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CELL BIOLOGY AND SIGNAL TRANSDUCTION

Defects in the Cytochrome b₆/f Complex Prevent Light-Induced Expression of Nuclear Genes Involved in Chlorophyll Biosynthesis¹

Institut fuer Biologie III, Universitaet Freiburg, D–79104 Freiburg, Germany (N.S., C.F.B.); Institut de Biologie Physico-Chimique, F–75005 Paris, France (O.V.); and Department of Plant and Microbial Biology, University of California, Berkeley, California 94720–3120 (R.D., K.K.N.)

Mutants with defects in the cytochrome (cyt) b₆/f complex were analyzed for their effect on the expression of a subgroup of nuclear genes encoding plastid-localized enzymes participating in chlorophyll biosynthesis. Their defects ranged from complete loss of the cytb₆/f complex to point mutations affecting specifically the quinone-binding Q_O site. In these seven mutants, light induction of the tetrapyrrole biosynthetic genes was either abolished or strongly reduced. In contrast, a normal induction of chlorophyll biosynthesis genes was observed in mutants with defects in photosystem II, photosystem I, or plastocyanin, or in wild-type cells treated with 3-(3'4'-dichlorophenyl)-1,1-dimethylurea or 2,5-dibromo-3-methyl-6-isopropyl benzoquinone. We conclude that the redox state of the plastoquinone pool does not control light induction of these chlorophyll biosynthetic genes. The signal that affects expression of the nuclear genes appears to solely depend on the integrity of the cytb₆/f complex Q_O site. Since light induction of these genes in Chlamydomonas has recently been shown to involve the blue light receptor phototropin, the results suggest that cytb₆/f activity regulates a plastid-derived factor required for their expression. This signaling pathway differs from that which regulates state transitions, since mutant stt7, lacking a protein kinase involved in phosphorylation of the light-harvesting complex II, was not altered in the expression of the chlorophyll biosynthetic genes.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Christoph F. Beck (beck{at}uni-freiburg.de).

Article, publication date, and citation information can be found at www.plantphysiol.org/cgi/doi/10.1104/pp.106.081059.

^* Corresponding author; e-mail beck{at}uni-freiburg.de; fax 49–761–203–2745.

Received March 28, 2006; returned for revision April 25, 2006; accepted April 25, 2006.

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