The Open Reading Frame(ORF) sequence of a histone deacetylase gene,named HDA901,was cloned from Populus trichocarpa and its sequence,sub-cellular localization and expression under salt stress were analyzed.The ORF of HDA901 is 1 245 bp,encoding a protein consisting of 414 amino acids.The isoelectric point of HDA901 protein is 5.77.Sequence alignment and phylogenetic analysis showed that HDA901 shared a conserved domain with the HDACs in other plants and was relatively close to Arabidopsis AtHDA14 in evolution.Promoter sequence analysis showed that the promoter of HDA901 gene contained multiple stress-related cis-acting elements including ACE,ABRE,HSE and TC-rich repeats.Sub-cellular localization analysis showed that HDA901 was localized neither in nucleus nor in cytoplasm,but might be localized in mitochondria and(or) shuttle between mitochondria and chloroplasts.Real-time PCR analysis showed that the expression of HDA901 gene was in response to salt stress.Under the salt stress,the expression of HDA901 was down-regulated in stem and root,while was up-regulated in leaf.These findings indicated that HDA901 was involved in salt stress response.