Cell-to-cell communication in vascular morphogenesis.

The plant vascular system consists of two conductive cell types, xylem and phloem, which are both produced by procambial cells. Recently, several novel regulatory mechanisms that control the specification of vascular patterning and differentiation have been uncovered. The non-cell-autonomous TDIF/CLE signalling mediates phloem-xylem cross-talk and cambial maintenance; a flowering-related long-distance signal governs secondary development; and novel genetic players such as LHW regulate vascular morphogenesis. A future challenge is to conflate data on the various genetic, hormonal and other factors to understand the networks underlying vascular tissue formation.