Heat shock protein 90 acts in brassinosteroid signaling through interaction with BES1/BZR1 transcription factor

Brassinosteroids (BRs), a class of phytohormones, control various physiological and developmental processes in plants. Two highly homologous transcription factors, BRASSINOSTEROID INSENSITIVE 1-EMS-SUPRESSOR 1 (BES1) and BRASSINAZOLE RESISTANT 1 (BZR1), act downstream of BR signaling to control several thousands of putative target genes. We reported previously that BES1 forms a complex with a molecular chaperone: heat shock protein 90 (HSP90). This study demonstrates that the aminoterminal and central parts of BES1 are responsible for its physical interaction with HSP90.3 in vitro. Additionally, we present evidence that BZR1 is a novel HSP90 partner aside from two BR signaling components previously identified as its clients: BES1 and BRASSINOSTEROID INSENSITIVE 2 (BIN2). Furthermore, geldanamycin, an inhibitor of ATPase activity in HSP90, caused BES1 hyperphosphorylation and disrupted the expression of BR-responsive genes. Considered together, our results imply that HSP90 takes a part in BR-mediated gene expression through complex formation with two major transcription factors. (C) 2015 Elsevier GmbH. All rights reserved.