Hormonal control of the molecular networks guiding vascular tissue development in the primary root meristem of Arabidopsis thaliana.

Vascular tissues serve a dual function in plants providing both physical support as well as controlling the transport of nutrients, water, hormones and other small signaling molecules. Xylem tissues transport water from root to shoot; phloem tissues transfer photosynthates from shoot to root; while divisions of the (pro)cambium increase the number of xylem and phloem cells. Although vascular development constitutes a continuous process from primary growth in the early embryo and meristem regions to secondary growth in the mature plant organs, it can be artificially separated into distinct processes including cell type specification, proliferation, patterning and differentiation. In this review, we focus our attention to how hormonal signals orchestrate the molecular regulation of vascular development in the Arabidopsis thaliana primary root meristem. Although auxin and cytokinin have taken center stage in this aspect since their discovery, other hormones including brassinosteroids, abscisic acid and jasmonic acid are also taking up leading roles during vascular development. All these hormonal cues synergistically or antagonistically participate in the development of vascular tissues, forming a complex hormonal control network.