Department of Botany, University of British Columbia, Vancouver, British Columbia, Canada.
Department of Biology, University of Victoria, Victoria, British Columbia, Canada.
Nature. 2019 Aug;572(7768):240-243. doi: 10.1038/s41586-019-1398-6. Epub 2019 Jul 17.
Rhodophyta (red algae) is one of three lineages of Archaeplastida, a supergroup that is united by the primary endosymbiotic origin of plastids in eukaryotes. Red algae are a diverse and species-rich group, members of which are typically photoautotrophic, but are united by a number of highly derived characteristics: they have relatively small intron-poor genomes, reduced metabolism and lack cytoskeletal structures that are associated with motility, flagella and centrioles. This suggests that marked gene loss occurred around their origin; however, this is difficult to reconstruct because they differ so much from the other archaeplastid lineages, and the relationships between these lineages are unclear. Here we describe the novel eukaryotic phylum Rhodelphidia and, using phylogenomics, demonstrate that it is a closely related sister to red algae. However, the characteristics of the two Rhodelphis species described here are nearly opposite to those that define red algae: they are non-photosynthetic, flagellate predators with gene-rich genomes, along with a relic genome-lacking primary plastid that probably participates in haem synthesis. Overall, these findings alter our views of the origins of Rhodophyta, and Archaeplastida evolution as a whole, as they indicate that mixotrophic feeding-that is, a combination of predation and phototrophy-persisted well into the evolution of the group.
红藻门（red algae）是古生菌超群的三个谱系之一，古生菌超群通过真核生物中质体的初级内共生起源而联合在一起。红藻是一个多样化且物种丰富的群体，其成员通常为光自养生物，但它们具有一些高度衍生的特征：它们的基因组相对较小，内含子较少，新陈代谢减少，并且缺乏与运动、鞭毛和中心粒相关的细胞骨架结构。这表明在它们的起源周围发生了明显的基因丢失；然而，由于它们与其他古生菌谱系差异很大，并且这些谱系之间的关系不清楚，因此很难重建。在这里，我们描述了新的真核生物门 Rhodelphidia，并通过系统基因组学证明它与红藻密切相关。然而，这里描述的两种 Rhodelphis 物种的特征几乎与定义红藻的特征相反：它们是非光合作用的、有鞭毛的掠食者，具有基因丰富的基因组，以及可能参与血红素合成的原始质体缺失的遗迹。总的来说，这些发现改变了我们对红藻起源以及整个古生菌进化的看法，因为它们表明混合营养喂养——即捕食和光合作用的结合——在该群体的进化过程中一直存在。
