title: Overproduction of C4 photosynthetic enzymes in transgenic rice plants: an approach to introduce the C4-like photosynthetic pathway into rice.
abstract: Four enzymes, namely, the maize C(4)-specific phosphoenolpyruvate carboxylase (PEPC), the maize C(4)-specific pyruvate, orthophosphate dikinase (PPDK), the sorghum NADP-malate dehydrogenase (MDH), and the rice C(3)-specific NADP-malic enzyme (ME), were overproduced in the mesophyll cells of rice plants independently or in combination. Overproduction individually of PPDK, MDH or ME did not affect the rate of photosynthetic CO(2) assimilation, while in the case of PEPC it was slightly reduced. The reduction in CO(2) assimilation in PEPC overproduction lines remained unaffected by overproduction of PPDK, ME or a combination of both, however it was significantly restored by the combined overproduction of PPDK, ME, and MDH to reach levels comparable to or slightly higher than that of non-transgenic rice. The extent of the restoration of CO(2) assimilation, however, was more marked at higher CO(2) concentrations, an indication that overproduction of the four enzymes in combination did not act to concentrate CO(2) inside the chloroplast. Transgenic rice plants overproducing the four enzymes showed slight stunting. Comparison of transformants overproducing different combinations of enzymes indicated that overproduction of PEPC together with ME was responsible for stunting, and that overproduction of MDH had some mitigating effects. Possible mechanisms underlying these phenotypic effects, as well as possibilities and limitations of introducing the C(4)-like photosynthetic pathway into C(3) plants, are discussed.
authors.affiliation: Photobiology and Photosynthesis Research Unit, National Institute of Agrobiological Sciences (NIAS), Kannondai, Tsukuba 305-8602, Japan.
authors.forename: Yojiro
authors.initials: Y
authors.lastname: Taniguchi
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Ohkawa
authors.forename: Chisato
authors.initials: C
authors.lastname: Masumoto
authors.forename: Takuya
authors.initials: T
authors.lastname: Fukuda
authors.forename: Tesshu
authors.initials: T
authors.lastname: Tamai
authors.forename: Kwanghong
authors.initials: K
authors.lastname: Lee
authors.forename: Sizue
authors.initials: S
authors.lastname: Sudoh
authors.forename: Hiroko
authors.initials: H
authors.lastname: Tsuchida
authors.forename: Haruto
authors.initials: H
authors.lastname: Sasaki
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Fukayama
authors.forename: Mitsue
authors.initials: M
authors.lastname: Miyao
mesh_terms: D018506:Gene Expression Regulation, Plant / Q000235:genetics / Q000502:physiology; D005818:Genetic Engineering; D008291:Malate Dehydrogenase / Q000235:genetics / Q000378:metabolism; D050538:Malate Dehydrogenase (NADP+) / Q000235:genetics / Q000378:metabolism; D012275:Oryza / Q000201:enzymology* / Q000235:genetics*; D019764:Phosphoenolpyruvate Carboxykinase (ATP) / Q000235:genetics / Q000378:metabolism; D010788:Photosynthesis / Q000502:physiology*; D018515:Plant Leaves / Q000378:metabolism; D030821:Plants, Genetically Modified; D011772:Pyruvate, Orthophosphate Dikinase / Q000235:genetics / Q000378:metabolism
chemical_list: D008291:Malate Dehydrogenase; C031917:malate dehydrogenase (oxaloacetate-decarboxylating) (NADP+); D050538:Malate Dehydrogenase (NADP+); D011772:Pyruvate, Orthophosphate Dikinase; D019764:Phosphoenolpyruvate Carboxykinase (ATP)