Practice question

SHORT ROOT and SCARECROW are GRAS family transcription regulators establishing radial ground tissue pattern in Arabidopsis root meristem. SHR protein synthesized exclusively in stele moves via plasmodesmata into adjacent endodermal layer where it activates SCR transcription and forms SHR-SCR heterodimer that sequesters SHR preventing further movement. Complex triggers asymmetric periclinal division producing inner endodermis and outer cortex. Downstream IDD, MAGPIE, and SCL3 targets direct differentiation. Loss of either abolishes formative division, radial organization collapses, emphasizing mobile transcription factor mechanism converting positional signals into concentric tissue architecture surrounding vascular cylinder.