Abstract
In a vascular tissue of Arabidopsis roots, specific cell types are arranged in diametrically opposed longitudinal files that maximize the distance between them and create a bilaterally symmetric root. Mutations in the LONESOME HIGHWAY (LHW) gene eliminate bilateral symmetry and reduce the number of cells in the stele of the root, resulting in roots with only single protoxylem and protophloem poles. LHW does not appear to be required for the creation of any specific cell type, but coordinately controls the number of all vascular cell types by regulating the size of the pool of cells. LHW encodes a protein with weak sequence similarity to basic helix-loop helix (bHLH)-domain proteins. Now efforts are underway to reveal how LHW regulates vascular development in roots.
