Small-molecule hormones, including brassinosteroids (BRs) and gibberellins (GAs), influence plant growth and development. Although previous studies suggested that crosstalk occurs between the BR and GA signalling pathways, the mechanisms by which GAs and BRs coordinate to control growth were unclear. Here, Li et al. report that in Arabidopsis thaliana BZR1 (a transcription factor that is activated by BR signalling) interacts with REPRESSOR OF GA1-3 (RGA), a member of the DELLA family of transcriptional regulators, which inhibit the GA signalling pathway. Overexpression of RGA lacking the DELLA domain resulted in a reduction in BZR1, suggesting that DELLAs affect the levels of BZR1. Furthermore, reporter gene assays indicated that BZR1 and RGA antagonize each other's transcriptional activity. Notably, this paper highlights the role of DELLAs as mediators of signalling crosstalk between BRs and GAs in controlling cell elongation and growth.