title: Calcium and calmodulin are involved in blue light induction of the gsa gene for an early chlorophyll biosynthetic step in Chlamydomonas.
abstract: The Chlamydomonas reinhardtii nuclear gene gsa, which encodes the early chlorophyll biosynthetic enzyme glutamate 1-semialdehyde aminotransferase (GSAT), is specifically induced by blue light in cells synchronized in a 12-hr-light and 12-hr-dark regime. Light induction required the presence of a nitrogen source in the incubation medium. Maximal induction also required acetate. However, in the absence of acetate, partial induction occurred when Ca2+ was present in the medium at concentrations of > or = 1 microM. The Ca2+ channel-blocking agents Nd3+ and nifedipine partially inhibited the external Ca(2+)-supported induction of GSAT mRNA but did not inhibit acetate-supported induction. The calmodulin antagonists trifluoperazine and N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide inhibited both external Ca(2+)-supported and acetate-supported induction. The Ca2+ ionophore A23187 caused a transient induction in the dark. These results suggest that Ca2+ and calmodulin are involved in the signal transduction pathway linking blue light perception to the induction of GSAT mRNA. The electron transport uncoupler carbonyl cyanide m-chlorophenylhydrazone inhibited acetate-supported induction of GSAT mRNA but did not inhibit external Ca(2+)-supported induction. It is proposed that in the presence of acetate, an internal pool of Ca2+ can be mobilized as a second message, whereas in the absence of acetate, internal Ca2+ is not available but the requirement for Ca2+ can be partially met by an external Ca2+ source. The mobilization of internal Ca2+ may require energy derived from metabolism of acetate.
authors.affiliation: Division of Biology and Medicine, Brown University, Providence, Rhode Island 02912, USA.
authors.forename: C S
authors.initials: CS
authors.lastname: Im
authors.forename: G L
authors.initials: GL
authors.lastname: Matters
authors.forename: S I
authors.initials: SI
authors.lastname: Beale
mesh_terms: D000085:Acetates / Q000378:metabolism / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology; D002121:Calcium Channel Blockers / Q000494:pharmacology; D002147:Calmodulin / Q000378:metabolism*; D016825:Chlamydomonas reinhardtii / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism*; D002734:Chlorophyll / Q000096:biosynthesis*; D004790:Enzyme Induction / Q000187:drug effects; D017343:Genes, Plant; D019751:Intramolecular Transferases; D007535:Isomerases / Q000096:biosynthesis*; D008027:Light; D008274:Magnesium / Q000494:pharmacology; D009354:Neodymium / Q000494:pharmacology; D009543:Nifedipine / Q000494:pharmacology; D013449:Sulfonamides / Q000494:pharmacology
chemical_list: D000085:Acetates; D002121:Calcium Channel Blockers; D002147:Calmodulin; D013449:Sulfonamides; D002734:Chlorophyll; D009354:Neodymium; C017967:W 7; C034700:N-(6-aminohexyl)-1-naphthalenesulfonamide; D007535:Isomerases; D019751:Intramolecular Transferases; C061049:glutamate-1-semialdehyde 2,1-aminomutase; D008274:Magnesium; D009543:Nifedipine; D002118:Calcium