Horizontal and endosymbiotic gene transfer in early plastid evolution

Area of Science:

• Evolutionary Biology
• Cell Biology
• Genomics

Background:

• Plastids originated from a primary endosymbiotic event involving a cyanobacterium and a eukaryotic host.
• Secondary endosymbiosis, where algae are engulfed by other eukaryotes, has significantly driven the diversification of photosynthetic eukaryotes.
• The genetic makeup of plastids is not solely derived from their cyanobacterial ancestor.

Purpose of the Study:

• To investigate the mosaic origin of plastid-related genes in nuclear genomes.
• To understand the contribution of host and non-cyanobacterial bacterial genes to plastid function.
• To explore the genetic complexity underlying secondary plastid acquisition, particularly in green algae.

Main Methods:

• Analysis of nuclear genomes from plastid-bearing eukaryotic lineages.
• Comparative genomics to identify gene origins (cyanobacterial, host, other bacterial).
• Investigating gene recruitment for plastid-localized metabolic pathways.

Main Results:

• Plastids possess a mosaic of genes from cyanobacteria, the eukaryotic host nucleus, and non-cyanobacterial bacteria.
• Plastid proteins and metabolic pathways evolved through the "tinkering" of gene toolkits from diverse sources.
• The "red carpet hypothesis" suggests prior red algal gene acquisition facilitated the "red carpet" for green plastid acquisition in some secondary algae.

Conclusions:

• Plastid evolution is characterized by extensive gene acquisition from multiple sources, leading to a complex genetic heritage.
• This genetic "tinkering" has been crucial for the evolution and diversification of plastid-bearing organisms.
• Understanding this mixed heritage is key to deciphering the evolutionary trajectories of algae and their impact on global ecosystems.