Christin Pascal-Antoine, Besnard Guillaume, Samaritani Emanuela, Duvall Melvin R, Hodkinson Trevor R, Savolainen Vincent, Salamin Nicolas
Department of Ecology and Evolution, Biophore, University of Lausanne, 1015 Lausanne, Switzerland.
Curr Biol. 2008 Jan 8;18(1):37-43. doi: 10.1016/j.cub.2007.11.058. Epub 2007 Dec 20.
C4 photosynthesis is an adaptation derived from the more common C3 photosynthetic pathway that confers a higher productivity under warm temperature and low atmospheric CO2 concentration [1, 2]. C4 evolution has been seen as a consequence of past atmospheric CO2 decline, such as the abrupt CO2 fall 32-25 million years ago (Mya) [3-6]. This relationship has never been tested rigorously, mainly because of a lack of accurate estimates of divergence times for the different C4 lineages [3]. In this study, we inferred a large phylogenetic tree for the grass family and estimated, through Bayesian molecular dating, the ages of the 17 to 18 independent grass C4 lineages. The first transition from C3 to C4 photosynthesis occurred in the Chloridoideae subfamily, 32.0-25.0 Mya. The link between CO2 decrease and transition to C4 photosynthesis was tested by a novel maximum likelihood approach. We showed that the model incorporating the atmospheric CO2 levels was significantly better than the null model, supporting the importance of CO2 decline on C4 photosynthesis evolvability. This finding is relevant for understanding the origin of C4 photosynthesis in grasses, which is one of the most successful ecological and evolutionary innovations in plant history.
C4光合作用是从更常见的C3光合途径衍生而来的一种适应机制，在温暖温度和低大气二氧化碳浓度条件下具有更高的生产力[1,2]。C4进化被视为过去大气二氧化碳下降的结果，比如3200万至2500万年前（Mya）二氧化碳的突然下降[3-6]。这种关系从未得到过严格验证，主要是因为缺乏对不同C4谱系分化时间的准确估计[3]。在本研究中，我们推断出了禾本科植物的一个大型系统发育树，并通过贝叶斯分子定年法估计了17至18个独立的禾本科C4谱系的年龄。从C3光合作用到C4光合作用的首次转变发生在画眉草亚科，时间为32.0 - 25.0 Mya。通过一种新颖的最大似然方法检验了二氧化碳减少与向C4光合作用转变之间的联系。我们表明，纳入大气二氧化碳水平的模型明显优于零模型，这支持了二氧化碳下降对C4光合作用进化能力的重要性。这一发现对于理解禾本科植物中C4光合作用的起源具有重要意义，C4光合作用是植物历史上最成功的生态和进化创新之一。
