Figure 1.

SCR activates first, but represses subsequent, asymmetric cell divisions in the Arabidopsis root. (A) Schematic depicting the spatial distribution of SHR/SCR and SCR/LHP1 complexes along the longitudinal axis of the Arabidopsis root. The ratio between SCR/SHR is low in CEI, favoring formation of the SHR/SCR activator complex; the ratio would increase rapidly due to SHR/SCR dependent positive feedback regulation of SCR transcription and, above a certain threshold the SCR/LHP1 complex will dominate, thus turning SCR into a repressor. CEI, cortex/endodermis initial cell; Cor, cortex; End, endodermis. (B) in situ hybridization showing the expression pattern of MGP, a common target of SCR and LHP1.