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The developmental ontogeny of the vascular system (consisting of xylem, phloem and procambium) is poorly understood despite its central role in plant physiology. We show that in the Arabidopsis root meristem, xylem cell lineages are specified early, whereas phloem and procambium are established through a set of asymmetric cell divisions. These divisions require the WOODEN LEG (WOL) gene. The WOL gene encodes a novel two-component signal transducer with an unusual tandem arrangement of two receiver domains. It is expressed specifically in the vasculature from the early stages of embryogenesis on, consistent with a role as a sensor for vascular morphogenesis.
Mähönen et al. (Fri,) studied this question.