A Chinese fir ClWND2B-ClMYB3 transcriptional cascade promotes lignin accumulation during wood formation in poplar

Chinese fir ( Cunninghamia lanceolata ) is an important coniferous wood species, which has the characteristics of fast-growing, desirable timber performance, and strong adaptability. The molecular network of production of wood has been depicted in model species. Nevertheless, the regulatory mechanism governing secondary cell wall (SCW) thickening remains elusive in Chinese fir. Hereby, we identified a hub gene in Chinese fir cambial, ClMYB3, a homolog of poplar PtrMYB3 . As a nuclear protein factor, ClMYB3 exhibited transactivation activity in yeast cells. A series of assays revealed a positive effect of ClMYB3 on Cl4CL by interacting with its promoter. Besides, overexpression (OE) of ClMYB3 significantly promoted the SCW thickening and xylem development. In contrast, its dominant repression (DR) showed the opposite effects in transgenic poplar. Moreover, ClWND2B-4 functioned upstream of ClMYB3 to activate its expression by binding to its promoter. Importantly, ClWND2B-4 -OE lines displayed an overt ectopic deposition of lignin in the SCW of vessel cells. On the contrary, DR lines showed a considerable reduction of lignin accumulation and SCW thickness. Collectively, the results decipher the fine-tuned modulation of SCW formation by the ClWND2B-ClMYB3 module and provide a new perspective for genetic improvement of wood production in Chinese fir. • ClMYB3 acts as a transcriptional activator localized in the nucleus. • ClMYB3 positive regulates lignin deposition in transgenic poplar. • ClMYB3 activates the transcription of Cl4CL by binding to its promoter. • ClWND2B-4 activates ClMYB3 promoter activity to promote wood formation.