Auxin Transport Gene, ClPILS6 , Promotes Branching in Transgenic Poplar by Altering Auxin Homeostasis

Cunninghamia lanceolata (Chinese fir) is an important fast‐growing timber species in southern China, and its branching characteristics directly affect timber yield and quality. Within the regulatory network of plant branching, the auxin signaling pathway plays a central regulatory role; however, the specific functions of related genes during lateral bud development in Chinese fir remain poorly characterized. Therefore, a hub gene, ClPILS6 ( PIN‐LIKE6 ), was identified in the lateral buds of Chinese fir. As a member of the auxin transporter family, ClPILS6 is specifically expressed in buds, lacks transcriptional activation activity, and its expression is significantly induced by exogenous IAA. Overexpression (OE) of ClPILS6 significantly promoted lateral branch development and soluble sugar accumulation while altering auxin homeostasis. Furthermore, ClSPL8 (SQUAMOSA promoter binding protein‐like) binds to the promoter of ClPILS6 and represses its transcription. In summary, these findings reveal the important role of ClPILS6 in branching development and provide a significant theoretical basis for molecular breeding improvement in gymnosperms.