Independent and parallel evolution of new genes by gene duplication in two origins of C4 photosynthesis provides new insight into the mechanism of phloem loading in C4 species

C4 photosynthesis is considered one of the most remarkable examples of evolutionary convergence in eukaryotes. However, it is unknown whether the evolution of C4 photosynthesis required the evolution of new genes. Genome-wide gene-tree species-tree reconciliation of seven monocot species that span two origins of C4 photosynthesis revealed that there was significant parallelism in the duplication and retention of genes coincident with the evolution of C4 photosynthesis in these lineages. Specifically, 21 orthologous genes were duplicated and retained independently in parallel at both C4 origins. Analysis of this gene cohort revealed that the set of parallel duplicated and retained genes is enriched for genes that are preferentially expressed in bundle sheath cells, the cell type in which photosynthesis was activated during C4 evolution. Furthermore, functional analysis of the cohort of parallel duplicated genes identified SWEET-13 as a potential key transporter in the evolution of C4 pho...

C4光合途径（C4 photosynthesis）被认为是真核生物中最显著的进化趋同现象之一。然而目前仍未明确C4光合途径的演化是否需要新基因的起源。针对涵盖两次C4光合途径独立起源事件的7个单子叶植物物种，研究人员开展了全基因组基因树-物种树调和分析（genome-wide gene-tree species-tree reconciliation），结果表明，在这些演化谱系中，与C4光合途径演化同步发生的基因复制与保留事件呈现出显著的平行性。具体而言，共有21个直系同源基因（orthologous genes）在两次C4起源事件中独立发生了平行复制与保留。对该基因集合的分析结果显示，这类平行复制并保留的基因显著富集于在维管束鞘细胞（bundle sheath cells）中偏好表达的基因——维管束鞘细胞正是C4演化过程中光合作用被激活的核心细胞类型。此外，对该平行复制基因集合的功能分析鉴定出SWEET-13是C4光合途径演化过程中潜在的关键转运蛋白