Dimensions: Collaborative Proposal: Molecular, ecological and evolutionary dynamics of carbon fixation and diversification in Agavoideae (Asparagaceae) and Oncidiinae (Orchidaceae)

光合作用是维持地球上绝大多数生命的基本过程。然而，对于生活在缺水条件下的植物来说，更热和更干燥的气候条件可能会降低光合作用生产率。为了抵消这些条件，一些植物利用光合作用的形式来提高它们利用水分的效率。在沙漠或其他水分有限的栖息地生长的植物中看到的一种这样的创新被称为CAM(景天酸代谢)。CAM创新在大量不同的植物谱系中发现，通常与茎(如仙人掌)或叶(如龙舌兰)肉质有关。拟议的研究项目将使用几种方法来解决基本问题，如植物如何利用CAM，以及参与执行CAM的基因如何调节以应对不同的环境条件。为了实现这一目标，该项目将专注于兰花和龙舌兰植物家族中CAM的独立进化，这两个家族都有以在缺水环境中茁壮成长而闻名的物种。这项研究将为理解CAM途径的遗传基础提供基础，并有可能转移到经济上重要的植物，以提高干旱条件下的水分利用效率，从而提高生产力。此外，该项目将对本科生和研究生进行培训，包括来自任职人数不足群体的个人。还计划将项目成果纳入课堂学习和更广泛的外联活动。该项目利用一个关于两个CAM光合作用实例的综合研究计划来阐明将进化过程的生态、遗传和分子维度联系起来的机制，这些进化过程有助于生物多样性的起源和维持。光合作用是支持地球上绝大多数生态群落生物多样性的基本过程，同时也是生活在缺水条件下的初级生产者面临的生理挑战。光合作用生物的进化史包括在极端环境条件下提高水分利用效率和生产力的碳浓缩机制的反复起源。景天酸代谢就是这样一种创新，它促进了一系列生境中维管植物谱系的多样化。拟议的项目将整合生态学、生理学、系统发育、遗传学和基因组学方法，以解决植物如何利用CAM以及参与执行CAM的基因如何因应不同的环境条件而受到调控的基本问题。本项目的研究系统是物种丰富的天冬科和文心兰科的谱系，这两个谱系都包括CAM、C3(典型的光合作用形式)和兼性或弱的CAM种。这些系统将有助于推断两个谱系中CAM光合作用的多重得失的系统发育和环境背景。对RNA的比较分析将阐明C3和CAM光合作用转变的相互作用的分子和环境驱动因素，以及这些转变对物种多样性起源和维持的影响。此外，与CAM得失相关的基因功能变化将通过对丝兰杂交的遗传分析来测试，该杂交是由CAM和C3亲本物种的自然杂交产生的，以及对新兴兰花模式物种Erycina pusilla(Oncidiinae)的基因表达的实验操作。

Photosynthesis is a basic process supporting the vast majority of life on Earth. However, for plants living under water-limited conditions, photosynthetic productivity can be reduced by hotter and drier climatic conditions. To counteract these conditions, some plants utilize forms of photosynthesis that increase the efficiency with which they use water. One such innovation seen in plants that grow in deserts or other water-limited habitats is referred to as CAM (Crassulacean Acid Metabolism). The CAM innovation is found in a large number of diverse plant lineages and typically associated with stem (e.g. cacti) or leaf (e.g. agaves) succulence. The proposed research project will use several approaches to address fundamental questions about how plants use CAM and how genes involved in performing CAM are regulated in response to varying environmental conditions. To achieve this, the project will focus on the independent evolution of CAM in the orchid and agave plant families, both of which have species known for their ability to thrive in water-limited environments. This research will provide a foundation for understanding the genetic basis of CAM pathways and potentially transfer to economically important plants for improved water use efficiency under drought conditions leading to improved productivity. Additionally, this project would result in the training of undergraduate and graduate students, including individuals from under-represented groups. There are also plans to integrate the results of the project into classroom learning and broader outreach activities. This project utilizes an integrated research program on two instances of CAM photosynthesis to illuminate the mechanisms that link ecological, genetic and molecular dimensions of the evolutionary processes that contribute to the origin and maintenance of biodiversity. Photosynthesis is a fundamental process supporting biodiversity in the vast majority of ecological communities on our planet, while at the same time a physiological challenge for primary producers living under water-limited conditions. The evolutionary history of photosynthetic organisms has included repeated origins of carbon concentrating mechanisms that increase water-use efficiency and productivity in extreme environmental conditions. Crassulacean acid metabolism is one such innovation that has facilitated diversification of vascular plant lineages in an array of habitats. The proposed project will integrate ecological, physiological, phylogenetic, genetic and genomic approaches to address fundamental questions about how plants use CAM and how genes involved in performing CAM are regulated in response to different environmental conditions. The study systems for this project are the species-rich Agavoideae (Asparagaceae) and Oncidiinae (Orchidaceae) lineages, both of which include CAM, C3 (typical form of photosynthesis) and facultative or weak CAM species. These systems will aid in inferring the phylogenetic and environmental context for multiple gains and losses of CAM photosynthesis in both lineages. Comparative analyses of RNA will illuminate the interacting molecular and environmental drivers of shifts between C3 and CAM photosynthesis and the impact of these shifts on the origin and maintenance of species diversity. Furthermore, shifts in gene function associated with the gain and loss of CAM will be tested through genetic analyses of a yucca hybrid, resulting from a natural cross between a CAM and C3 parental species, and experimental manipulations of gene expression in the emerging orchid model species, Erycina pusilla (Oncidiinae).