The BZR1-interacting WD repeat protein participates in brassinosteroid-dependent growth and stress response in tomato.

Brassinosteroids (BRs) are steroidal phytohormones that play crucial roles in plant growth and resilience. The stability of BRASSINAZOLE RESISTANT 1 (BZR1), the central transcription factor of BR signaling, is controlled by the GSK3-like kinase BRASSINOSTEROID INSENSITIVE 2 (BIN2)-dependent phosphorylation. However, the regulators mediating BZR1 degradation remain elusive. Here, we identify a BZR1-interacting WD40-repeat protein (BIW) that facilitates ubiquitination and degradation of BZR1 in tomato (Solanum lycopersicum). Mutations in BIW lead to growth phenotypes similar to those of plants with elevated BR signaling, accompanied by enhanced chilling tolerance, whereas overexpressing BIW results in the opposite phenotypes and reduced chilling tolerance. Furthermore, phosphorylation of BIW at Ser144 by BIN2 is essential for its stability and activity. Our findings demonstrate that BIW is an integral component of BR signaling and represents a potential target for genetic modification aimed at improving resilience and productivity.