SCARECROW reinforces SHORT-ROOT signaling and inhibits periclinal cell divisions in the ground tissue by maintaining SHR at high levels in the endodermis

In contrast to development in animals, much of the patterning of plants occurs post-embryonically in specialized structures called meristems. The root apical meristem of Arabidopsis thaliana is a readily accessible structure that has been extensively studied to uncover the factors that control root growth and cellular patterning. Recently we showed that one of the key factors in patterning the root, the mobile transcription factor SHORT-ROOT (SHR), acts in a concentration-dependent manner to initiate or suppress asymmetric divisions in the endodermis. The amount of SHR varies dynamically in the endodermis with the age of the root. Here we show that this variation is controlled in part through the activity of the transcription factor, SCARECROW (SCR), which regulates SHR movement and therefore its effective concentration and function in the endodermis.