Rubisco evolution, photosynthesis and plant adaptation to climate change

地球大气中二氧化碳浓度的增加正在推动全球变暖过程，这将对植物光合作用产生深远影响。一些关于未来气候变化的模型预测了21世纪后半叶令人担忧的情景，例如生物群崩溃和大范围的农作物歉收。为了更好地应对这些问题，我们必须了解植物光合作用对不同CO2浓度和温度的适应机制。不同的植物物种居住在地球上非常不同的气候区域。许多植物在它们的自然栖息地经历了很大的季节温度变化。他们还必须适应二氧化碳浓度和温度的变化，这些变化自开花植物进化以来发生了很大变化。在本项目中，我们将研究关键的光合酶核酮糖-1，5-二磷酸羧基加氧酶(Rubisco)的季节驯化和进化变化的机制。这种酶参与将无机碳(CO2)转化为有机化合物，最终是地球上几乎所有生物的有机物质来源。然而，该酶的性能是植物光合作用的瓶颈，它限制了作物和自然生态系统的生产力。在较高的温度下，Rubisco的工作效率往往较低，尽管该酶的最适温度取决于特定植物物种是否适应高温条件。这种酶对温度的依赖性以及它对温度变化的适应机制仍然不清楚，也存在争议。以前，我们证明了Rubisco的主要组成部分，即由单拷贝叶绿体基因(RbcL)编码的大亚基，在大多数陆生植物群体中是在强正向选择下进化的。在这种保守的酶中，正选择的普遍存在是相当令人惊讶的，可能反映了Rubisco在数百万年的植物进化过程中对不断变化的二氧化碳浓度和温度的适应。然而，这种选择性压力的原因(S)仍然不清楚，因为不同植物组中Rubisco酶的实际动力学参数。在这个项目中，我们将分析Rubisco生化特性的差异是否与来自不同气候的植物在特定氨基酸位置的正选择有关。我们还将测试在不同条件下生长的植物是否通过表达编码Rubisco小亚基(RBCs)和Rubisco激活酶(一种维持Rubisco处于活性配置的酶)的多基因家族的不同副本来调节该酶的性质。该项目的创新之处在于将基于系统发育的进化遗传分析在蛋白质水平上的选择与酶的生化特性分析相结合。这将使我们能够准确地定位编码Rubisco复合体的基因的具体变化，这些基因参与了对物种生态重大转变的适应。它还应该为世界上最丰富的酶在分子水平上因环境的具体变化而引起的适应提供一个重要的例子。了解植物在不同气候和不同条件下适应光合作用的方式，将有助于微调植物在不同条件下的光合作用表现，这在全球气候变化的背景下将是一个特别重要的挑战。

Increasing CO2 concentrations in the Earth's atmosphere are driving a process of global warming that will have a profound effect on plant photosynthesis. Some models of future climate change predict alarming scenarios for the latter part of the 21st century, such as biome collapses and widespread crop failures. To be better prepared to deal with such problems, we have to understand the mechanisms of adaptation of plant photosynthesis to varying CO2 concentrations and temperature. Different plant species inhabit very different climatic regions on Earth. Many plants experience large seasonal variations in temperature in their natural habitats. They also had to adapt to changes in CO2 concentration and temperature that have changed considerably since the evolution of flowering plants. In this project, we will study the mechanisms of both seasonal acclimation and evolutionary changes in the key photosynthetic enzyme ribulose-1,5-bisphospate carboxylase-oxygenase (Rubisco). This enzyme is involved in conversion of inorganic carbon (CO2) into organic compounds, and is ultimately the source of organic matter for almost all organisms on Earth. However, the performance of this enzyme is a bottleneck in plant photosynthesis and it limits the productivity of crops and natural ecosystems. At higher temperatures, Rubisco tends to work less efficiently, though the temperature optimum of the enzyme depends on whether the particular plant species is adapted to high temperature conditions. The mechanisms responsible for the temperature dependence of this enzyme its adaptation to temperature changes remain unclear and controversial. Previously, we demonstrated that the main component of Rubisco, the large subunit, which is encoded by a single-copy chloroplast gene ( rbcL), evolved under strong positive selection in most groups of terrestrial plants. The ubiquity of positive selection in this conservative enzyme is quite surprising and may reflect adaptation of Rubisco to changing CO2 concentration and temperatures over millions of years of plant evolution. However, the cause of this selective pressure(s) remains unclear because the actual kinetic parameters of Rubisco enzyme in different plant groups. In this project, we will analyse whether differences in the biochemical properties of Rubisco are associated with positive selection at specific amino acid positions in plants from different climates. We will also test whether the plants grown under different conditions adjust the properties of this enzyme by expressing different copies of multigene families encoding the small subunit of Rubisco (rbcS) and Rubisco activase, an enzyme that maintains Rubisco in an active configuration. The novelty in this project lies in the combination of phylogeny-based evolutionary genetic analysis of selection at the protein level with analysis of enzyme biochemical properties. This will allow us to pinpoint specific changes in genes encoding the Rubisco complex that have been involved in adaptation to major shifts in species ecology. It should also provide an important example of adaptation at the molecular level caused by specific changes in the environment for the most abundant enzyme in the world. Understanding the ways in which plants have adapted their photosynthetic optimum in different climates and under different conditions will help to fine-tune plant photosynthetic performance in different conditions, which will be a particularly important challenge in the context of global climate change.