Assessing the bacterial contribution to the plastid proteome

Area of Science:

• * Evolutionary biology
• * Molecular biology
• * Biochemistry

Background:

• * Plastids (e.g., chloroplasts) perform vital functions like photosynthesis and amino acid biosynthesis.
• * These functions depend on proteins from diverse origins: endosymbiotic cyanobacteria, other bacteria, and the eukaryotic host.
• * Understanding protein origins is key to tracing the evolution of Archaeplastida (>1 billion years).

Purpose of the Study:

• * To analyze plastid proteome data from glaucophytes and green algae.
• * To infer protein origins and organelle protein sharing within Archaeplastida.
• * To identify non-cyanobacterial bacterial contributions to plastid proteomes.

Main Methods:

• * Comparative analysis of plastid proteome data.
• * Homology searches to identify protein origins.
• * Mapping of plastid proteins to metabolic pathways.

Main Results:

• * Over one-third of genes encoding plastid proteins lack detectable homologs in Cyanobacteria.
• * Chlamydiae and Proteobacteria are significant bacterial sources of plastid proteins.
• * A core set of ancient proteins exists in Archaeplastida, alongside lineage-specific proteins acquired via horizontal gene transfer (HGT).

Conclusions:

• * Plastid evolution involved extensive gene acquisition from diverse bacterial lineages beyond cyanobacteria.
• * Horizontal gene transfer (HGT) has played a significant role in shaping lineage-specific plastid functions.
• * Plastid proteomes represent a complex mosaic of endosymbiotic, bacterial, and host-derived proteins.