Genome analysis reveals chloroplast acquisition without gene transfer in photosynthetic sea slugs
Plants, algae and some bacteria are able to perform photosynthesis, which is the process of transforming sunlight energy into sugar. Animals are generally unable to use this process to acquire energy, but there are a few known exceptions to this. Some sea slugs take up chloroplasts from the algae that they consume into their cells. These chloroplasts retain their ability to perform photosynthetic activity within the animal cells for several months, and thus provide them with photosynthesis-derived nutrition. This process is called "kleptoplasty," and it has attracted much attention due to its amazing uniqueness in making animals photosynthetic for over 50 years.
A pressing question is how these sequestered chloroplasts retains their photosynthetic capability without algal nuclei. Since the genome of the algal nucleus encodes most of the proteins required for photosynthesis, chloroplasts isolated from algal cells instantly lose their photosynthetic capability. Nevertheless, algae-eating sea slugs retain this photosynthetic capability for months. There have been numerous debates about the mechanisms underlying the phenomenon of sequestered chloroplasts retaining photosynthetic capabilities over the long term. A widely accepted hypothesis accounting for kleptoplasty is the horizontal gene transfer of the photosynthesis genes from algae to sea slug.