The isolation of high molecular mass DNA from the prochlorophyte Prochloron didemni

IsProchlorothrix hollandica the best choice as a prokaryotic model for higher plant Chla/b photosynthesis?

We examine the issue of prochlorophyte origins and provide analyses which highlight the limitations of inferring evolutionary trees from anciently diverged sequences that have markedly different GC contents. Under these conditions we have found that current tree reconstruction methods strongly group together sequences with similar GC contents, whether or not the sequences share a common ancestor. We provide 3'psbA termini sequence forProchloron didemni and find it does not have the 7 amino acid deletion that occurs in Chla/b chloroplasts andProchlorothrix hollandica. This is consistent with the recent findings of a Chlc like pigment in the light harvesting system in other prochlorophytes but apparently absent inP. hollandica. From these observations we suggest thatP. hollandica is the prochlorophyte most closely related to Chla/b containing chloroplasts and hence the most appropriate prokaryotic model for higher plant Chla/b photosynthesis.