Elysia chlorotica, pictured right, is a green sea slug that lives along the Atlantic coastline of the United States. What makes this slug so unique is that it is able to ingest a certain species of algae (called Vaucheria litorea), store the algae's chloroplasts in the cells lining its gut, then run on "solar power" (i.e. convert sunlight into energy) for much of its life. Plant? Animal? Or freak?
The very fact that this slug can photosynthesise from ingested chloroplasts is perplexing; you see, the chloroplasts themselves contain only enough DNA to encode for about 10% of the proteins required for photosynthesis. Rumpho and her team hypothesised that the sea slug incorporates some of the algal DNA into its own DNA in a process called kleptoplasty. It is still, however, unclear as to how this occurs, but one theory is that some algal DNA is absorbed, along with the plastids, in the slug's gut.
Rumpho and her colleagues first sequenced the plastid genome of Vaucheria litorea and confirmed that it lacks the full complement of genes needed for photosynthesis. Then, to demonstrate the fact that the predator does indeed incorporate algal DNA into its own DNA, they showed that the nuclear gene of oxygenic photosynthesis, psbO, is expressed in the nuclear DNA of the sea slug. Furthermore, it was revealed that the psbO of the V. litorea is identical to that of the E. chlorotica, but absent in the mitochondrial genome of the latter organism.
The researchers believe that many more photosynthetic genes are absorbed by the sea slug through its diet, but do not completely understand as to how such plant genes are activated within the animal's cells.
Original article:
Additional information:
PNAS - Horizontal gene transfer of the algal nuclear gene psbO to the photosynthetic sea slug Elysia chlorotica
Author:
Insoo Kim (42050911), BIOL1020 P2
