Diffusible repression of cytokinin signalling produces endodermal symmetry and passage cells

[摘要] In vascular plants, the root endodermis surrounds the central vasculature as a protective sheath that is analogous to the polarized epithelium in animals, and contains ring-shaped Casparian strips that restrict diffusion(1). After an initial lag phase, individual endodermal cells suberize in an apparently random fashion to produce 'patchy' suberization that eventually generates a zone of continuous suberin deposition(2). Casparian strips and suberin lamellae affect paracellular and transcellular transport, respectively. Most angiosperms maintain some isolated cells in an unsuberized state(3) as so-called 'passage cells', which have previously been suggested to enable uptake across an otherwise impermeable endodermal barrier(3,4). Here we demonstrate that these passage cells are late emanations of a meristematic patterning process that reads out the underlying non-radial symmetry of the vasculature. This process is mediated by the non-cell-autonomous repression of cytokinin signalling in the root meristem, and leads to distinct phloem- and xylem-pole-associated endodermal cells. The latter cells can resist abscisic acid-dependent suberization to produce passage cells. Our data further demonstrate that, during meristematic patterning, xylem-pole-associated endodermal cells can dynamically alter passage-cell numbers in response to nutrient status, and that passage cells express transporters and locally affect the expression of transporters in adjacent cortical cells.

[关键词] TRANSCRIPTION FACTOR;ARABIDOPSIS;ROOTS;AUXIN;DIFFERENTIATION;TRANSDUCTION;MERISTEM;SYSTEM;PHO1