On the origin of plastids: new insights from elusive marine microbes
The origin of the photosynthetic organelles–the plastids–in eukaryotes, some 1.5-2 billion years ago, was one of the most transformative events in the history of life. It resulted in an explosion of diversity of trees and all eukaryotic algae, allowing life as we know it to evolve. Despite this critical importance, however, we still know little of the evolution of the early photosynthetic eukaryotes. In this presentation, I will first provide a brief review on the origin of plastid by endosymbiosis, and where in the eukaryotic tree of life we find plastids. I will then show how the discovery and recent single-cell genomics of an elusive marine microbial eukaryotic group–the Picozoa–complexifies the current paradigm of plastid origin. I will conclude by presenting a new model of plastid origin that includes a diversity of deep-branching unknown taxa similar to Picozoa, which I argue need to be discovered and accounted for.
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