Inner voices meet outer signals: The plasticity of rhizodermic cells

In contrast to animals, post-embryonic development of plants is highly plastic. This necessitates the integration of internal and external signals to allow for a rapid adjustment of developmental programs according to the prevailing conditions. A prime example of such plasticity are rhizodermic cells, in which function and fate results from an array of information. Root epidermal cells can develop into either a root hair cell or a non-hair cell, following a pattern that is genetically determined, but also responsive to environmental cues. The decision of an epidermal cell to form a hair is dependent on bidirectional signaling circuits among neighboring cells and on positional information from the underlying tissue. In addition, environmental signals are perceived and integrated into the cell specification process and may interact with, or overrule intrinsic programs. Root epidermal cells therefore represent a well-explored model to study how graded information is translated into binary decisions.