The Structure and Function of Plastids

Volume 23 of the series Advances in Photosynthesis and Respiration pp 451-473

The Kleptoplast

  • Mary E. RumphoAffiliated withDepartment of Biochemistry, Microbiology and Molecular Biology, University of Maine
  • , Farahad P. DastoorAffiliated withDepartment of Biochemistry, Microbiology and Molecular Biology, University of Maine
  • , James R. ManhartAffiliated withDepartment of Biology, Texas A&M University
  • , Jungho LeeAffiliated withSchool of Biological Sciences, Seoul National University

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Kleptoplasty, the process by which a typically heterotrophic organism acquires and retains chloroplasts from a photosynthetic organism, is quite widespread in ciliates, foraminifera and sacoglossans and variable in terms of longevity and functionality. The sacoglossans are the only group of metazoans which have been shown to harbor functional plastids intracellularly. The ability of the sea slug Elysia chlorotica to “steal” algal chloroplasts, retain them intracellularly, and then integrate the foreign organelles with the sea slug’s metabolism allowing the animal to survive photoautotrophically for months, is unprecedented and for the most part, currently unexplainable. Equally remarkable is the stability and adaptability of the chloroplasts; they not only survive the ingestion process and resist digestion by the host, but they also adjust osmotically and metabolically to the entirely new cellular environment devoid of any new protective membrane. The biochemistry of such an association is intriguing because of the evidence supporting the reliance of normal chloroplasts on the nucleus to encode the great majority of their proteins and regulate the expression of chloroplast encoded proteins. There appear to be no algal nuclei in E. chlorotica and the chloroplast genome of V. litorea does not have an unusual coding capacity to account for all of the nuclear encoded chloroplast targeted proteins necessary to sustain the observed chloroplast activity. Preliminary results supporting lateral gene transfer are encouraging and exciting. It is likely that a combination of organelle/protein stability and lateral gene transfer play key roles in sustaining this fascinating association in sacoglossan molluscs.