Chlorarachniophytes are marine protists that have acquired photosynthetic capacity by engulfing and retaining a chlorophyte green alga through secondary endosymbiosis. This process has been an important factor in eukaryotic evolution, yet the number and timing of these events remains unresolved. One of the main results of secondary endosymbiosis has been the movement of the genes encoding plastid-targeted proteins from the endosymbiont nucleus to that of the host.

In the Early edition of PNAS, John Archibald and colleagues from The Canadian Institute for Advanced Research describe phylogenetic analysis of several plastid-targeted proteins from a chlorarachniophytes. They show that a significant number of genes have been acquired through lateral gene transfer from numerous sources, but that the genes of the chlorophyte Chlamydomonas reinhardtii show no evidence of lateral gene transfer (PNAS, DOI:10.1073/pnas.1230951100).

Archibald et al. screened nearly 4,000 ESTs (expressed sequence tags) from the chlorarachniophyte Bigelowiella natans and...

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