Objective  This paper aims to investigate the key role of heat shock transcription factor HSF of Populus simonii × P. nigra in response to high temperature and high salt stress.

  Method  Bioinformatics analysis of poplar HSF transcription factor family genes was carried out through multi-sequence alignment, phylogenetic tree construction, analysis of protein physicochemical properties, conserved domains and cis-acting element prediction. In this study, P. simonii × P. nigra was used as a material, and its morphological changes were observed after 37 ℃ high temperature treatment for half a month and the PsnHSFs genes were analyzed for spatio-temporal expression after 37 ℃ high temperature treatment for 0, 12, 24 and 48 h. In addition, P. simonii × P. nigra seedlings were used for 150 mM NaCl stress treatment for 0 and 24 h, the relative expression level of PsnHSFs was analyzed by RNA-seq and verified by RT-qPCR.

  Result  The 29 HSF genes were divided into three subfamilies of A, B and C by structural characteristics and phylogenetic comparison, each subfamily contained 18, 10 and 1 genes. The sequence length of amino acid HSF encoding was between 209 and 595. The HSF proteins were hydrophilic proteins; the N-terminal had a highly conserved DBD domain composed of three conserved motifs. The promoter sequences of the HSF genes contained a variety of cis-acting elements such as DRE core, ABRE and TC-rich elements. After high temperature treatment, the plant height was only 76.51% of control. The leaf was curled and rough, the leaf area was significantly reduced, and the trees had multiple branches which were soft and inflexible. RT-qPCR and RNA-seq results showed that PsnHSFs were induced by high temperature and high salt stress.

  Conclusion  The growth and development of poplar was significantly affected by high temperature, the PsnHSFs genes of poplar play an important role in response to high temperature and high salt stress. This study provides a reference for understanding the HSF family genes in poplar and revealing the molecular mechanism of HSF involved in stress response in woody plants.