Adaptation of C4 Photosynthesis to Cold within the Miscanthus Genus

芒属植物C4光合作用对寒冷的适应并不是所有的植物在将太阳能转化为生物量并最终为人类提供食物的效率上都是一样的。目前已知的效率最高的植物是C4植物，它们利用二氧化碳（CO2）和太阳光产生四种碳化合物，作为光合作用的初始产物。世界上大多数植物都是C3植物，在理想条件下生长时，它们利用阳光的效率比C4植物低40%左右。C4植物，如热带草和作物品种玉米、高粱和甘蔗仍然主要局限于温暖的温带环境。这些观察结果表明，C4光合作用的更高效率本质上仅限于温暖的条件。最近的研究表明，一些芒草物种不仅能在寒冷的气候中生存，而且它们的光合速率和将光转化为生物量的效率也超过了C3物种。然而，这些物种完全是C4，与热带甘蔗密切相关，它们可以形成肥沃的杂交品种。从甘蔗多样性的中心，被分类为芒草的形式已经辐射到东南亚的高海拔寒冷草原生境；在C4机制中形成了一个可能的耐寒性进程。在密切相关的分类群中，这种非常大的耐寒性范围为发现C4光合作用的耐寒性是如何进化的提供了一个独特的机会。从热带到寒温带，这种芒草-糖蜜复合体的分类群具有在低温下发育具有光合能力的叶片和在低温下进行光合作用的能力。这项研究将为测试一系列相互竞争的理论提供基础，但不一定是唯一的理论，这些理论通常限制了C4在低温下的光合作用。理论包括：Rubisco酶在低温下的催化能力过低，丙酮酸正磷酸二激酶（PPDK）酶在低温下不稳定，对过度光抑制光合作用的保护能力不足。这些将通过体内和体外活性和数量的测量来评估，使用经典的生理和生物化学技术，并在分子水平上研究基因序列变化和蛋白质稳定性，包括与伴侣蛋白的关联。回归分析将用于评估这些特征中哪一个解释了该复合体的分类群中低温耐受性的最大变化。这项工作还将对教育活动和农业产生更广泛的影响。对C4光合作用适应寒冷条件的生理和分子机制的进一步了解，可能为延长C4作物（如玉米、高粱和甘蔗）的生长季节或种植环境提供新的策略。该项目还将强调对高中、本科和研究生的研究培训，包括为少数民族学生提供实习机会，将植物生物学和作物生产的新方法结合起来。此外，研究结果将通过强调环境变化及其对农业影响的实地考察和教育介绍向广大公众宣传。

Adaptation of C4 Photosynthesis to Cold within the Miscanthus GenusNot all plants are equal in the efficiency with which they convert sunlight energy into biomass and ultimately provide food for people. The most efficient plants known are C4 plants, which use carbon dioxide (CO2) and sunlight energy to make four carbon compounds as the initial product of photosynthesis. The majority of the world's plants are C3 plants, which when grown under ideal conditions are about 40% less efficient in their use of sunlight than C4 plants. C4 plants such as tropical grasses and the crop species corn, sorghum and sugarcane remain largely confined to warm temperate environments. These observations have led to the suggestion that the higher efficiency of C4 photosynthesis was inherently limited to warm conditions. Recent work has shown that some Miscanthus species not only survive in cold climates, but that they achieve photosynthetic rates and efficiencies of conversion of light into biomass that exceed those of C3 species. Yet these species are exclusively C4 and are so closely related to tropical sugarcane that they can form fertile hybrids. From the center of diversity of sugarcane, forms classified as Miscanthus have radiated out into high-altitude cold grassland habitats in S.E. Asia; forming a likely progression of cold tolerance within the C4 mechanism. This very large range of cold tolerance within closely related taxa provides a unique opportunity to discover how cold tolerance has evolved within C4 photosynthesis. Taxa from this Miscanthus-Saccharum complex occurring in a range of habitats from tropical to cold temperate, will be characterized for their ability to develop photosynthetically competent leaves at low temperature and to photosynthesize at low temperature. This research will provide a basis for testing a range of competing, but not necessarily exclusive, theories on what normally limits C4 photosynthesis at low temperature. Theories include: that the catalytic capacity of the enzyme Rubisco at low temperature is too low, that the enzyme pyruvate orthophosphate dikinase (PPDK) is unstable at low temperature, and that there is inadequate capacity for protection against inhibition of photosynthesis by excess light. These will be assessed by in vivo and in vitro measurement of activity and quantities, using classical physiological and biochemistry techniques, and at the molecular level investigating gene sequence changes and protein stability, including association with chaperone proteins. Regression analysis will be used to assess which of these characters explains most variation in low temperature tolerance across the taxa of this complex. This work will also have broader impacts to both educational activities and agriculture. An improved understanding of the physiological and molecular mechanisms associated with the adaptation of C4 photosynthesis to cold conditions may offer novel strategies to extending the growing season or cultivation environments of C4 crops such as corn, sorghum and sugarcane. This project will also emphasize research training for students from the high school, undergraduate and graduate levels, including internship opportunities for minority students that integrate plant biology and new approaches to crop production. Furthermore, research results will be communicated to the public at large through field tours and educational presentations that emphasize environmental change and its impacts to agriculture.