Cytoplasmic kinase and phosphatase activities can induce PsaF gene expression in the absence of functional plastids: evi
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O R I GI N A L P A P E R
M. R. Chandok á S. K. Sopory á R. OelmuÈller
Cytoplasmic kinase and phosphatase activities can induce PsaF gene expression in the absence of functional plastids: evidence that phosphorylation /dephosphorylation events are involved in interorganellar crosstalk Received: 29 May 2000 / Accepted: 10 September 2000 / Published online: 14 December 2000 Ó Springer-Verlag 2000
Abstract PsaF is a nuclear gene for subunit III of the reaction center of photosystem I, and its expression is stimulated by cytokinins and light, when monitored at the mRNA level or at the level of GUS activity directed by chimeric promoter::uidA gene fusions in transgenic tobacco. These inductive eects can be mimicked by pertussis toxin, serotonin, phorbol acetate myristate or Ca2+, suggesting the involvement of heterotrimeric G proteins, phospholipids and Ca2+-dependent processes. Both breakdown products of the phosphatidylinositol cycle, inositol triphosphate (IP3) and diacylglycerol (or its homolog phorbol myristate acetate, PMA) appear to be involved. The IP3-dependent pathway requires kinase activity, and the signal operates via a 42-bp Ca2+-responsive element located between positions )220 and )178, while the PMA-dependent pathway requires phosphatase activity and a binding element that lies further upstream in the promoter. The eects of G proteins, phospholipids and Ca2+ on GUS gene expression are restricted to tissues with functional plastids, while modulation of phosphatase and kinase activities activates the responsive PsaF promoter regions even in photobleached material. Thus, activation of kinases and phosphatases can bypass the plastid-mediated inhibition of PsaF gene expression in tobacco seedlings. One cytoplasmic target which re¯ects the functional state of the plastids is protein kinase C. The enzyme can be efCommunicated by R. Hagemann M. R. Chandok á R. OelmuÈller (&) Institut fuÈr Allgemeine Botanik, Lehrstuhl fuÈr P¯anzenphysiologie der Friedrich-Schiller-UniversitaÈt Jena, Dornburger Str. 159, 07743 Jena, Germany E-mail: [email protected] Tel.: +49-3641-949231 Fax: +49-3641-949232 S. K. Sopory International Centre for Genetic Engeneering and Biotechnology, NII Campus, New Delhi 110067, India
®ciently phosphorylated in protein extracts from seedlings in which plastid function is impaired, but not in extracts from green tissue. Key words Plastid signal á Photosynthesis á PsaF á Protein kinase C
Introduction Plastids are semiautonomous organelles and the majority of their polypeptides are encoded in the nucleus, translated on cytoplasmic ribosomes and imported into the organelle. Expression of these genes is controlled by a variety of signals, of which light and cytokinins are the best characterized (Neuhaus et al. 1993; Bowler and Chua 1994; Bowler et al. 1994; Quail 1994; Mustilli and Bowler 1997; Cashmore 1998; Kusnetsov et al. 1994, 1999 and references therein). However, investigations in many laboratories have demonstrated that expression of a large number of nuclear genes required
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