The calcium sensor AtCML8 contributes to Arabidopsis plant cell growth by modulating the brassinosteroid signaling pathway.

Calcium signaling plays an essential role in integrating plant responses to diverse stimuli and regulating growth and development. While some signaling components and their roles are well-established, such as the ubiquitous calmodulin (CaM) sensor, plants possess a broader repertoire of calcium sensors. Notably, CaM-like proteins (CMLs) represent a poorly characterized class for which interacting partners and biological functions remain largely elusive. Our work investigates the role of Arabidopsis thaliana CML8 that exhibits a unique expression profile in seedlings. A reverse genetic approach revealed a function of CML8 in regulating root growth and hypocotyl elongation. RNA-seq analyses highlighted CML8 association with the regulation of numerous genes involved in growth and brassinosteroid (BR) signaling. Using co-immunoprecipitation experiments, we demonstrated that CML8 interacts with the BR receptor, BRI1, in planta in a ligand-dependent manner. This finding suggests the existence of a novel regulatory step in the BR pathway, involving calcium signaling.