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nucleomorph
Nucleomorphs are small, vestigial eukaryotic nuclei found between the inner and outer pairs of membranes in certain plastids. They are thought to be vestiges of primitive red and green algal nuclei that engulfed a prokaryote (plastid). Because the nucleomorph lies between two sets of membranes, nucleomorphs support the endosymbiotic theory and are evidence that the plastids containing them are complex plastids. Having two sets of membranes indicate that the plastid, a prokaryote, was engulfed by a eukaryote, an alga, which was then engulfed by another eukaryote, the host cell, making the plastid an example of secondary endosymbiosis. 〔Archibald, J.M., and C.E. Lane. "(Going, Going, Not Quite Gone: Nucleomorphs as a Case Study in Nuclear Genome Reduction )." ''Journal of Heredity'' 100.5 (2009): 582-90.〕〔 Reyes-Prieto, Adrian, Andreas P.M. Weber, and Debashish Bhattacharya. "(The Origin and Establishment of the Plastid in Algae and Plants )." ''Annual Review of Genetics'' 41.1 (2007): 147-68.〕
==Organisms with known nucleomorphs==
So far, only two groups of organisms are known to contain plastids with a vestigal nucleus or nucleomorph: the cryptomonads of the supergroup Chromista and the chlorarachniophytes of the supergroup Rhizaria, both of which have examples of sequenced nucleomorph genomes.〔〔 Studies of the genomic organization and of the molecular phylogeny have shown that the nucleomorph of the cryptomonads formerly was the nucleus of a red alga, whereas the nucleomorph of the chlorarchniophytes formerly was the nucleus of a green alga. In both groups of organisms the plastids originate from engulfed photoautotrophic eukaryotes.
Of the two known plastids that contain nucleomorphs, both have four membranes, the nucleomorph residing in the periplastidial compartment, evidence of being engulfed by a eukaryote through phagocytosis.〔
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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