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

Abstract

Vascular tissues serve a dual function in plants, both providing physical support and 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 on how hormonal signals orchestrate the molecular regulation of vascular development in the Arabidopsis 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 also take 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.

Keywords: Abscisic acid; auxin; brassinosteroids; cytokinin; jasmonic acid; vascular development.

Figure1. Hormones control the molecular regulation of vascular development in the primary root meristem of Arabidopsis.

A cross-section through a primary root meristem is shown (A) illustrating the known hormones, molecular regulators and their interactions in the phloem (B) and xylem (C) regions. Hormones are indicated in red; dotted lines illustrate mobility of the hormone or molecular regulator. Please note that the presence and locations of some regulators and hormones on the realistic tissue template are not exact to keep the image orderly and due to space limitations. This image also does not represent accurate hormone levels and distributions across the tissue for the same reasons.