SCARECROW-LIKE23 and SCARECROW jointly specify endodermal cell fate but distinctly control SHORT-ROOT movement

Intercellular signaling through trafficking of regulatory proteins is a widespread phenomenon in plants and can deliver positional information for cell fate determination. In the Arabidopsis root meristem, the cell fate determinant SHORT-ROOT (SHR), a GRAS domain transcription factor, acts as a signaling molecule from the stele to the adjacent layer to specify endodermal cell fate. Upon exiting the stele, SHR activates another GRAS domain transcription factor SCARCROW (SCR) which, together with several BIRD/INDETERMINATE DOMAIN proteins, restricts SHR movement to define a single cell layer of endodermis. Here we report that endodermal cell fate also requires the joint activity of both SCR and its closest homologue SCARECROW-LIKE23 (SCL23). We show that SCL23 protein moves with zonation-dependent directionality. Within the meristem, SCL23 exhibits short-ranged ground-tissue-to-vasculature movement. Away from the meristem, SCL23 displays long-range rootward movement into meristematic vasculature and a bidirectional radial spread, respectively. As a known SHR and SCR target, SCL23 also interacts with SCR and SHR and can restrict SHR intercellular outspread without relying on nuclear retention as SCR does. Collectively, our data show that SCL23 is a mobile protein that controls SHR movement and acts redundantly with SCR to specify endodermal fate in the root meristem. This article is protected by copyright. All rights reserved