Foreign Organelle Retention and Endocytobiosis in Protists
Both Foreign Organelle Retention (FOR) and algal endocytobiosis are found in diverse protist taxa and in some animals. FOR refers to the temporary sequestration of cellular organelles of one species by the cells of another. Such organelles are usually obtained during feeding with selective digestion. Examples include the retention of plastids (sometimes called "kleptoplasty" or "kleptoplastidy") and of nuclei ("karyoklepty") based on the somewhat anthropomorphic notion that the organelles in question are "stolen." Other foreign organelles, including mitochondria and nematocysts may also be retained.
FOR is distinguished from endocytobiosis (intracellular endosymbiosis) since organelles rather than intact cells are retained. However, a sharp line between the two may be difficult to draw in cases of multiple FOR where a partial structural integrity of the source cells remains. FOR, however, is also distinguished from permanent inherited endocytobiosis by its temporary nature. There is wide variation in the duration of retention of foreign organelles. In the case of organelles such as plastids and mitochondria, whose genomes contain only a fraction of the genes required for their function, cases of long-term retention imply mechanisms of maintenance. Examples include the presence of suitable genes in host cell nuclei, concomitant retention of transcriptionally active foreign nuclei, organelle protein import mechanisms, and an unusual stability of organelle proteins.
Mitochondria and primary plastids are known to have evolved from permanent bacterial endocytobionts. Furthermore, successive endocytobioses of plastid-bearing eukaryotes within other eukaryotic hosts have led, by processes of endosymbiotic gene transfer and structural reduction, to the secondary and tertiary plastids now found in diverse algal lineages.
Symbiogenesis, as first defined by K. S. Mereschovsky in 1909, is the origin of new species as a consequence of symbiosis. Foreign plastid retention, algal endocytobiosis, and permanent plastids can each be understood as lying along a continuum of symbiogenetic evolution. Therefore, study of foreign plastid retention and maintenance, and of interactions between algal endocytobionts and their hosts may provide insights into possible pathways of secondary and tertiary plastid evolution.
I am studying foreign organelle retention in an Antarctic dinoflagellate that obtains foreign plastids from the alga Phaeocystis antarctica, upon which it feeds selectively.
Both Foreign Organelle Retention (FOR) and algal endocytobiosis are found in diverse protist taxa and in some animals. FOR refers to the temporary sequestration of cellular organelles of one species by the cells of another. Such organelles are usually obtained during feeding with selective digestion. Examples include the retention of plastids (sometimes called "kleptoplasty" or "kleptoplastidy") and of nuclei ("karyoklepty") based on the somewhat anthropomorphic notion that the organelles in question are "stolen." Other foreign organelles, including mitochondria and nematocysts may also be retained.
FOR is distinguished from endocytobiosis (intracellular endosymbiosis) since organelles rather than intact cells are retained. However, a sharp line between the two may be difficult to draw in cases of multiple FOR where a partial structural integrity of the source cells remains. FOR, however, is also distinguished from permanent inherited endocytobiosis by its temporary nature. There is wide variation in the duration of retention of foreign organelles. In the case of organelles such as plastids and mitochondria, whose genomes contain only a fraction of the genes required for their function, cases of long-term retention imply mechanisms of maintenance. Examples include the presence of suitable genes in host cell nuclei, concomitant retention of transcriptionally active foreign nuclei, organelle protein import mechanisms, and an unusual stability of organelle proteins.
Mitochondria and primary plastids are known to have evolved from permanent bacterial endocytobionts. Furthermore, successive endocytobioses of plastid-bearing eukaryotes within other eukaryotic hosts have led, by processes of endosymbiotic gene transfer and structural reduction, to the secondary and tertiary plastids now found in diverse algal lineages.
Symbiogenesis, as first defined by K. S. Mereschovsky in 1909, is the origin of new species as a consequence of symbiosis. Foreign plastid retention, algal endocytobiosis, and permanent plastids can each be understood as lying along a continuum of symbiogenetic evolution. Therefore, study of foreign plastid retention and maintenance, and of interactions between algal endocytobionts and their hosts may provide insights into possible pathways of secondary and tertiary plastid evolution.
I am studying foreign organelle retention in an Antarctic dinoflagellate that obtains foreign plastids from the alga Phaeocystis antarctica, upon which it feeds selectively.
