DOF2.1 controls vascular cell proliferation downstream of TMO5/LHW

As plant cells are fixed within their tissue context, a precise control of cell division orientation is crucial to generate complex three-dimensional organs. The transcription factor complex formed by TARGET OF MONOPTEROS5 (TMO5) and LONESOME HIGHWAY (LHW) triggers a change in cell division orientation leading to radial expansion, at least in part by activating local cytokinin biosynthesis. However, it remains unclear how cytokinin controls these oriented cell divisions. Here, we analyzed the transcriptional responses upon simultaneous induction of both TMO5 and LHW in detail. Using inferred network analysis, we identify AT2G28510/DOF2.1 as a cytokinin-dependent downstream target gene of the TMO5/LHW heterodimer complex. We further show that DOF2.1 is specifically required and sufficient for vascular cell proliferation without inducing other cytokinin-dependent effects such as the inhibition of vascular differentiation. In summary, we have identified DOF2.1 as a TMO5/LHW target gene, specifically responsible for controlling vascular cell proliferation leading to radial expansion. 4-day-old pRPS5A::TMO5:GR x pRPS5A::LHW:GR (dGR) plants grown on MS were treated with dexamethasone (DEX) compounds for the indicated time, whereafter root meristems were harvested, and total RNA was isolated that was subjected to gene expression profiling.