Tree peony is a popular traditional flower, which is known as the king of flowers in China. Relatively poor in vitro rooting has limited the its large-scale commercial production. In this study, a transcriptome sequencing analysis was performed to screen and identify DEGs and the associated metabolic pathways at different stages of tree peony root development under sandy loam cultivation. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses revealed many of the DEGs were involved in auxin metabolism. Which proved that auxin and the related genes were revealed to be important for the induction and formation of roots in tree peony. Then we screened and verified their functions of the rooting-related genes PsIAA27 and PsARF19. The qRT-PCR analysis and functional verification indicated that the expressions of PsARF19 and PsIAA27 in tree peony seedlings, cuttings and grafted seedlings were significant different. PsARF19 promoted root development, it might be a regulatory gene related to the formation of tree peony roots, while PsIAA27 inhibited lateral root development, and it might be involved in controlling auxin sensitivity during root formation. The results of this study may form the basis of future investigations on the mechanism mediating peony root formation. The transcriptome data will be an excellent resource for researchers interested in characterizing the rooting-related tree peony genes.
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