Objective To analyze the pressure of selection in the evolution of PLD gene family in the woody model plant Populus trichocarpa, the cis-acting elements in the promoter, the tissue expression characteristics, and the expression pattern under salt stress in order to provide references for mining the role of PtrPLD in abiotic stress.

Method Using Arabidopsis PLD gene family protein sequence alignment to obtain the P. trichocarpa genome homologous gene, and then identify the PtrPLD gene after the conserved domain identification; using the software ClustalW and MEGA to perform the amino acid sequence alignment and systematic evolution analysis of the PtrPLD and AtPLD genes; using MEME, Plant-mPLoc, ExPasy and other software tools to analyze the characteristics of PtrPLD genes and encoded proteins; using Tbtools software to analyze homologous genes and Ka/Ks values; using Plantcare online tools to analyze the cis-acting elements in the promoter of PtrPLD; using Phytozome transcriptome database and qRT-PCR to analyze the PtrPLD tissue expression characteristics; and using qRT-PCR to analyze the PtrPLD response to salt stress in each tissue.

Result The results show that the PtrPLD family can be divided into 2 subfamilies, C2-PLD and PX/PH-PLD, which containing 13 and 3 genes respectively. There are 7 pairs of paralogous genes and the Ka/Ks between them is far less than 1. The promoter region of PtrPLD family genes contains a large number of abiotic stress and hormone response elements, among which the PtrPLDδ4 promoter contains 20 elements. The PtrPLD family of encoded proteins all contain Motif 1-4, and the sequences on the same evolutionary branch of the evolutionary tree are highly conserved. Analysis of the expression characteristics showed that the PtrPLD family genes have specific expression in roots, stems and leaves, and most members are mainly expressed in the roots. Under NaCl stress, the expression level of PtrPLD family genes in the roots, stems and leaves showed a trend of up-down-up within 72 hours.

Conclusion The results show that the PtrPLD family genes play an important role in the response of P. trichocarpa to salt stress. This study will promote the identification of the biological functions of PtrPLD family genes and the mining of genetic resources in response to abiotic stress.