Histone acetylation is one of the vital reversible modifications of chromatin structure that regulates gene expression in eukaryotes. Histone acetyltransferases (HATs) and histone deacetylases (HDACs) maintain the homeostasis of histone acetylation. Studies in Arabidopsis have revealed that HATs are involved in plant responses to various stresses including light, temperature, salt and ABA. Drought stress, a very common environmental stress, could cause a range of physiological and biochemical responses in plants involving HATs. Eight HATs in four different families (CBP, GNAT, MYST, and TAF(II)250 family) are known in rice. In this research, four OsHATs, one from each family, were chosen based on in silica domain and promoter analysis for their response under drought conditions. Drought stress was introduced to two-leaf-stage rice seedlings. The effectiveness of drought treatment was confirmed by the measurement of relative water content (RWC). Real-time quantitative polymerase chain reaction analysis demonstrated that drought stress caused a significant increase in the expression of four HATs (OsHAC703, OsHAG703, OsHAF701 and OsHAM701) in rice plants. Additionally, the Western-blot analysis showed that the acetylation level on certain lysine sites of H3 (lysine 9, lysine 18 and lysine 27) and H4 (lysine 5) increased with OsHATs expression. The significant increase in the transcript levels of OsHATs and the acetylation level of lysine residues on Histone H3 and H4 suggest that OsHATs are involved in drought stress responses in rice. (C) 2013 The Authors. Published by Elsevier Inc. All rights reserved.