Signal transduction of a calcium-dependent protein kinase and its interacting proteins in Mesembryanthemum crystallinum during abiotic stress

McCDPK1 is a salinity- and drought-induced calcium-dependent protein kinase (CDPK) isolated from the common ice plant, Mesembryanthemum crystallinum. A yeast two-hybrid experiment was performed with five different portions of McCDPK1 in an attempt to isolate proteins that interact with McCDPK1. A total of nine different interacting proteins were recovered in this screen. Two of these interacting proteins were characterized in detail. The first, CDPK substrate protein 1 (CSP1), is a substrate for McCDPK1. CSP1 is a member of the two-component pseudo-response regulator gene family. CSP1 is a sequence-specific DNA binding protein containing a well conserved helix-loop-helix DNA binding domain. The second interacting protein, Mesembryanthemum crystallinum CDPK trafficking protein 1 (McCTP1), serves a putative translocation protein for McCDPK1 that helps McCDPK1 achieve a dynamic localization pattern within the cell following abiotic stress. McCTP1 interacts with McCDPK1 both in vitro and in vivo, but is unlikely to serve as a McCDPK1 substrate. McCTP1 and McCDPK1 colocalize to the cytoskeleton and to the nucleus of cells from plants exposed to high salinity and low humidity.