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首页> 外文会议>Gamma Field Symposia no.43; Symposium on Improvement of Crop Productivity and Mutation; 20040714-15; Ibaraki-ken(JP) >OVERPRODUCTION OF C_4 PHOTOSYNTHETIC ENZYMES IN TRANSGENIC RICE: A BIOTECHNOLOGICAL APPROACH TO ALTER C_3 PHOTOSYNTHESIS
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OVERPRODUCTION OF C_4 PHOTOSYNTHETIC ENZYMES IN TRANSGENIC RICE: A BIOTECHNOLOGICAL APPROACH TO ALTER C_3 PHOTOSYNTHESIS

机译：转基因水稻中C_4光合酶的过量生产：改变C_3光合作用的生物技术方法

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摘要

Most terrestrial plants, including many important crops, such as rice, wheat, soybean, and potato, assimilate CO_2 through the C_3 photosynthetic pathway and are classified as C_3 plants. However, some plants, such as maize and sugarcane, possess the C_4 photosynthetic pathway in addition to the C_3 pathway (Fig. 1), and these are classified as C_4 plants. C_4 plants are assumed to evolve from C_3 plants in response to changes in atmospheric conditions, especially a drastic decline of CO_2 level (EHLERINGER and MONSON 1993). The C_4 pathway acts to concentrate CO_2 at the site of the reactions of the C_3 pathway, and thus inhibits photorespiration (HATCH 1987; Fig. 1B). This CO_2-concentrating mechanism, together with modifications of leaf anatomy, enables C_4 plants to achieve high photosynthetic capacity and high water and nitrogen use efficiencies (HATCH 1987). Consequently, the transfer of C_4 traits to C_3 plants is one strategy being adopted for improving the photosynthetic performance of C_3 plants. The C_4 pathway consists of three key steps: (ⅰ) the initial fixation of CO_2 in the mesophyll-cell cytosol by phosphoenolpyruvate carboxylase (PEPC) to form a C_4 acid, (ⅱ) decarboxylation of a C_4 acid in the bundle sheath cells to release CO_2, and (ⅲ) regeneration of the primary CO_2 acceptor phosphoenolpyruvate (PEP) in the mesophyll-cell chloroplasts by pyruvate, orthophosphate dikinase (PPDK) (HATCH 1987). The decarboxylation reaction is catalyzed by one or more of the three enzymes, namely, NADP-malic enzyme (NADP-ME), NAD-malic enzyme, and phosphoenolpyruvate carboxykinase (PEP-CK), and C4 plants are classified into three subtypes depending on the major decarboxylation enzyme. Maize and sugarcane use NADP-ME and are classified as the NADP-ME type (HATCH 1987). To drive the C_4 pathway in the mesophyll cell of C_3 plants, at least three key C_4 photosynthetic enzymes, namely, PEPC, PPDK, and NADP-ME, will need to be expressed at high levels (Fig. 2). Previously, attempts have been made to transfer C_4 traits to C_3 plants by conventional hybridization between C_3 and C_4 plants (BROWN and BOUTON 1993). However, this approach was available only in several plant genera, and moreover, most C_3-C_4 hybrids showed infertility due to abnormal chromosome pairing and/or genetic barriers. Recent developments in plant genetic engineering have enabled us to express the desired genes encoding C_4 enzymes at high levels and in desired locations in the leaves of C_3 plants.
机译：大多数陆生植物，包括许多重要农作物，例如水稻，小麦，大豆和马铃薯，都通过C_3光合作用途径吸收CO_2，并被分类为C_3植物。但是，一些植物，例如玉米和甘蔗，除了具有C_3途径外，还具有C_4光合作用途径（图1），这些植物被归类为C_4植物。假定C_4植物是从C_3植物演变而来的，以响应大气条件的变化，尤其是CO_2水平的急剧下降（EHLERINGER和MONSON 1993）。 C_4通路的作用是将CO_2集中在C_3通路的反应部位，从而抑制光呼吸作用（HATCH 1987；图1B）。这种CO_2浓缩机制，加上对叶片解剖结构的修改，使C_4植物具有较高的光合作用能力以及较高的水和氮利用效率（HATCH 1987）。因此，将C_4性状转移至C_3植物是提高C_3植物光合性能的一种策略。 C_4途径包括三个关键步骤：（ⅰ）磷酸烯醇丙酮酸羧化酶（PEPC）将CO_2初步固定在叶肉细胞质中，形成C_4酸，（ⅱ）束鞘细胞中C_4酸脱羧以释放CO_2，以及（×）丙酮酸，正磷酸二激酶（PPDK）在叶肉细胞叶绿体中再生主要CO_2受体磷酸烯醇丙酮酸（PEP）（HATCH 1987）。脱羧反应由三种酶中的一种或多种催化，即NADP-苹果酸酶（NADP-ME），NAD-苹果酸酶和磷酸烯醇丙酮酸羧激酶（PEP-CK），并且C4植物根据其分为三类主要的脱羧酶。玉米和甘蔗使用NADP-ME类型，被归类为NADP-ME类型（HATCH 1987）。为了在C_3植物的叶肉细胞中驱动C_4途径，至少需要高表达3种关键的C_4光合酶，即PEPC，PPDK和NADP-ME（图2）。以前，已经尝试通过C_3和C_4植物之间的常规杂交将C_4性状转移到C_3植物中（BROWN和BOUTON 1993）。但是，这种方法仅在几个植物属中可用，而且，大多数C_3-C_4杂种由于异常的染色体配对和/或遗传障碍而表现出不育性。植物基因工程的最新发展使我们能够在C_3植物叶片的高水平和所需位置表达编码C_4酶的所需基因。

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