title: Overexpression of C(4)-cycle enzymes in transgenic C(3) plants: a biotechnological approach to improve C(3)-photosynthesis.
abstract: The process of photorespiration diminishes the efficiency of CO(2) assimilation and yield of C(3)-crops such as wheat, rice, soybean or potato, which are important for feeding the growing world population. Photorespiration starts with the competitive inhibition of CO(2) fixation by O(2) at the active site of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) and can result in a loss of up to 50% of the CO(2) fixed in ambient air. By contrast, C(4) plants, such as maize, sugar cane and Sorghum, possess a CO(2) concentrating mechanism, by which atmospheric CO(2) is bound to C(4)-carbon compounds and shuttled from the mesophyll cells where the prefixation of bicarbonate occurs via phosphoenolpyruvate carboxylase (PEPC) into the gas-tight bundle-sheath cells, where the bound carbon is released again as CO(2) and enters the Calvin cycle. However, the anatomical division into mesophyll and bundle-sheaths cells ("Kranz"-anatomy) appears not to be a prerequisite for the operation of a CO(2) concentrating mechanism. Submerged aquatic macrophytes, for instance, can induce a C(4)-like CO(2) concentrating mechanism in only one cell type when CO(2) becomes limiting. A single cell C(4)-mechanism has also been reported recently for a terrestrial chenopod. For over 10 years researchers in laboratories around the world have attempted to improve photosynthesis and crop yield by introducing a single cell C(4)-cycle in C(3) plants by a transgenic approach. In the meantime, there has been substantial progress in overexpressing the key enzymes of the C(4) cycle in rice, potato, and tobacco. In this review there will be a focus on biochemical and physiological consequences of the overexpression of C(4)-cycle genes in C(3) plants. Bearing in mind that C(4)-cycle enzymes are also present in C(3) plants, the pitfalls encountered when C(3) metabolism is perturbed by the overexpression of individual C(4) genes will also be discussed.
authors.affiliation: Botanik II, Botanisches Institut der Universität zu Köln, Gyrhofstrasse 15, D-50931 Cologne, Germany. rainer.haeusler@uni-koeln.de
authors.forename: Rainer E
authors.initials: RE
authors.lastname: Häusler
authors.forename: Heinz-Josef
authors.initials: HJ
authors.lastname: Hirsch
authors.forename: Fritz
authors.initials: F
authors.lastname: Kreuzaler
authors.forename: Christoph
authors.initials: C
authors.lastname: Peterhänsel
mesh_terms: D002245:Carbon Dioxide / Q000378:metabolism; D002256:Carbonic Anhydrases / Q000378:metabolism; D004798:Enzymes / Q000235:genetics* / Q000378:metabolism; D015971:Gene Expression Regulation, Enzymologic; D018506:Gene Expression Regulation, Plant; D008291:Malate Dehydrogenase / Q000235:genetics / Q000378:metabolism; D010100:Oxygen / Q000378:metabolism; D010730:Phosphoenolpyruvate Carboxylase / Q000235:genetics / Q000378:metabolism; D010788:Photosynthesis / Q000235:genetics* / Q000502:physiology; D045322:Photosynthetic Reaction Center Complex Proteins / Q000235:genetics / Q000378:metabolism; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D010944:Plants / Q000145:classification / Q000235:genetics* / Q000378:metabolism; D030821:Plants, Genetically Modified; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism; D011772:Pyruvate, Orthophosphate Dikinase; D012273:Ribulose-Bisphosphate Carboxylase / Q000235:genetics / Q000378:metabolism
chemical_list: D004798:Enzymes; D045322:Photosynthetic Reaction Center Complex Proteins; D010940:Plant Proteins; D002245:Carbon Dioxide; D008291:Malate Dehydrogenase; C046446:malate dehydrogenase-(oxaloacetate-decarboxylating) (NAD+); C031917:malate dehydrogenase (oxaloacetate-decarboxylating) (NADP+); C069767:phosphoenolpyruvate carboxylase kinase; D017346:Protein Serine-Threonine Kinases; C037396:PPDK protein, Zea mays; D011772:Pyruvate, Orthophosphate Dikinase; D010730:Phosphoenolpyruvate Carboxylase; D012273:Ribulose-Bisphosphate Carboxylase; D002256:Carbonic Anhydrases; D010100:Oxygen