Retrotransposition facilitated the establishment of a primary plastid in the thecate amoeba Paulinella

Victoria Calatrava, Timothy G. Stephens, Arwa Gabr, Devaki Bhaya, Debashish Bhattacharya, Arthur R. Grossman

Research output: Contribution to journalArticlepeer-review

5 Scopus citations


The evolution of eukaryotic life was predicated on the development of organelles such as mitochondria and plastids. During this complex process of organellogenesis, the host cell and the engulfed prokaryote became genetically codependent, with the integration of genes from the endosymbiont into the host nuclear genome and subsequent gene loss from the endosymbiont. This process required that horizontally transferred genes become active and properly regulated despite inherent differences in genetic features between donor (endosymbiont) and recipient (host). Although this genetic reorganization is considered critical for early stages of organellogenesis, we have little knowledge about the mechanisms governing this process. The photosynthetic amoeba Paulinella micropora offers a unique opportunity to study early evolutionary events associated with organellogenesis and primary endosymbiosis. This amoeba harbors a “chromatophore,” a nascent photosynthetic organelle derived from a relatively recent cyanobacterial association (∼120 million years ago) that is independent of the evolution of primary plastids in plants (initiated ∼1.5 billion years ago). Analysis of the genome and transcriptome of Paulinella revealed that retrotransposition of endosymbiont-derived nuclear genes was critical for their domestication in the host. These retrocopied genes involved in photo-protection in cyanobacteria became expanded gene families and were “rewired,” acquiring light-responsive regulatory elements that function in the host. The establishment of host control of endosymbiont-derived genes likely enabled the cell to withstand photo-oxidative stress generated by oxygenic photosynthesis in the nascent organelle. These results provide insights into the genetic mechanisms and evolutionary pressures that facilitated the metabolic integration of the host–endosymbiont association and sustained the evolution of a photosynthetic organelle.

Original languageEnglish (US)
Article numbere2121241119
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number23
StatePublished - Jun 7 2022

All Science Journal Classification (ASJC) codes

  • General


  • endosymbiotic gene transfer
  • gene domestication
  • high light–inducible
  • organellogenesis
  • primary endosymbiosis


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