates that HDACs appear to directly activate the ZmDREB1 gene, which in turn 
modulates ZmCOR413 expression. After cold treatment, histone hyperacetylation 
and DNA demethylation occurs in the ICE1 binding region, accompanied by an 
increase in accessibility to micrococcal nuclease (MNase). The two regions 
adjacent to the ICE1 binding site remain hypoacetylated and methylated. However, 
during cold acclimation, TSA treatment increases the acetylation status and 
accessibility of MNase and decreases DNA methylation at these two regions. 
However, TSA treatment does not affect histone hyperacetylation and DNA 
methylation levels at the ICE1 binding regions of the ZmDREB1 gene. Altogether, 
our findings indicate that HDACs positively regulate the expression of the 
cold-induced ZmDREB1 gene through histone modification and chromatin 
conformational changes and that this activation is both gene and site selective.