Molecular evolution and expression divergence of the Populus euphratica Hsf genes provide insight into the stress acclimation of desert poplar

Heat shock transcription factor (Hsf) family is one of the most important regulators in the plant kingdom. Hsf has been demonstrated to be involved in various processes associated with plant growth, development as well as in response to hormone and abiotic stresses. In this study, we carried out a comprehensive analysis of Hsf family in desert poplar, Populus euphratica. Total of 32 genes encoding Hsf were identified and they were classified into three main classes (A, B and C). Gene structure and conserved motif analyses indicated that the members in each class were relatively conserved. Total of 10 paralogous pairs were identified in PeuHsf family, in which nine pairs were generated by whole genome duplication events. Ka/Ks analysis showed that PeuHsfs underwent purifying selection pressure. In addition, various cis-acting elements involved in hormone and stress responses located in the promoter regions of PeuHsfs. Gene expression analysis indicated that several PeuHsfs were tissue-specific expression. Compared to Arabidopsis, more PeuHsf genes were significantly induced by heat, drought and salt stresses (21, 19 and 22 PeuHsfs, respectively). Our findings are helpful in understanding the distinguished adaptability of P. euphratica to extreme environment and providing a basis for functional analysis of PeuHsfs in the future.