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

Abstract

SUMMARYIntercellular signaling through trafficking of regulatory proteins is a widespread phenomenon in plants and can deliver positional information for the determination of cell fate. 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/INDETER-MINATE DOMAIN proteins, restricts movement of SHR 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 movement from ground tissue to vasculature. Away from the meristem, SCL23 displays long-range rootward movement into meristematic vasculature and a bidirectional radial spread, respectively. As a known target of SHR and SCR, SCL23 also interacts with SCR and SHR and can restrict intercellular outspread of SHR without relying on nuclear retention as SCR does. Collectively, our data show that SCL23 is a mobile protein that controls movement of SHR and acts redundantly with SCR to specify endodermal fate in the root meristem.

Auxin response cell-autonomously controls ground tissue initiation in the early Arabidopsis embryo

“…In addition, it provides a selective barrier for nutrients and acts as a major storage tissue in many plants (1)(2)(3). In Arabidopsis, an elaborate regulatory network has been established for the asymmetric divisions within the ground tissue that give rise to the two ground tissue cell types in the root: endodermis and cortex (4)(5)(6)(7)(8)(9)(10). This network revolves around the central transcriptional regulator SHORT-ROOT (SHR) that moves from the stele into the ground tissue where it is required in the nucleus to maintain endodermis identity and promote asymmetric division in the daughter cells of the ground tissue stem cells to generate separate endodermis and cortex layers (4)(5)(6)(7)(8)(9)(10).…”

“…In Arabidopsis, an elaborate regulatory network has been established for the asymmetric divisions within the ground tissue that give rise to the two ground tissue cell types in the root: endodermis and cortex (4)(5)(6)(7)(8)(9)(10). This network revolves around the central transcriptional regulator SHORT-ROOT (SHR) that moves from the stele into the ground tissue where it is required in the nucleus to maintain endodermis identity and promote asymmetric division in the daughter cells of the ground tissue stem cells to generate separate endodermis and cortex layers (4)(5)(6)(7)(8)(9)(10). The nuclear retention of SHR depends on the activity of SCARECROW (SCR) and the BIRD family of transcription factors that are required to maintain ground tissue identity postembryonically (4,6,(8)(9)(10).…”

“…This network revolves around the central transcriptional regulator SHORT-ROOT (SHR) that moves from the stele into the ground tissue where it is required in the nucleus to maintain endodermis identity and promote asymmetric division in the daughter cells of the ground tissue stem cells to generate separate endodermis and cortex layers (4)(5)(6)(7)(8)(9)(10). The nuclear retention of SHR depends on the activity of SCARECROW (SCR) and the BIRD family of transcription factors that are required to maintain ground tissue identity postembryonically (4,6,(8)(9)(10). In addition, SCR and the heat shock transcription factor SCHIZORIZA (SCZ) regulate asymmetric cell divisions within the ground tissue (11,12).…”

Cell-Fate Specification in Arabidopsis Roots Requires Coordinative Action of Lineage Instruction and Positional Reprogramming

“…S1). Following the periclinal division, both SHR and SCR are thought be essential for determining the endodermal cell fate (Nakajima et al, 2001;Heidstra et al, 2004;Heo et al, 2011;Levesque et al, 2006;Cui et al, 2007;Long et al, 2015aLong et al, , 2015b.…”

“…However, most known regulators in the SHR pathway, such as SCR and BIRD family of zinc finger proteins, appeared to participate in the SHR-SCR feedback loop to restrict the functional scope of SHR to the CEID and its derivative endodermis (Cui et al, 2007;Long et al, 2015aLong et al, , 2015bWelch et al, 2007;Moreno-Risueno et al, 2015). An elegant model was also proposed to explain how SHR function is integrated with auxin signaling to provide spatial information for the periclinal division (Cruz-Ramírez et al, 2012).…”