Mechanisms of C4 Photosynthetic Evolution

C4光合作用通过抑制光呼吸的浪费过程来提高高等植物的生产力和资源利用效率。 尽管有其优点，但很少有主要的粮食和纤维作物使用C4途径，而是依赖于C3途径，这可能会遭受高速率的光呼吸。为了满足对食物、纤维和燃料日益增长的需求，人们对进一步利用C4光合作用非常感兴趣，无论是通过将C4途径工程化到C3作物中，改进现有的C4作物，还是驯化野生C4物种。多伦多大学的Sage实验室是C4植物生物学领域公认的领导者，在分子机制、基因组学、整株植物生理学、光合进化、系统学和生态学/生物多样性之间的接口方面拥有专业知识。 通过我们的努力，我们已经证明C4光合作用至少进化了65次，这表明它在自然界中相对容易进化，人类可以将其改造成我们的C3作物，如小麦和水稻。 通过研究C4植物如何进化，我们应该能够了解如何将C4途径工程化到C3植物中，并改进现有的C4作物。 在这项提案中，要求提供资金，以支持将阐明C4光合作用进化的生理，发育和分子机制的研究。为了支持这项工作，我们从34个独立的C4光合作用起源中获得了世界上最大的相关C3，C4和C3-C4中间物种，包括来自9个C4进化谱系的C3-C4中间物种。 这种多样性将使我们能够使用比较的方法来研究C4光合作用进化的生理，发育和分子机制。在比较研究中，我们将描述C4性状的收购沿着一个进化梯度的属，如Blepharis和Flaveria，其中包含多个物种的中间C3- C4性状。然后将性状获得与物种的转录组进行比较，以确定基因表达的相应变化。我们还产生了C3和C4种滨藜的可育杂种，其表现出C4性状的分离。 利用杂交种转录组中亲本基因分类的组合分析，沿着叶生理学、细胞生物学和发育的测量，我们将能够将遗传控制与特定C4性状的表达联系起来。总之，比较方法和混合分析将为我们提供前所未有的能力，发现C4性状表达的关键控制，并解决在进化过程中，他们从事。通过我们的工作，新的候选基因将被输送到C4水稻项目中，为该项目的成功做出贡献，该项目可以将水稻和小麦等主要作物的效率提高50%或更多，从而在可预见的未来消除世界饥饿。

C4 photosynthesis enhances productivity and resource-use efficiency in higher plants by inhibiting the wasteful process of photorespiration. Despite its advantages, few major food and fiber crops use the C4 pathway, relying instead on the C3 pathway which can suffer from high rates of photorespiration. To meet growing demands for food, fiber and fuel, there is much interest in further exploiting C4 photosynthesis, either through the engineering of the C4 pathway into C3 crops, improving existing C4 crops, or domesticating wild C4 species. The Sage lab at the University of Toronto is a recognized leader in C4 plant biology, with expertise at the interfaces between molecular mechanisms, genomics, whole plant physiology, photosynthetic evolution, systematics, and ecology/biodiversity. Through our efforts, we have shown that C4 photosynthesis evolved at least 65 times, indicating it is relatively easy to evolve in nature and for humanity to engineer into our C3 crops, such as wheat and rice. By studying how C4 plants evolved, we should be able to learn how to engineer the C4 pathway into C3 plants, and to improve existing C4 crops. In this proposal, funds are requested to support research that will elucidate the physiological, developmental, and molecular mechanisms governing the evolution of C4 photosynthesis. To support this work, we have acquired the world's largest collection of related C3, C4 and C3-C4 intermediate species from 34 independent origins of C4 photosynthesis, including a diverse set of C3-C4 intermediate species from nine C4 evolutionary lineages. This diversity will enable us to use a comparative approach to examine the physiological, developmental and molecular mechanisms by which C4 photosynthesis evolved. In the comparative studies, we will characterize C4 trait acquisition along an evolutionary gradient in genera such as Blepharis and Flaveria, which contain multiple species with intermediate C3- C4 traits. Trait acquisition will then be compared with the species' transcriptomes to identify corresponding shifts in gene expression. We have also generated fertile hybrids of C3 and C4 species of Atriplex which exhibit segregation of C4 traits. Using a combined analysis of parental gene assortment in the transcriptomes of the hybrids, along with measurement of leaf physiology, cell biology and development, we will be able to link genetic controls with the expression of specific C4 traits. Together, the comparative approach and the hybrid analysis will provide us with an unprecedented ability to discover critical controls over C4 trait expression, and to address when during the evolutionary process they were engaged. Through our work, novel gene candidates will be funneled to the C4 Rice effort, contributing to the success of a program that could improve the efficiency of major crops such as rice and wheat by 50% or more, thus eliminating world hunger for the foreseeable future.