TOPLESS mediates brassinosteroid control of shoot boundaries and root meristem development in Arabidopsis thaliana

Shoot and root development in Arabidopsis thaliana are controlled by many factors, one of which is brassinosteroid (BR) signaling.  BR-responsive gene expression is controlled by the BES1 and BZR1 transcription factors.  Using its EAR domain, BES1 binds to the transcriptional repressor TOPLESS (TPL) to activate and repress genes.  Espinosa-Ruiz et al. show genetic evidence for interaction between BES1 and TPL by using the bes1-D mutant that shows a constitutive BR response.  Expression of the tpl-1 mutant reverses the bes1-D phenotype.  CUP-SHAPED COTYLEDON (CUC) genes mark organ boundaries, and both TPL and BES1 repress CUC3 to separate organs.  In the root quiescent center, cell division is tightly regulated.  TPL binds with BES1 in the quiescent center to regulate the division repressor BRAVO.  The BES1-TPL transcription regulation unit controls signals for cell proliferation in the root and shoot.  (Summary by Daniel Czerny) Development 10.1242/dev.143214