Chemical Perturbation of Chloroplast Ca Dynamics in Arabidopsis thaliana Suspension Cell Cultures and Seedlings.

Ca signaling is part of universal signal transduction pathways to respond to external and internal stimuli or stress and in plants plays a central role in chloroplasts, such as in the regulation of photosynthetic enzymes or the transition from light to dark. Only recently, the underlying molecular machinery, e.g., transporters and channels that enable chloroplast Ca fluxes, has started to be elucidated. However, chemical tools to specifically perturb these chloroplast Ca fluxes are largely lacking. Here, we describe an efficient aequorin-based system in Arabidopsis thaliana suspension cell cultures to screen for chemicals that alter light-to-dark-induced chloroplast stroma Ca signals. Subsequently, the effect of the hits on chloroplast Ca signals is validated in Arabidopsis seedlings. The research lays a foundation for the identification of novel proteins involved in Ca transport in chloroplast stroma under light-to-dark transition and for investigating the interaction of chloroplast Ca signaling with photosynthesis in general.