ON THE COVER

Wood is a specialized tissue in forest tree species and plays a major role in sustaining our economy and ecosystem, but the genetic regulation underlying wood formation remains largely unknown. Integrating a series of transcriptome and transregulation analyses in wood forming cells and transgenic Populus trichocharpa, Chen et al. (pages 602–626) unravel a transcription factor (TF) PtrSND1-B1-mediated transcriptional regulatory network. PtrSND1-B1 mediates 57 TF-DNA and 9 TF-TF (protein-protein) interactions through 17 TFs in a 4-layer regulatory hierarchy for transregulating 27 effector genes for wood formation. All of these protein-protein interactions and 55 of the 57 TF-DNA interactions are newly discovered wood formation-specific interactions. The cover image shows a transverse section of stem wood from 6-month-old green-house-grown P. trichocarpa. Photo by Ilona Peszlen, North Carolina State University.