摘要：SummaryThe primary plastid endosymbiosis (∼124 Mya) that occurred in the heterotrophic amoeba lineage,Paulinella, is at an earlier stage of evolution than in Archaeplastida, and provides an excellent model for studying organelle integration. Using genomic data from photosyntheticPaulinella, we identified a plausible mechanism for the evolution of host control of endosymbiont (termed the chromatophore) biosynthetic pathways and functions. Specifically, random gene loss from the chromatophore and compensation by nuclear-encoded gene copies enables host control of key pathways through a minimal number of evolutionary innovations. These gene losses impact critical enzymatic steps in nucleotide biosynthesis and the more peripheral components of multi-protein DNA replication complexes. Gene retention in the chromatophore likely reflects the need to maintain a specific stoichiometric balance of the encoded products (e.g., involved in DNA replication) rather than redox state, as in the highly reduced plastid genomes of algae and plants.Graphical abstractDisplay OmittedHighlights•Endosymbiont DNA replication cannot be completed without several key host proteins•Endosymbiont nucleotide biosynthesis is completed by import of host proteins•Limited gene loss allowed the host to gain control of endosymbiont division•Paulinellaregulates chromatophore function using the stringent response pathwayBiological sciences; Genetics; Evolutionary biology
