How Really Ancient Is Paulinella Chromatophora?

Abstract

The ancestor of Paulinella chromatophora established a symbiotic relationship with cyanobacteria related to the Prochloroccocus/Synechococcus clade. This event has been described as a second primary endosymbiosis leading to a plastid in the making. Based on the rate of pseudogene disintegration in the endosymbiotic bacteria Buchnera aphidicola, it was suggested that the chromatophore in P. chromatophora has a minimum age of ~60 Myr. Here we revisit this estimation by using a lognormal relaxed molecular clock on the 18S rRNA of P. chromatophora. Our time estimates show that depending on the assumptions made to calibrate the molecular clock, P. chromatophora diverged from heterotrophic Paulinella spp. ~ 90 to 140 Myr ago, thus establishing a maximum date for the origin of the chromatophore. Funding StatementBPZ wishes to thank CINVESTAV Irapuato for funding and support. The authors also declare that no competing interests exist.

Horizontal and endosymbiotic gene transfer in early plastid evolution

“…) adopted a primary photosynthetic organelle (called a chromatophore) by the endosymbiosis of a cyanobacterium from the Synechococcus/Prochlorococcus (Syn/Pro) clade (Marin et al ., ). Paulinella is a good model in which to study the early evolution of primary plastids as the divergence of the chromatophore from its Syn/Pro ancestor is relatively recent, only 90–140 Ma (Delaye et al ., ). Remarkably, there are important similarities between primary endosymbioses in Archaeplastida and Paulinella , likely to have been due to convergent evolution in the process of plastid acquisition (Table ).…”

Evidence supporting an antimicrobial origin of targeting peptides to endosymbiotic organelles

“…Further support for the view that both mitochondrial and chloroplast primary endosymbioses result from bacteria that became resistant to the attack of AMPs via an 'import and destroy' mechanism comes from recent studies with the amoeba Paulinella chromatophora. P. chromatophora acquired a novel primary endosymbiotic organelle called "chromatophore" approximately 100 million years ago (Delaye et al 2016). Proteomic analysis of these chromatophores identified a large set of imported AMP-like peptides as well as chromatophore-imported proteins harboring common N-terminal sequences containing AMP-like motifs (Singer et al 2017).…”

Large DNA virus promoted the endosymbiotic evolution to make a photosynthetic eukaryote

“…To estimate gene transfer timing, the branching time point when P. micropora MYN1 separated from the nearest non-rhizarian organisms in the ML phylogenetic tree was calculated using the RelTime method 55 . We used an estimated value of the divergence of P. micropora and P. chromatophora (45.7–64.7 MYA) based on the 18S rRNA phylogenetic tree corrected by fossil information 11,60 .…”

“…Due to this ancientness, it remains unclear how this evolutionary process proceeded. To unveil this mystery, we analysed the whole genome sequence of a photosynthetic rhizarian amoeba 4 , Paulinella micropora 5,6 , which has a chloroplast-like organelle that originated from another cyanobacterial endosymbiosis 7-10 about 0.1 billion years ago 11 . Here we show that the predacious amoeba that engulfed cyanobacteria evolved into a photosynthetic organism very quickly in the evolutionary time scale, probably aided by the drastic genome reorganization activated by large DNA virus.…”