Botany Department, Canadian Institute for Advanced Research, University of British Columbia, 3529-6270 University Boulevard, Vancouver, BC, Canada V6T 1Z4.
Philos Trans R Soc Lond B Biol Sci. 2010 Mar 12;365(1541):729-48. doi: 10.1098/rstb.2009.0103.
Plastids and mitochondria each arose from a single endosymbiotic event and share many similarities in how they were reduced and integrated with their host. However, the subsequent evolution of the two organelles could hardly be more different: mitochondria are a stable fixture of eukaryotic cells that are neither lost nor shuffled between lineages, whereas plastid evolution has been a complex mix of movement, loss and replacement. Molecular data from the past decade have substantially untangled this complex history, and we now know that plastids are derived from a single endosymbiotic event in the ancestor of glaucophytes, red algae and green algae (including plants). The plastids of both red algae and green algae were subsequently transferred to other lineages by secondary endosymbiosis. Green algal plastids were taken up by euglenids and chlorarachniophytes, as well as one small group of dinoflagellates. Red algae appear to have been taken up only once, giving rise to a diverse group called chromalveolates. Additional layers of complexity come from plastid loss, which has happened at least once and probably many times, and replacement. Plastid loss is difficult to prove, and cryptic, non-photosynthetic plastids are being found in many non-photosynthetic lineages. In other cases, photosynthetic lineages are now understood to have evolved from ancestors with a plastid of different origin, so an ancestral plastid has been replaced with a new one. Such replacement has taken place in several dinoflagellates (by tertiary endosymbiosis with other chromalveolates or serial secondary endosymbiosis with a green alga), and apparently also in two rhizarian lineages: chlorarachniophytes and Paulinella (which appear to have evolved from chromalveolate ancestors). The many twists and turns of plastid evolution each represent major evolutionary transitions, and each offers a glimpse into how genomes evolve and how cells integrate through gene transfers and protein trafficking.
质体和线粒体各自起源于一次单一的内共生事件，在它们被还原并与宿主整合的方式上有许多相似之处。然而，这两个细胞器的后续进化却大不相同：线粒体是真核细胞的稳定组成部分，既不会丢失，也不会在谱系之间转移；而质体的进化则是一个复杂的混合体，包括运动、丢失和替换。过去十年的分子数据大大理清了这段复杂的历史，我们现在知道质体起源于蓝藻、红藻和绿藻（包括植物）祖先的一次单一内共生事件。红藻和绿藻的质体随后通过二次内共生被转移到其他谱系中。绿藻质体被眼虫和绿藻被甲藻以及一小部分甲藻吸收。红藻似乎只被吸收过一次，产生了一个被称为有色体的多样化群体。此外，还有质体丢失和替换的情况，这至少发生过一次，可能发生过多次。质体丢失很难证明，而且在许多非光合谱系中发现了隐匿的、非光合质体。在其他情况下，现在已经了解到光合谱系是从具有不同起源的祖先进化而来的，因此一个祖先质体被一个新的质体所取代。这种替换发生在几个甲藻（通过与其他有色体的三次内共生或与绿藻的连续二次内共生）中，显然也发生在两个根足虫谱系：绿藻被甲藻和 Paulinella 中（它们似乎是从有色体祖先进化而来的）。质体进化的许多曲折都代表了主要的进化转折点，每个转折点都让我们一窥基因组如何进化，以及细胞如何通过基因转移和蛋白质运输进行整合。
