Dynamic and Reversible Changes in Histone H3-Lys4 Methylation and H3 Acetylation Occurring at Submergence-inducible Genes in Rice

Histone modifications such as methylation and acetylation in the chromatin surrounding a gene are thought to regulate transcriptional activity. In this study, to determine whether dynamic changes occur in histone modification on the loci of stress-responsive genes in plants, we chose rice submergence-inducible ADH1 and PDC1 genes. When submerged, the rice ADH1 and PDC1 genes were activated in a biphasic manner: the first and second inductions occurred after approximately 2 and 12 h of submergence, respectively. Their expression was transcriptionally induced as shown by increased binding of RNA polymerase II to the ADH1 and PDC1 loci during submergence. The Lys4 residues of the histone H3 proteins (H3-K4s) at both the 5'- and 3'-coding regions of ADH1 and PDC1 were found to change from a di-methylated state to a tri-methylated state at the first induction period. On the other hand, acetylation of H3 increased throughout ADH1 and PDC1 genes at the later induction period. The methylation and acetylation levels recovered to the initial levels during re-aeration. Treatment of seedlings with a histone deacetylase (HDAC) inhibitor, trichostatin A, increased acetylation of histones H3 and association of RNA polymerase II on the ADH1 and PDC1 loci, thereby increasing transcript levels of ADH1 and PDC1. Together, these results showed dynamic and reversible changes of histone H3-K4 methylation and H3 acetylation in stress-responsive genes in a higher plant in response to the appearance or disappearance of an environmental stress.