Overproduction of C4 photosynthetic enzymes in transgenic rice plants: an approach to introduce the C4-like photosynthetic pathway into rice.
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.
Taniguchi
Yojiro
Y
Photobiology and Photosynthesis Research Unit, National Institute of Agrobiological Sciences (NIAS), Kannondai, Tsukuba 305-8602, Japan.
Ohkawa
Hiroshi
H
Masumoto
Chisato
C
Fukuda
Takuya
T
Tamai
Tesshu
T
Lee
Kwanghong
K
Sudoh
Sizue
S
Tsuchida
Hiroko
H
Sasaki
Haruto
H
Fukayama
Hiroshi
H
Miyao
Mitsue
M
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
D008291:Malate Dehydrogenase; C031917:malate dehydrogenase (oxaloacetate-decarboxylating) (NADP+); D050538:Malate Dehydrogenase (NADP+); D011772:Pyruvate, Orthophosphate Dikinase; D019764:Phosphoenolpyruvate Carboxykinase (ATP)