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First published online July 28, 2006; 10.1104/pp.106.082982 Plant Physiology 142:333-342 (2006) © 2006 American Society of Plant Biologists The Plant-Like C2 Glycolate Cycle and the Bacterial-Like Glycerate Pathway Cooperate in Phosphoglycolate Metabolism in Cyanobacteria1Universität Rostock, Institut Biowissenschaften, Pflanzenphysiologie, D–18051 Rostock, Germany (M.E., D.H., R.E., H.B., M.H.); Department of Plant and Environmental Sciences, Hebrew University of Jerusalem, Jerusalem 91904, Israel (S.K., J.L.-H., A.K.); Institute of Plant Physiology and Ecology, Shanghai Institutes for Biological Sciences, Chinese Academy of Science, Shanghai 200032, China (T.O.); and Universität Rostock, Institut für Chemie, D–18059 Rostock, Germany (W.R.)
The occurrence of a photorespiratory 2-phosphoglycolate metabolism in cyanobacteria is not clear. In the genome of the cyanobacterium Synechocystis sp. strain PCC 6803, we have identified open reading frames encoding enzymes homologous to those forming the plant-like C2 cycle and the bacterial-type glycerate pathway. To study the route and importance of 2-phosphoglycolate metabolism, the identified genes were systematically inactivated by mutagenesis. With a few exceptions, most of these genes could be inactivated without leading to a high-CO2-requiring phenotype. Biochemical characterization of recombinant proteins verified that Synechocystis harbors an active serine hydroxymethyltransferase, and, contrary to higher plants, expresses a glycolate dehydrogenase instead of an oxidase to convert glycolate to glyoxylate. The mutation of this enzymatic step, located prior to the branching of phosphoglycolate metabolism into the plant-like C2 cycle and the bacterial-like glycerate pathway, resulted in glycolate accumulation and a growth depression already at high CO2. Similar growth inhibitions were found for a single mutant in the plant-type C2 cycle and more pronounced for a double mutant affected in both the C2 cycle and the glycerate pathway after cultivation at low CO2. These results suggested that cyanobacteria metabolize phosphoglycolate by the cooperative action of the C2 cycle and the glycerate pathway. When exposed to low CO2, glycine decarboxylase knockout mutants accumulated far more glycine and lysine than wild-type cells or mutants with inactivated glycerate pathway. This finding and the growth data imply a dominant, although not exclusive, role of the C2 route in cyanobacterial phosphoglycolate metabolism.
1 The work was supported by a grant from the Deutsche Forschungsgemeinschaft and from the Landesgraduiertenförderungsprogramm Mecklenburg-Vorpommern. 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: Martin Hagemann (martin.hagemann{at}uni-rostock.de). www.plantphysiol.org/cgi/doi/10.1104/pp.106.082982 * Corresponding author; e-mail martin.hagemann{at}uni-rostock.de; fax 49(0)3814986112. Received May 2, 2006; accepted July 24, 2006. This article has been cited by other articles:
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