The vascular system of flowering plants develops from a handful of provascular initial cells in the early embryo into a whole range of different cell types in the mature plant.

In order to account for such proliferation and to generate this kind of diversity, vascular tissue development relies on a large number of highly oriented cell divisions. The transcription factor complex formed by TARGET OF MONOPTEROS5 / LONESOME HIGHWAY (TMO5/LHW) is one of the major regulators of vascular proliferation and oriented cell divisions in the model plant Arabidopsis thaliana.