Issue Date: April 23, 2007
Building barriers in roots
When root cells soak up nutrients from the soil, a single layer of cells called the endodermis (indicated by white arrows) acts as the quality-control barrier. This cellular layer forms a tight seal, somewhat analogous to the blood-brain barrier, that permits transport of ions from the soil into the plant but "prevents potentially toxic compounds from reaching the plant vasculature," says Philip N. Benfey, a biologist at Duke University. Benfey and colleagues have just figured out how this tissue roadblock is formed and maintained (Science 2007, 316, 421). A protein transcription activator called SHORTROOT (SHR, shown in green) is made in the center of a root and transported outward from cell to cell until it reaches the endodermis. There SHR meets its match: a protein called SCARECROW that sequesters SHR and prevents its further movement. Stuck in the endodermis, SHR interacts with other transcription factors to activate genes that uniquely define the endodermis. The work may provide molecular insight on how tissue boundaries are formed in multicellular organisms.
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