Abstract: In order to investigate the function of HMG（High mobility group proteins） genes under abiotic stresses in Populus davidiana×P.bolleana,the HMG genes were cloned and the stress tolerant function of HMGs was identified,and the theoretical foundation for using the gene in tree breeding through genetic engineering was laid.Seven homologous genes of Arabidopsis HMGs（named PdbHMG1-7） were found by homologous sequence alignment,and sequence analysis of PdbHMG1-7 was performed using bioinformatics tools respectively,the expression patterns of PdbHMG1-7 gene in leaves and roots of Populus davidiana×P.bolleana under different stresses were investigated by qRT-PCR.Results The ORF length of PdbHMG1-7 were 456-2 004bp respectively,the amino acid residues encoded by PdbHMG1-7 genes were 151-667 aa,and the molecular weight of the encoded protein were 16.72-75.54 kDa,and the theoretical isoelectric point were 5.35-9.36,and the seven PdbHMG were hydrophilic proteins.The results of multiple sequence alignment and phylogenetic tree analysis showed that all 7 PdbHMG genes contained HMG-box conserved domains and belonged to HMGB subfamily.The analysis results of cis-acting elements contained in the promoter showed that the promoter sequence of PdbHMG genes contained a variety of elements in response to hormones and stress.The expression pattern analysis showed that the expression levels of seven PdbHMGs in roots and leaves under NaCl,PEG₆₀₀₀,ABA and CdCl₂ stress treatment changed in at least one stress treatment time point respectively.In leaves,PdbHMG2 were induced under the stress of NaCl,PEG6000,ABA and CdCl₂,and almost all of them were significantly up-regulated respectively,but PdbHMG7 was down-regulated.Under NaCl and CdCl₂ stress,PdbHMG1,PdbHMG3 and PdbHMG6 were almost significantly up-regulated during the whole stress process respectively.The expressions of PdbHMG3 in leaves were also significantly up-regulated at most time points under NaCl and CdCl₂ stress.In roots,the expression of PdbHMG3 and PdbHMG5 was significantly upregulated in the whole process of NaCl treatment.However,PdbHMG6 was not significantly expressed during NaCl stress except for 9-12 h,the expression of PdbHMG6 was significantly down-regulated at other stress time points.During ABA treatment,PdbHMG6 was down-regulated in roots.Conclusion The results showed that seven PdbHMG genes could respond to at least one stress treatment in one organ,but the types and mechanisms of involved stress response might be different.This study provided a reference for further studying the function of PdbHMGs family genes in Populus davidiana×P.bolleana.