JXB Advance Access originally published online on March 2, 2008
Journal of Experimental Botany 2008 59(7):1799-1809; doi:10.1093/jxb/ern016
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RESEARCH PAPER |
Overproduction of C4 photosynthetic enzymes in transgenic rice plants: an approach to introduce the C4-like photosynthetic pathway into rice
1Photobiology and Photosynthesis Research Unit, National Institute of Agrobiological Sciences (NIAS), Kannondai, Tsukuba 305-8602, Japan
2University Farm, Graduate School of Agricultural and Life Sciences, The University of Tokyo, 1-1-1 Midoricho, Nishitokyo, Tokyo 188-0002, Japan
¶ To whom correspondence should be addressed. E-mail: mmiyao{at}affrc.go.jp
Four enzymes, namely, the maize C4-specific phosphoenolpyruvate carboxylase (PEPC), the maize C4-specific pyruvate, orthophosphate dikinase (PPDK), the sorghum NADP-malate dehydrogenase (MDH), and the rice C3-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 CO2 assimilation, while in the case of PEPC it was slightly reduced. The reduction in CO2 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 CO2 assimilation, however, was more marked at higher CO2 concentrations, an indication that overproduction of the four enzymes in combination did not act to concentrate CO2 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 C4-like photosynthetic pathway into C3 plants, are discussed.
Key words: C4 photosynthesis, malate dehydrogenase, malic enzyme, overproduction, phosphoenolpyruvate carboxylase, pyruvate, orthophosphate dikinase, transgenic rice
* Present address: Faculty of Agriculture and Life Science, Hirosaki University, Hirosaki 036-8561, Japan.
Present address: Chiben-Gakuen High School, Gojo, Nara 637-0042, Japan.
Present address: Plant Pathology Department, University of Nebraska-Lincoln, Lincoln, NE 68583-0722, USA.
Present address: Graduate School of Agriculture, Kobe University, Kobe 657-8501, Japan.
Received 15 October 2007; Revised 22 December 2007 Accepted 11 January 2008
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