Objective  This paper aims to explore the important role of Fraxinus mandshurica phytochrome interaction factors (PIFs) in the process of hormone regulation and abiotic stress response, and provide theoretical basis for revealing the molecular mechanism of Fraxinus mandshurica resistance and formulating forest genetic breeding strategies.

  Method  The FmPIFs gene was cloned from Fraxinus mandshurica, and its gene structure, protein physicochemical properties, conserved motifs, and phylogenetic relationships were analyzed by bioinformatics. The qRT-PCR method was used to analyze the expression patterns of FmPIFs genes in Fraxinus mandshurica in different tissues and under different hormones and stress conditions.

  Result  Five members of FmPIFs gene family of Fraxinus mandshurica were obtained and named as FmPIF1, FmPIF3, FmPIF4, FmPIF7 and FmPIF8. The corresponding proteins were all hydrophilic and unstable proteins, all of which were located in the nucleus. The results of multiple sequence alignment showed that FmPIFs all had APB conserved domains, and members FmPIF1 and FmPIF3 had unique APA domains. Tissue-specific analysis showed that FmPIFs were all expressed in leaves at the highest level, and member FmPIF8 expressed at the highest level, which was 3.96 times of control. However, it was expressed in a small amount in the stem, and the highest expression in stem was FmPIF3, which was only 0.21 time of control. The expression in root was extremely low. Stress response analysis showed that FmPIFs positively regulated the resistance of Fraxinus mandshurica plants to salt, alkali and drought stress, while negatively regulated plant cold resistance. The member FmPIF3 responded significantly to cold and salt stress, and the expression of FmPIF8 was significantly up-regulated under alkali stress, the expression of FmPIF1 was significantly up-regulated under drought stress. In the hormone response results, FmPIFs hadrelatively consistent responses to abscisic acid (ABA), salicylic acid (SA) and gibberellin (GA₃), while responses to auxin (IAA) and methyl jasmonate (MeJA) existed difference. FmPIF1 responded violently after MeJA application and its expression was significantly up-regulated, FmPIF7 was significantly up-regulated after SA treatment, and FmPIF3 and FmPIF4 were significantly up-regulated after GA₃ treatment.

  Conclusion  FmPIFs show high consistency in gene and protein structure. RT-qPCR results show that FmPIFs express the highest amount in the leaves of Fraxinus mandshurica. FmPIFs are induced to express by salt, alkali, drought and cold stress, and most of the expression patterns are similar. FmPIFs also play an important role in the regulation of Fraxinus mandshurica in response to IAA, ABA, MeJA, SA and GA₃ hormones.