Expansion of the redox-sensitive proteome coincides with the plastid endosymbiosis.

The redox-sensitive proteome (RSP) consists of protein thiols that undergo redox reactions, playing an important role in coordinating cellular processes. Here, we applied a large-scale phylogenomic reconstruction approach in the model diatom Phaeodactylum tricornutum to map the evolutionary origins of the eukaryotic RSP. The majority of P. tricornutum redox-sensitive cysteines (76%) is specific to eukaryotes, yet these are encoded in genes that are mostly of a prokaryotic origin (57%). Furthermore, we find a threefold enrichment in redox-sensitive cysteines in genes that were gained by endosymbiotic gene transfer during the primary plastid acquisition. The secondary endosymbiosis event coincides with frequent introduction of reactive cysteines into existing proteins. While the plastid acquisition imposed an increase in the production of reactive oxygen species, our results suggest that it was accompanied by significant expansion of the RSP, providing redox regulatory networks the ability to cope with fluctuating environmental conditions.