a, Schematic workflow for the discovery of “cambium TFs”. Cells marked by pARR15::GFP were isolated from roots at three stages of cambium development and used for genome-wide transcript profiling. Candidate cambium TFs were selected based on the “meta-analysis”: an initial 25 TFs were identified based on a combination of two bioinformatic methods, Differentially Expressed Genes (DEG) and Module analysis (shown as Venn diagram), followed by an analysis which added homologues of the initial TFs and cytokinin-induced TFs to obtain a candidate list of 41 TFs (Supplementary Note; Supplementary Table 2). After experimental validation (shown in b), the list of 32 “cambium TFs” were obtained. b, Radial expression patterns of a subset of cambium TFs. Cross sections of the transcriptional GUS reporter line in 1-2 week old roots (left) and RNA in situ hybridisation in 5-week old roots (right) were displayed are shown for each gene. The primary xylem axis is marked in red on the GUS sections. Black arrow-heads indicate the in situ signals. In pLBD4::nYFP-GUS, nYFP-GUS refers to Nuclear Localization Sequence tagged eYFP-GUS. All GUS staining was repeated at least three times with similar results. For in situ hybridisation, at least 10 Col (wild type) plants were examined for each gene with similar patterns. Scale bars, 100µm.