Figure 11.

Model of BSS1/BOP1 Function in BR Signaling.

In the absence of BR activation by Brz, BSS1/BOP1 mRNA expression was induced. BSS1/BOP forms homooligomers and binds BIL1/BZR1, preventing the transport of BIL1/BZR1 to the nucleus. Upon stimulation of BR, the BSS1/BOP1 oligomer was reduced to a monomer, allowing BIL1/BZR1 to be transferred to the nucleus and to induce the expression of BR-responsive genes. BSS1/BOP1 must regulate BR signaling tightly to prevent the activation of BIL1/BZR1 and BES1 when plants should repress BR signaling, such as in the absence of BR or when seedlings are grown under light.