Components of the CO2-Concentrating System

与C3植物相比，莱茵衣藻和其他单细胞藻类表现出不同寻常的光合特性。有人提出，这些特征是由于CO2浓缩系统的运行，该系统通过竞争性抑制RuBP加氧酶，将细胞内CO2浓度增加到抑制光呼吸的水平。该系统的主要成分之一是一种蛋白质，它催化无机碳在质膜或叶绿体包膜上的主动运输。然而，这种转运体或除碳酸酐酶以外的任何其他二氧化碳浓缩系统组分存在的直接物理证据是缺乏的。二氧化碳浓缩系统的活动受环境控制。在限制CO2浓度下生长的细胞（适应空气）显示出活性，但在高CO2浓度下生长的细胞（CO2富集）显示出CO2浓缩系统没有活性。我们已经确定了7种多肽，它们在适应限制二氧化碳浓度的过程中丰度增加，或者是在这种条件下生长的细胞所特有的。我们将继续将这些观察结果扩展到比较野生型和突变型衣藻缺乏二氧化碳浓缩系统，以帮助确定哪些多肽可能直接参与无机碳积累。使用针对一种或多种“空气特异性”多肽产生的抗体，我们期望：(1)确定co2浓缩系统“诱导”过程中“空气特异性”多肽的出现是否与无机碳积累能力的出现有关；(2)确定相应抗原在细胞内的位置；(3)确定缺乏无机碳积累能力的突变衣藻是否含有与这些抗体免疫交叉反应的多肽；(4)研究“诱导”二氧化碳浓缩系统过程中“空气特异性”多肽可翻译mRNA的出现。在富含二氧化碳的细胞适应限制二氧化碳的过程中，差异表达的基因将通过cDNA文库的差异筛选来鉴定，如果时间允许，还可以通过“空气诱导”多肽对应基因的分子克隆来鉴定。所有目标的实现将使我们能够更好地评估将二氧化碳浓缩系统转移到更高的工厂的潜力。有些藻类可以吸收溶解在水中的二氧化碳并进行光合作用。它们如何浓缩溶解气体尚不清楚，但可能是将其引入高等植物的一个重要特征。本研究探讨了植物吸收机理及其对光合作用的促进作用

By comparison with C3 plants, Chlamydomonas reinhardtii and other unicellular algae exhibit unusual photosynthetic characteristics. It has been proposed that these characteristics result from the operation of a CO2- concentrating system, which increases the intracellular CO2 concentration to a level which suppresses photorespiration by competitive inhibition of RuBP oxygenase. One of the principal components of the proposed system is a protein which catalyzes the active transport of inorganic carbon across either the plasmalemma or the chloroplast envelope. However, direct, physical evidence for the existence of this transporter, or any other component of the CO2-concentrating system other than carbonic anhydrase, is lacking. Activity of the CO2-concentrating system is under environmental control. Cells grown at limiting CO2 concentrations (air- adapted) show activity, but cells grown at elevated CO2 concentrations (CO2-enriched) show no activity of the CO2- concentrating system. We have identified 7 polypeptides which increase in abundance during adaptation to limiting CO2 concentrations or are specific for cells grown under such conditions. We will continue to extend these observations to comparisons between wild-type and mutants of Chlamydomonas deficient in the CO2-concentrating system to help identify which polypeptides might be involved directly in inorganic carbon accumulation. Using antibodies generated against one or more of these "air-specific" polypeptides, we expect to: (1) determine whether appearance of the "air-specific" polypeptides during "induction" of the CO2-concentrating system correlates with the appearance of the capacity for inorganic carbon accumulation, (2) determine the intracellular location of the corresponding antigens, (3) determine whether Chlamydomonas mutants deficient in the capacity for inorganic carbon accumulation contain polypeptides immunologically cross-reactive with these antibodies, (4) investigate the appearance of translatable mRNA for "air-specific" polypeptides during the "induction" of the CO2-concentrating system. Genes differentially expressed during adaptation of CO2-enriched cells to limiting CO2 will be identified by differential screening of a cDNA library and, if time permits, by molecular cloning of the genes corresponding to the "air-induced" polypeptides. Attainment of all objectives will allow us to better assess the potential for transferring the CO2-concentrating system into higher plants. Some algae can take up carbon dioxide dissolved in water and photosynthesize sugars. How they concentrate the dissolved gas is unknown but could be an important trait to introduce into higher plants. This work investigates the mechanism of uptake and its subsequent enhancement of photosynthesis.***//