Complex Endosymbioses I: From Primary to Complex Plastids, Serial Endosymbiotic Events

Area of Science:

• * Eukaryotic cell biology
• * Endosymbiosis and evolutionary biology
• * Photosynthetic algal diversity

Background:

• * Eukaryotic phototrophs exhibit diverse plastids, many originating from endosymbiotic events between eukaryotes.
• * Complex plastids, characterized by multiple envelope membranes and nucleomorphs, represent chimeric cellular structures.
• * Primary plastids in Archaeplastida evolved from a single cyanobacterial endosymbiosis, distinct from complex plastids.

Purpose of the Study:

• * To summarize knowledge on the acquisition, evolution, and function of complex plastids in algae.
• * To explore the evolutionary pathways and frequency of complex plastid acquisition.
• * To discuss the cellular adaptations and consequences of endosymbiosis, including gene transfer and loss of photosynthesis.

Main Methods:

• * Review and synthesis of existing scientific literature on algal endosymbiosis.
• * Comparative analysis of plastid evolution across different eukaryotic lineages.
• * Examination of genetic and cellular evidence for endosymbiotic events and gene transfer.

Main Results:

• * Complex plastids arose independently multiple times in eukaryotic lineages, particularly in the green and red algae lineages.
• * Secondary and higher-order endosymbioses are common mechanisms for acquiring complex plastids, leading to plastid replacements.
• * Endosymbiosis involves massive gene transfer from endosymbiont to host and significant cellular adaptations, often resulting in loss of photosynthetic capability.

Conclusions:

• * Complex plastids are a result of frequent, independent endosymbiotic events between eukaryotic cells.
• * The acquisition of complex plastids involves intricate genetic and cellular integration processes.
• * Despite the photosynthetic advantage, many algae with complex plastids have lost photosynthesis, highlighting evolutionary flexibility.