Adaptive evolution of C4 photosynthesis through recurrent lateral gene transfer

C4 photosynthesis is a complex trait that confers higher productivity under warm and arid conditions. It has evolved more than 60 times via the co-option of genes present in C3 ancestors followed by alteration of the patterns and levels of expression, and adaptive changes in the coding sequences, but the evolutionary path to C4 photosynthesis is still poorly understood. The grass lineage Alloteropsis offers unparalleled opportunities for studying C4 evolution, because it includes a C3 taxon and five C4 species that vary significantly in C4 anatomy and biochemistry. Using phylogenetic analyses of nuclear genes and leaf transcriptomes, we show that fundamental elements of the C4 pathway in the grass lineage Alloteropsis were acquired via a minimum of four independent lateral gene transfers from C4 taxa that diverged from this group more than 20 million years ago. The transfer of genes that were already fully adapted for C4 function has occurred periodically over at least the last 10 milli...C4光合作用（C4 photosynthesis）是一类复杂性状，可在温暖干旱的环境下赋予更高的光合生产力。该性状已独立演化超过60次，具体路径包括招募C3祖先物种中固有的基因，随后调整其表达模式与表达水平，并对编码序列进行适应性改造，但目前学界对C4光合作用的完整演化路径仍不甚明晰。禾本科变源禾属（Alloteropsis）类群为C4演化研究提供了无与伦比的契机：该类群包含1个C3类群与5个C4物种，这些物种在C4解剖结构与生化途径上存在显著差异。本研究通过核基因与叶片转录组的系统发育分析证实，变源禾属中C4途径的核心组分，至少通过四次独立的侧向基因转移，从该类群2000万年前即已分化的C4类群中获得。那些已完全适配C4功能的基因的转移，至少在过去1000万年间周期性地发生过……