Tsuchida H, Tamai T, Fukayama H, Agarie S, Nomura M, Onodera H, Ono K, Nishizawa Y, Lee B H, Hirose S, Toki S, Ku M S, Matsuoka M, Miyao M
National Institute of Agrobiological Resources, Tsukuba, 305-8602 Japan.
Plant Cell Physiol. 2001 Feb;42(2):138-45. doi: 10.1093/pcp/pce013.
The chloroplastic NADP-malic enzyme (NADP-ME) is a key enzyme of the C4 photosynthesis pathway in NADP-ME type C4 plants such as maize. To express the chloroplastic NADP-ME in leaves of a C3 plant, rice, full-length cDNAs encoding the rice C3-specific isoform and the maize C4-specific isoform of the enzyme were expressed under the control of the rice CAB: promoter. Transformants carrying the rice cDNA showed the NADP-ME activities in the leaves less than several-fold that of non-transformants, while those carrying the maize cDNA showed activities up to 30-fold that of non-transformants or about 60% of the NADP-ME activity of maize leaves. These results indicate that expression of the rice C3-specific NADP-ME is suppressed at co- and/or post-transcriptional levels by some regulation mechanisms intrinsic to rice, while that of the foreign C4-specific isoform can escape from such suppression. The accumulation of the maize C4-specific NADP-ME led to bleaching of leaf color and growth hindrance in rice plants under natural light. These deteriorative effects resulted from enhanced photoinhibition of photosynthesis due to an increase in the level of NADPH inside the chloroplast by the action of the maize enzyme.
叶绿体NADP - 苹果酸酶（NADP - ME）是玉米等NADP - ME型C4植物中C4光合作用途径的关键酶。为了在C3植物水稻的叶片中表达叶绿体NADP - ME，编码该酶水稻C3特异性同工型和玉米C4特异性同工型的全长cDNA在水稻CAB启动子的控制下进行表达。携带水稻cDNA的转化体叶片中的NADP - ME活性比未转化体高不到几倍，而携带玉米cDNA的转化体的活性比未转化体高30倍，或约为玉米叶片NADP - ME活性的60%。这些结果表明，水稻C3特异性NADP - ME的表达在转录和/或转录后水平受到水稻固有某些调控机制的抑制，而外源C4特异性同工型的表达可以逃避这种抑制。在自然光下，玉米C4特异性NADP - ME的积累导致水稻植株叶片颜色变白和生长受阻。这些不良影响是由于玉米酶的作用使叶绿体内部NADPH水平升高，从而增强了光合作用的光抑制作用所致。
