Calcium-mediated signal transduction in plants: A perspective on the role of Ca2+ and CDPKs during early plant development

In plants, calcium acts as a second messenger in the regulation of a variety of physiological and metabolic processes. For signal transduction via calcium, transient and often local elevations in the level of cytosolic Ca2+ must occur. This requires a well-controlled co-operation of tightly regulated Ca2+-channels and active Ca2+-transporters such as primary Ca2+-ATPases and the H+/Ca2+ antiporters found both at the plasma membrane and endomembranes. Downstream events in calcium signaling involve Ca2+-binding proteins and protein kinases that sense, amplify and transduce the Ca2+-signal further downstream. This review gives an overview of the Ca2+-messenger system and its components in plants. Although endosperm development, embryogenesis and germination are dynamic and intriguing developmental processes in the life cycle of plants, very little is known about the signaling events that regulate them. Recent observations suggest the involvement of Ca2+-mediated signaling and Ca2+-dependent protein kinases during these early-developmental processes in plants. A perspective of Ca2+-signaling during seed development and germination is presented.