Ectopic expression of PtrLBD39 inhibited primary and secondary growth in Populus trichocarpa

The primary and secondary growth of trees significantly impacts their biomass and potential applications in timber, pulp, and energy. This growth is regulated by transcription factors (TFs). Notably, a key TF, PtrLBD39, was identified during tension wood formation, and was mainly expressed in the stem phloem in Populus trichocarpa. Ectopic expression of PtrLBD39 into P. trichocarpa effectively inhibited both primary and secondary growth. In LBD39-overexpressing plants, the RNA-seq, ChIP-seq, weighted gene co-expression network analysis (WGCNA) revealed its direct or indirect regulation of TFs governing vascular tissue development, wood formation, hormonal signaling pathways, and enzymes responsible for wood components. This regulation potentially led to growth inhibition, decreased fibrocyte secondary cell wall thickness, and reduced wood production. Therefore, our study confirms PtrLBD39 as a repressor affecting both primary and secondary growth in P. trichocarpa