植物登陆过程中光合作用相关基因的进化

摘要

现代陆生植物的祖先大约在5亿到4．7亿年前登陆，这是植物进化过程中的重要事件。光照不仅是植物的主要能量来源，还是主要的环境信息来源之一。一般认为，光合作用效率越高，植物的适应能力越强。植物登陆过程前后，环境从光照、光强到二氧化碳／氧气浓度比等都发生了变化，比如适应陆地生活的海草重新返回水生环境，猜测在这个过程中植物光合作用的相关的关键功能基因可能发生了进化。为了证明该假说，以链形植物门绿藻和低等陆地植物为主要研究对象，通过从GenBank收集相关基因序列以及从几株相近绿藻中提取测定DNA序列，利用PAML“分枝－位点”模型对光合作用光反应和暗反应中的psbA、rbcL、rca 3个基因进行了适应性进化分析。结果显示植物登陆过程前后，在这3个光合作用相关基因中均未检测到统计上显著的正选择位点，反而在绿色植物早期分化（绿藻门和链形植物门）过程中却发现有明显的正选择痕迹。这些惊人的结果提示植物登陆前后从水体到陆地的环境变化对光合作用的影响可能并不大，其它诸如角质膜、气孔器等相关的基因可能发挥了更大的作用。%The ancestors of modern land plants colonized the terrestrial habitat about 500 to 470 million years ago , this is an important event in the history of life on earth .Illumination is not only the primary energy for plants , but also the main environmental information sources.It is widely accepted that the higher efficiency of photosynthesis , the stronger ability of plants to adapt the environment .When plants began to colonize the terrestrial habitat , their environment significantly changed , such as illumination , light intensity and the concentration ratio of carbon dioxide and oxygen just like seagrasses went back to the sea .Therefore , we hypothesize that there are evi-dences for adaptive evolution of photosynthesis-related genes in plants .To test this hypothesis , detection of adaptive evolution was per-formed on psbA, rbcL, rca genes using PAML′s"site-branch"model.As a result, no significant evidence of positive selection of these three genes was detected in the plant colonization , whereas there was remarkable divergence between Chlorophyta and Streptophyta. This amazing result implies that environmental changes during plants colonizing the terrestrial habitat may have few influences on photo -synthesis-related genes .Genes related to other functions like cuticle and stomatal apparatus played important roles in this course .