Table II Known potential CDPK substrates.a Substrate Substrate Sourceb Sitec CDPKf Speciesg Effecth Refk Metabolism nitrate reductase leaves TLKRTASTPFM "PKI, PKII" spinach inactivating "1,2" nitrate reductase leaves--spinach TLKRTASTPFM AtCPK3 Arabidopsis inactivating "2,3" PEP carboxylase root nodules ? soybean ?I 4 PEP carboxylase leaves PGEKFFSTDAQ maize ?i 5 PSII reaction center protein D1 peptide ? Spirodela activating?j 6 sucrose-phosphate synthase leaves RMRRISSVEMM PKI spinach inactivating "1,7" sucrose synthase recombinant--mung bean RLTRVHSLRER nodule CDPK soybean higher sucrose affinity 8 sucrose synthase 2 leaves VLSRLHSVRER maize "localization, activating" "9,10" sucrose synthase (nodulin-100) root nodules RLTRVHSLRER soybean localization 11 Stress-related Proteins two-component pseudo-response regulator leaves ? McCDPK1 ice plant ? 12 PAL recombinant--poplar SRVAKTRTLTTAd AtCPK1 Arabidopsis ? 13 PAL "cell cultures, recombinant--poplar" VXKRXLTX French bean lower Vmax 14 Putative Antifungal Proteins Bowman-Birk protease inhibitor Sigma Chemical Co.--soybean RLNSCHSACK embryo CDPK wheat ? 15 g-thionins seeds--yellow mustard KLCQRPSGTWSe embryo CDPK wheat ? 16 lipid transfer proteins "seeds--wheat, barley" XXXPCXS/TYXXG embryo CDPK wheat ? 17 napins seeds--kohlrabi QLQQVISRIYQe embryo CDPK wheat ? 18 potato carboxypeptidase inhibitor potato tuber CWNSARTC embryo CDPK wheat ? 19 Ion/Water Transport aquaglyceroporin nodulin 26 root nodules EITKSASFLKG soybean higher voltage sensitivity "20,21" aquaglyceroporin LIMP2 peptide FITKNVSFLKG Lotus ? 22 aquaporin PM28A peptide AIKALGSFRSN "PKI, PKII" spinach ? 23 Ca2+-ATPase ACA2 recombinant RFTANLSKRYE AtCPK1 Arabidopsis inhibiting 24 PM H+-ATPase roots ? "oat, maize" ? "25,26" potassium channel KAT1 guard cells ? Vicia faba inhibiting "27,28" Other actin-depolymerizing factor cell cultures--maize MANARSGVAV French bean inhibiting?j 29 CDPK-related kinase peptide AALRALSKTLT DcCPK1 carrot ? 30 myosin light chain Chara ? Chara ? 31 PI 4-kinase activator cell cultures ? carrot activation of PI 4-kinase 32 proteasome regulatory subunit homologue peptide ? NtCDPK1 N. tabacum ? 33 self-incompatibility RNases style ? pollen tube Nak-1 N. alata ? 34 serine acetyltransferase cell cultures ? soybean reduces feedback inhibition 35 "aPotential substrates included are those convincingly shown to be phosphorylated, in vivo or in vitro, in a calcium-stimulated manner by a CDPK (rather than CaMK). In vivo data is not available in many cases. For some substrates, results for only particular species are reported due to space constraints. b The source of the substrate used in the studies, including the organism if different from that of the CDPK. cThe amino acid phosphorylated by the CDPK is underlined, if known, and the surrounding amino acids are shown. dPAL is phosphorylated on one of the threonines in this sequence. eCDPKs phosphorylate many proteins in this class. A site for only one protein is shown. fName of the CDPK or tissue source, if different from that of the substrate. gThe plant species expressing the CDPK. hEffect of the phosphorylation by CDPK, if known. iCDPKs phosphorylate PEPC on a site important for catalytic activation, but CDPKs do not appear to activate these proteins, suggesting other factors are involved or CDPKs are not the key enzymes in vivo (Ogawa et al., 1998). jPhosphorylation of the designated site is known to be important for the given effect in vivo, but the effect of CDPK phosphorylation has not been demonstrated. k1, McMichael et al., 1995a; 2, Douglas et al., 1997; 3, Douglas et al., 1998; 4, Zhang and Chollet, 1997; 5, Ogawa et al., 1998; 6, Swegle et al., 2001.; 7, McMichael et al., 1995b; 8, Nakai et al., 1998; 9, Huber et al., 1996; 10, Winter et al., 1997; 11, Zhang et al., 1999; 12, Patharkar and Cushman, 2000; 13, Cheng et al., 2001; 14, Allwood et al., 1999; 15, Neumann et al., 1994; 16, Neumann et al., 1996a; 17, Neumann et al., 1993; 18, Neumann et al., 1996b; 19, Neumann et al., 1996c; 20, Weaver and Roberts, 1992; 21, Lee et al., 1995; 22, Guenther and Roberts, 2000; 23, Huang et al., 2001; 24, Hwang et al., 2000; 25, Harmon et al., 1996; 26, Camoni et al., 1998a; 27, Li et al., 1998; 28, Berkowitz et al., 2000; 29, Allwood et al., 2001; 30, Farmer and Choi, 1999; 31, McCurdy and Harmon, 1992."