Plastid Evolution in Non-photosynthetic Lineages

Plastids are endosymbiotic organelles widespread among eukaryotic lineages. They were pivotal in the evolution of eukaryotes, as they allowed host eukaryotic cells to perform photosynthesis. From an evolutionary point of view, there are two main types of plastids, primary and complex (higher-order) plastids. Primary plastids originated through a single event, the engulfment of a cyanobacteria by a eukaryotic host cell, giving rise to the group Archaeplastida (which includes plants). On the other hand, complex plastids, which occur when a primary plastid containing eukaryote is enslaved by another host cell, have originated multiple times within eukaryotes, and have given rise to most other plastid-bearing lineages. The most common function of plastids is photosynthesis, which facilitates carbon fixation using energy from sunlight. However, plastids participate in many essential metabolic processes such as fatty acid metabolismMetabolism, as well as iron–sulfur cluster and isoprenoid synthesis. Similar to mitochondria, where there are many lineages with reduced mitochondrial organelles incapable of oxidative phosphorylation, there are many eukaryotic lineages with plastids that have lost photosynthesis. In this chapter, we will discuss these lineages as well as the genomic changes associated with photosynthesis loss and its evolutionary consequences.