Abstract text: Trees control the orientation of stems and branches by forming specific tissue structures and cell wall components which generates tension stress. In particular, hardwood species form tension wood (TW) to maintain their postures in response to gravity directions. TW is generally found in the upper side of a bending stem and contains wood fibers with a gelatinous layer inside the secondary cell wall. Although recent studies showed some genes are related to the formation of TW (Xu et al., 2024; Huang et al., 2025), the transcriptional regulation for the formation of tension wood remains not fully understood. Here, we established in vitro induction system of tension wood using Populus tremula × P. tremuloides, T89. Temporal transcriptome data using the induction system successfully revealed the dynamic expression patterns of transcription factor genes associated with the tension wood formation. Generated CRISPR/Cas9 knockout hybrid aspen lines for candidate transcription factor genes suggested the requirement of these genes for TW formation. Together, our results will provide new aspects of the foundation for transcriptional networks controlling tension wood formation.