Abstract

(1) Background: Lignin is a unique component of the secondary cell wall, which provides structural support for perennial woody plants.ARFsare the core factors of the auxin-signaling pathway, which plays an important role in promoting plant growth, but the specific relationship between auxin response factors(ARFs)and lignin has not been fully elucidated with regard to rapid plant growth in forest trees. (2) Objectives: This study aimed to investigate the relationship betweenARFsand lignin with regard to rapid plant growth in forest trees. (3) Methods: We used bioinformatics analysis to investigate thePyuARFfamily, find genes homologous toARF6andARF8inPopulus yunnanensis, and explore the changes in gene expression and lignin content under light treatment. (4) Results: We identified and characterized 35PyuARFsbased on chromosome-level genome data fromP. yunnanensis. In total, we identified 92ARFgenes inP. yunnanensis,Arabidopsis thaliana, andPopulus trichocarpa, which were subsequently divided into three subgroups based on phylogenetic analysis and classified the conserved exon–intron structures and motif compositions of theARFsinto the same subgroups. Collinearity analysis suggested that segmental duplication and whole-genome duplication events were majorly responsible for the expansion of thePyuARFfamily, and the analysis of Ka/Ks indicated that the majority of the duplicatedPyuARFsunderwent purifying selection. The analysis of cis-acting elements showed thatPyuARFswere sensitive to light, plant hormones, and stress. We analyzed the tissue-specific transcription profiles ofPyuARFswith transcriptional activation function and the transcription profiles ofPyuARFswith high expression under light in the stem. We also measured the lignin content under light treatment. The data showed that the lignin content was lower, and the gene transcription profiles were more limited und