Plants cells cannot migrate, so plants control the development of multilayered tissues such as roots through asymmetric cell divisions that create layers with different identities and functions.

A team headed by Athanasius Marée of the John Innes Centre in Norwich, UK, and Ben Scheres at the University of Utrecht in the Netherlands unravelled the molecular pathway that regulates these cell divisions in the root tip. Stem cells in the model plant Arabidopsis are triggered to divide unevenly by a positive feedback loop that takes effect when a protein called RETINOBLASTOMA ceases to inhibit another, called SCARECROW. Gradients of a growth hormone and a protein called SHORT ROOT ensure that this loop is triggered in the correct place. Protein degradation during the division prevents the process from continuing indefinitely.

Cell (2012)