DECODING Ca²⁺ SIGNALS THROUGH PLANT PROTEIN KINASES

Plants harbor four families of kinases that have been implicated in Ca²⁺ signaling (CDPKs, CRKs, CCaMKs, and SnRK3s). Although each family appears to respond to Ca²⁺ via different mechanisms, they all utilize Ca²⁺ sensors that bind Ca²⁺ through multiple EF-hands. The CDPK (Ca²⁺-dependent protein kinase) family is represented by the most genes, with 12 subfamilies comprised of 34 isoforms in Arabidopsis and 27 in rice. Some of the calcium-regulated kinases also show potential for regulation by lipid signals and kinase cascades. Thus, Ca²⁺-regulated kinases provide potential nodes of cross-talk for multiple signaling pathways that integrate Ca²⁺ signals into all aspects of plant growth and development.