A novel system for xylem cell differentiation in Arabidopsis thaliana

During vascular development, procambial and cambial cells give rise to xylem and phloem cells. Because the vascular tissue is deeply embedded, it has been difficult to analyze the processes of vascular developmen in detail. Here, we establish a novel in vitro experimental system, in which vascular development is induced in Arabidopsis thaliana leaf-disk cultures using bikinin, an inhibitor of glycogen synthase kinase 3 proteins. Transcriptome analysis reveals that mesophyll cells in leaf disks synchronously turn into procambial cells and then differentiate into tracheary elements. Leaf-disk cultures from plants expressing the procambial cell markers TDR_pro:GUS and TDR_pro:YFP can be used for spatiotemporal visualization of procambial cell formation. Further analysis with the tdr mutant and TDIF indicates that the key signaling TDIF- TDR-GSK3s regulates xylem differentiation in leaf-disk cultures. This new culture system can be combined with the analysis using the rich Arabidopsis material resources including cell-marker lines and mutants, thus offering a powerful tool for analyzing xylem cell differentiation.