Organellar calcium signaling in plants: An update

Calcium ion (Ca²⁺) is a versatile signaling transducer in all eukaryotic organisms. In plants, intracellular changes in free Ca²⁺ levels act as regulators in many growth and developmental processes. Ca²⁺ also mediates the cellular responses to environmental stimuli and thus plays an important role in providing stress tolerance to plants. Ca²⁺ signals are decoded by a tool kit of various families of Ca²⁺−binding proteins and their downstream targets, which mediate the transformation of the Ca²⁺ signal into appropriate cellular response. Early interest and research on Ca²⁺ signaling focused on its function in the cytosol, however it has become evident that this important regulatory pathway also exists in organelles such as nucleus, chloroplast, mitochondria, peroxisomes and the endomembrane system. In this review, we give an overview on the knowledge about organellar Ca²⁺ signaling with a focus on recent advances and developments.