Overexpression of Promotes Growth and Causes Leaf Wrinkle and Branch Appearance in .

D-type cyclin (cyclin D, CYCD), combined with cyclin-dependent kinases (CDKs), participates in the regulation of cell cycle G1/S transition and plays an important role in cell division and proliferation. CYCD could affect the growth and development of herbaceous plants, such as , by regulating the cell cycle process. However, its research in wood plants (e.g., poplar) is poor. Phylogenetic analysis showed that in , genes expanded to six members, namely . genes were amplified based on the CDS region of genes. showed the highest expression in the shoot tip, and the higher expression in young leaves among all members. Therefore, this gene was selected for further study. The overexpression of in plants demonstrated obvious morphological changes during the observation period. The leaves became enlarged and wrinkled, the stems thickened and elongated, and multiple branches were formed by the plants. Anatomical study showed that in addition to promoting the differentiation of cambium tissues and the expansion of stem vessel cells, facilitated the division of leaf adaxial epidermal cells and palisade tissue cells. Yeast two-hybrid experiment exhibited that 12 PtoCDK proteins could interact with PtoCYCD3;3, of which the strongest interaction strength was PtoCDKE;2, whereas the weakest was PtoCDKG;3. Molecular docking experiments further verified the force strength of PtoCDKE;2 and PtoCDKG;3 with PtoCYCD3;3. In summary, these results indicated that the overexpression of significantly promoted the vegetative growth of , and PtoCYCD3;3 may interact with different types of CDK proteins to regulate cell cycle processes.