A novel nucleus-encoded, chloroplastic NAD(P)H dehydrogenase is involved in non-photochemical plastoquinone reduction and in the control of state transitions in Chlamydomonas reinhardtii

Frédéric Jans1,2, Emmanuel Mignolet1, Pierre-Alain Houyoux1, Pierre Cardol1,2, Fabrice Franck1 and Claire Remacle2

1Laboratory of Plant Biochemistry and Photobiology and 2Laboratory of Genetics of Microorganisms, Department of Life Sciences, Institute of Plant Biology, B22, University of Liège, 27 Boulevard du Rectorat, 4000-Liège, Belgium

In green microalgae, non-photochemical plastoquinone reduction is important for the regulation of the photosynthetic electron transport chain. This activity is catalyzed by a type II NAD(P)H dehydrogenase. In C. reinhardtii, screening of nuclear genome and EST databases revealed six open reading frames with high similarity to mitochondrial type II NAD(P)H dehydrogenases from higher plants. Analysis of the expression of the six genes using RNA blots suggests a major expression of the NDA2 transcript in Chlamydomonas . Using specific antibodies (gift from G. Peltier, see abstract "A type II NDH dehydrogenase in Chlamydomonas chloroplasts" ), we confirm the chloroplastic localisation of Nda2. In addition, two transformants that are inactivated for the NDA2 expression were isolated by RNAi. In these two mutants, the amount of the Nda2 protein is greatly reduced or absent. The loss of Nda2 is responsible for the absence of non-photochemical reduction of the plastoquinone pool. Moreover, the process of state transitions is affected. Complementary data are presented in the abstract from G. Peltier.

e-mail address of presenting author: frederic.jans@ulg.ac.be