Cloning and salt tolerance analysis of the PnHB7 transcription factor in Populus nigra L

HD-Zip transcription factors play an important role in regulating plants' response to salt stress, but there have been few studies of HD-Zip transcription factors in poplar and their role in salt-stress responses. In this study, the PnHB7 was cloned from Populus nigra L., a bioinformatics analysis was conducted, and a genetic transformation vector was constructed. The results show that PnHB7 was a transcription factor belonging to the HD-Zip family I subfamily, located on chromosome 14, with a length of 717 bp, encoding 238 amino acids, a molecular formula of C1185H1861N329O387S8. Multiple cis-acting elements related to stress response are contained in the upstream promoter region. Subcellular localization showed that the PnHB7:GFP fusion protein was located in the nucleus. Under a 0.4 % NaCl treatment, the growth and physiological indexes of overexpressed tobacco (Nicotiana tabacum L.) were better than those of wild-type tobacco, and salt tolerance was higher. The stress responses of tobacco seedlings transformed by 35S:pro-PnHB7:GUS showed that PnHB7 responded to abscisic acid, ethylene, methyl jasmonate, and NaCl stress. The transcriptome sequencing results of overexpressed tobacco showed that hormone-related protein genes (abscisic acid, gibberellin, ethylene, salicylic acid), oxidase genes (oxygenase, peroxidase, polyphenol oxidase) and transcription factor protein genes were significantly upregulated, and most were located in the signal pathway of ABA transduction. It is speculated that PnHB7 plays an important role in the ABA regulation pathway.