The transcriptional regulator BBX24 impairs DELLA activity to promote shade avoidance in Arabidopsis thaliana

Abstract

In response to canopy shade, plant vegetative structures elongate to gain access to light.However, the mechanism that allows a plastic transcriptional response to canopy shade lightis not fully elucidated. Here we propose that the activity of PIF4, a key transcription factor inthe shade signalling network, is modulated by the interplay between the BBX24 transcriptionalregulator and DELLA proteins, which are negative regulators of the gibberellin (GA)signalling pathway. We show that GA-related targets are enriched among genes responsive toBBX24 under shade and that the shade-response defect in bbx24 mutants is rescued by a GAtreatment that promotes DELLA degradation. BBX24 physically interacts with DELLA proteinsand alleviates DELLA-mediated repression of PIF4 activity. The proposed molecularmechanism provides reversible regulation of the activity of a key transcription factor that mayprove especially relevant under fluctuating light conditions.