PLOS Genetics study identifies BBX5 as a positive regulator of shade avoidance via PIF4 and auxin pathways in plants

A study published in *PLOS Genetics* on 5 June 2026 by Fengyue Zhao, Rongbo Yang, Zhaoqing Song, and colleagues identifies B-box PROTEIN 5 (BBX5) as a positive regulator of the shade avoidance response in plants.

Shade avoidance is triggered when plants detect changes in light quality — specifically a reduced ratio of red to far-red light — caused by neighbouring vegetation. The phytochrome B (phyB)–PHYTOCHROMEINTERACTING FACTOR 4 (PIF4) module is a well-established central regulatory hub in this response. The new work places BBX5 within this network: phyB interacts with BBX5 and promotes its protein stability under appropriate light conditions, while the E3 ubiquitin ligase COP1 (CONSTITUTIVELY PHOTOMORPHOGENIC 1) acts in the opposing direction. BBX5, in turn, activates PIF4 transcription and also upregulates genes involved in auxin biosynthesis and signalling, linking the light-quality signal to downstream growth responses characteristic of shade avoidance.

The findings contribute to understanding how multiple regulatory inputs are integrated at the chromatin level to coordinate developmental responses to the light environment. The research has implications for plant biology, agricultural genomics, and the study of gene regulatory networks. It does not have direct clinical relevance.