RUI: Assessing C4-pathway regulation by the pyruvate phosphate dikinase regulatory protein in maize leaves

几乎所有的植物都通过一种古老的光合作用过程将二氧化碳转化为碳水化合物，这一过程被称为C3光合作用（即C3植物）。植物的一个子集利用更有效的光合作用过程，称为C4光合作用（即C4植物）。在开阔的阳光环境下，C4植物的CO2固定速率、生物量积累速率和籽粒产量几乎是C3植物的两倍。C4植物与C3植物相比光合作用性能的提高部分是由于一组额外的光合CO2固定酶的进化，即C4途径。尽管C4植物比C3植物天生具有更高的生产力，但在农艺学上只有四种重要的C4作物：玉米、高粱、甘蔗和柳枝草。所有其他作物物种（如水稻、大豆、小麦）都是C3植物。因此，植物科学家正在进行的研究目标是将C4光合作用培育或改造成C3作物，以提高产量。迄今为止的努力还不够，部分原因是缺乏对C4途径如何在叶片中被控制以优化利用可用阳光的理解。这个项目的最终目的是阐明这种监管是如何运作的。这项工作的第一步，也是这个为期一年的项目的目标，是培育缺乏两种相互关联的光响应C4途径酶——丙酮酸磷酸二激酶（PPDK）和PPDK调节蛋白（RP）的玉米植株。据推测，这些酶通过C4途径控制二氧化碳的固定速率，以响应阳光。利用RNA干扰，一种基因工程方法，将分离出具有较低水平PPDK或RP酶的玉米植株稳定系。随后将评估这些植物的光合作用性能。从这些分析中，PPDK和RP如何赋予阳光响应性C4通路调节的准确图景有望出现。这一知识对于目前正在进行的寻求将功能性C4途径引入C3作物物种叶片的项目至关重要。该项目的主要教育和培训部分是生物化学/生物技术本科学位学生参与完成他们的毕业论文研究要求。

Almost all plants fix CO2 into carbohydrate using an ancient photosynthetic process termed C3 photosynthesis (i.e., C3 plants). A subset of plants utilize a more efficient photosynthetic process termed C4 photosynthesis (i.e., C4 plants). In open sunny environments the rate of CO2 fixation, biomass accumulation, and grain yield in C4 plants is nearly twice that of C3 plants. The increased photosynthetic performance of C4 versus C3 plants is due in part to the evolution of an additional set of photosynthetic CO2 fixation enzymes referred to as the C4 pathway. Despite the inherently higher productivity of C4 versus C3 plants, there are only four agronomically important C4 crop species: maize, Sorghum, sugar cane, and switch grass. All other crop species (e.g., rice, soybean, wheat) are C3 plants. Thus an ongoing research goal of plant scientists is to breed or engineer C4 photosynthesis into C3 crop plants for improving yields. Efforts to date have fallen short in part because of the lack of understanding on how the C4 pathway is controlled in leaves for optimizing use of available sunlight. The ultimate aim of this project is to elucidate how such regulation works. A first step in this endeavor, and the goal of this one-year project, is to develop maize plants that are deficient in two interrelated light-responsive C4 pathway enzymes, pyruvate phosphate dikinase (PPDK) and the PPDK regulatory protein (RP). It is hypothesized that these enzymes control the rate of the CO2 fixation by the C4 pathway in response to sunlight. Using RNA interference, a genetic engineering method, stable lines of maize plants will be isolated with reduced levels of PPDK or RP enzyme. These plants will be subsequently assessed for photosynthetic performance. From these analyses, an accurate picture of how PPDK and RP confer sunlight-responsive C4 pathway regulation is expected to emerge. This knowledge will be critical for projects now underway that seek to introduce a functional C4 pathway into leaves of C3 crop species. A major education and training component of the project is the participation of undergraduate Biochemistry/Biotechnology degree students in fulfillment of their senior thesis research requirement.