Poster: Intracellular Signaling

Abs # 826: Sub-cellular localization of Arabidopsis calcium-dependent protein kinases (CDPK) using CDPK-GFP fusions

Presenter:	Hrabak, Estelle M, emhrabak@cisunix.unh.edu
Authors	Hrabak, Estelle M (A)   Etheridge, Naomi  (A)   Dammann, Christian  (B)   Harper, Jeffrey  (B)
Affiliations:	(A): Dept. of Plant Biology, University of New Hampshire (B): Dept. of Cell Biology, Scripps Research Institute

In Arabidopsis thaliana, the family of calcium-dependent protein kinases (CDPKs) contains 34 genes. Each of these kinases has four domains – a variable N-terminal domain, a kinase catalytic domain, an autoinhibitory domain, and a calcium-binding region containing functional EF hands. Evidence suggests that CDPKs are involved in stress responses such as drought, wounding and cold, however their exact roles in these signaling pathways are undetermined. Although Arabidopsis CDPKs do not contain predicted transmembrane regions, the majority have potential amino-terminal myristoylation motifs which may facilitate membrane association or protein-protein interactions. Myristoylated proteins undergo co-translational attachment of a 14-carbon fatty acid to the amino-terminal glycine. An important part of CDPK activity involves calcium sensing, therefore membrane association of CDPKs may promote closer proximity to sites of calcium storage and cytoplasmic influx important in controlling cytoplasmic calcium levels. In an effort to understand the function of CDPKs in Arabidopsis we have determined the sub-cellular localization of more than half of the Arabidopsis CDPKs using transgenic plants over-expressing CDPK-GFP fusions visualized with confocal laser scanning microscopy. Our results revealed membrane association for all CDPKs with a predicted N-terminal myristoylation site. We provide evidence for differential targeting of CDPKs to at least five different subcellular locations, including the plasma membrane, ER, peroxisomes, nucleus and cytosol. The implications of these results with respect to calcium-controlled signal transduction pathways are discussed.