B-BOX DOMAIN PROTEIN28 Negatively Regulates Photomorphogenesis by Repressing the Activity of Transcription Factor HY5 and Undergoes COP1-Mediated Degradation

Abstract

Plants have evolved a delicate molecular system to fine-tune their growth and development in response to dynamically changing light environments. In this study, we found that BBX28, a B-box domain protein, negatively regulates photomorphogenic development in a dose-dependent manner in <i>Arabidopsis thaliana</i> BBX28 interferes with the binding of transcription factor HY5 to the promoters of its target genes through physical interactions, thereby repressing its activity and negatively affecting HY5-regulated gene expression. In darkness, BBX28 associates with CONSTITUTIVELY PHOTOMORPHOGENIC1 (COP1) and undergoes COP1-mediated degradation via the 26S proteasome system. Collectively, these results demonstrate that BBX28 acts as a key factor in the COP1-HY5 regulatory hub by maintaining proper HY5 activity to ensure normal photomorphogenic development in plants.