Systematic Analysis of the Populus ADF Gene Family and the Expression Patterns Under Osmotic Stress

Actin Depolymerizing Factor (ADF) proteins are key regulators of actin cytoskeleton dynamics, mediating numerous essential plant life processes, including cell elongation, division, and signal transduction in response to environmental stress. Although ADF functions are well characterized in herbaceous plants, systematic analysis of poplar ADFs and their roles in osmotic stress response remains largely unexplored. In this study, we identified 14 PtADF genes in the Populus trichocarpa genome, mapped across ten distinct chromosomes. Phylogenetic analysis categorized all the ADFs into seven groups, with PtADFs displaying conserved motifs. PtADF gene family expansion was primarily attributed to whole-genome duplication (WGD) events. Evolutionary constraint analysis, evidenced by a Ka/Ks ratio < 1, indicated significant selective pressure on these genes. Promoter regions of PtADF genes were enriched with cis-acting elements responsive to hormones and stresses. Transcriptome profiling showed that five PtADF genes were significantly induced under drought stress. We then identified the homologous genes of PtADFs in P. euphratica, a Populus species with superior environmental stress adaptability, and qRT-PCR analysis revealed that four homologous PeADFs were significantly induced by mannitol treatment. These results characterize the basic features of the PtADF gene family and provide a general reference for screening candidate PeADF genes for further research in poplar.