Elucidation of Calcium-Signaling Components and Networks

Abstract

Calcium signaling depends on proteins at three nodes: generation of Ca²⁺ signature, sensing of changes in cellular Ca²⁺ level, and transduction of a Ca²⁺ signal. Plant cells have multiple mechanisms for generating increases in [Ca²⁺]_cyt suggesting the capacity to produce complex spatiotemporal patterns of [Ca²⁺] _cyt elevation. A large number of Ca²⁺ sensors have been identified experimentally or have been predicted on the basis of sequence similarity to known Ca²⁺-binding proteins or the presence of Ca²⁺-binding domains. The number of target proteins is expected to be large, as a given sensor can interact with multiple proteins. Proteins involved in Ca²⁺signaling in plants have been identified using Ca²⁺-binding, protein–protein interaction, yeast two-hybrid, and coprecipitation screens. With the completion of genomic sequencing of several plants, researchers have identified many Ca²⁺ sensors and target proteins on a global scale. In Arabidopsis, about 3–4% of the proteome appears to participate in Ca²⁺ signaling. The challenge now is the elucidation of the function of each verified/predicted protein involved in Ca²⁺ signaling on a local and global scale.