Chloroplast retention in Elysia

August 25, 1999
From: Marc-André Selosse

Hello !

I found your question about Elysia. Please find here two references on the (very long) survival of plastids in Elysia chlorotica:

1. Pierce S, Biron R, Rumpho M. (1996)
Endosymbiotic chloroplasts in molluscan cells contain proteins synthesized after plastid capture. J Exp Biol;199(Pt 10):2323-30

Endosymbiotic chloroplasts within the cells of the ascoglossan slug Elysia chlorotica synthesize a variety of proteins including the large subunit of
ribulose-1,5-bisphosphate-carboxylase oxygenase (RuBisCO) and the photosystem II protein D1. In addition, the effects of protein synthesis inhibitors suggest that some chloroplast-associated proteins are synthesized in the animal cytosol and subsequently translocated into the chloroplasts. Thus, the plastids not only synthesize proteins during this long-lived association, but the host cell seems to play a role in plastid protein turnover.

2. Mujer CV, Andrews DL, Manhart JR, Pierce SK, Rumpho ME (1996) Chloroplast genes are expressed during intracellular symbiotic association of Vaucheria litorea plastids with the sea slug Elysia chlorotica. Proc Natl Acad Sci U S A, 93(22):12333-8

The marine slug Elysia chlorotica (Gould) forms an intracellular symbiosis with photosynthetically active chloroplasts from the chromophytic alga Vaucheria litorea (C. Agardh). This symbiotic association was characterized over a period of 8 months during which E. chlorotica was deprived of V. litorea but provided with light and CO2. The fine structure of the symbiotic chloroplasts remained intact in E. chlorotica even after 8 months of starvation as revealed by electron microscopy. Southern blot analysis of total DNA from E. chlorotica indicated that algal genes, i.e., rbcL, rbcS, psaB, psbA, and 16S rRNA are present in the animal. These genes are typically localized to the plastid genome in higher plants and algae except rbcS, which is nuclear-encoded in higher plants and green (chlorophyll a/b) algae. Our analysis suggests, however, that similar to the few other chromophytes (chlorophyll a/c) examined, rbcS is chloroplast encoded in V.litorea. Levels of psbA transcripts remained constant in E. chlorotica starved for 2 and 3 months and then gradually declined over the next 5 months corresponding with senescence of the animal in culture and in nature.
The RNA synthesis inhibitor 6-methylpurine reduced the accumulation of psbA transcripts confirming active transcription. In contrast to psbA, levels of 16S rRNA transcripts remained constant throughout the starvation period. The levels of the photosystem II proteins, D1 and CP43, were high at 2 and 4 months of starvation and remained constant at a lower steady-state level after 6 months. In contrast, D2 protein levels, although high at 2 and 4 months, were very low at all other periods of starvation. At 8 months, de novo synthesis of several thylakoid membrane-enriched proteins, including D1, still occurred. To our knowledge, these results represent the first molecular evidence for active transcription and translation of algal chloroplast genes in an animal host and are discussed in relation to the endosymbiotic theory of eukaryote origins.

Sincerely yours,

Marc-André

M.-A. SELOSSE
NANCY
FRANCE

ma.selosse@wanadoo.fr

Selosse, M., 1999 (Aug 25) Chloroplast retention in Elysia. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/1244

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