title: Cymbomonas tetramitiformis -a peculiar prasinophyte with a taste for bacteria sheds light on plastid evolution.
abstract: Cymbomonas tetramitiformisis a peculiar green alga that unites in one cell the abilities of photosynthesis and phagocytosis, which makes it a very useful model for the study of the evolution of plastid endosymbiosis. We have pondered over this issue and propose an evolutionary scenario of trophic strategies in eukaryotes, including primary and secondary plastid endosymbioses.C. tetramitiformisis a prototroph, just like the common ancestor of Archaeplastida was, and can synthesize most small organic molecules contrary to other eukaryotic phagotrophs, e.g. some metazoans, amoebozoans, and ciliates, which have not evolved tight endosymbiotic relationships. In order to establish a permanent photosynthetic endosymbiont they do not have to become prototrophs, but have to acquire the genes necessary for plastid retention via horizontal (including endosymbiotic) gene transfer. Such processes occurred successfully in the ancestors of eukaryotes with permanent secondary plastids and thus led to their great diversification. The preservation of phagocytosis inCymbomonas(and some other prasinophytes as well) seems to result from nutrient deficiency in their oligotrophic habitats. This forces them to supplement their diet with phagocytized prey, in contrasts to the thecate amoebaPaulinella chromatophora, which also successfully transformed cyanobacteria into permanent organelles. AlthoughPaulinellaendosymbionts were acquired very recently in comparison to primary plastids,Paulinellahas lost the ability to phagocytose, most probably due to the fact that it inhabits nutrient-rich environments, which renders the phagotrophy nonessential.
authors.affiliation: Department of Genomics, Faculty of Biotechnology, University of Wrocław, ul. Joliot-Curie 14A, 50-383 Wrocław, Poland.
authors.forename: Przemysław
authors.initials: P
authors.lastname: Gagat
authors.affiliation: Department of Genomics, Faculty of Biotechnology, University of Wrocław, ul. Joliot-Curie 14A, 50-383 Wrocław, Poland.
authors.forename: Paweł
authors.initials: P
authors.lastname: Mackiewicz
keywords: Cymbomonas; Endosymbiosis; Green algae; Mixotrophy; Paulinella; Phagocytosis