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A stress‐induced calcium‐dependent protein kinase from Mesembryanthemum crystallinum phosphorylates a two‐component pseudo‐response regulator
Author(s) -
Patharkar O. Rahul,
Cushman John C.
Publication year - 2000
Publication title -
the plant journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.058
H-Index - 269
eISSN - 1365-313X
pISSN - 0960-7412
DOI - 10.1046/j.1365-313x.2000.00912.x
Subject(s) - mesembryanthemum crystallinum , biology , microbiology and biotechnology , phosphorylation , biochemistry , regulator , response regulator , complementary dna , gene , crassulacean acid metabolism , photosynthesis , mutant
Summary 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, using full‐length McCDPK1 and truncated forms of McCDPK1 as baits, to identify interacting proteins. A catalytically impaired bait isolated a cDNA clone encoding a novel protein, CDPK substrate protein 1 (CSP1). CSP1 interacted with McCDPK1 in a substrate‐like fashion in both yeast two‐hybrid assays and wheat germ interaction assays. Furthermore, McCDPK1 was capable of phosphorylating CSP1 in vitro in a calcium‐dependent manner. Our results demonstrate that the use of catalytically impaired and unregulated CDPKs with the yeast two‐hybrid system can accelerate the discovery of CDPK substrates. The deduced CSP1 amino acid sequence indicated that it is a novel member of a class of pseudo‐response regulator‐like proteins that have a highly conserved helix–loop–helix DNA binding domain and a C‐terminal activation domain. McCDPK1 and CSP1 co‐localized to nuclei of NaCl‐stressed ice plants. Csp1 transcript accumulation was not regulated by NaCl or dehydration stress. Our results strongly suggest that McCDPK1 may regulate the function of CSP1 by reversible phosphorylation.