Madeleine Cook and Tiffany Irizarry
Critical Review “Transcriptomic Evidence that Longevity of Acquired Plastids in the
Photosynthetic slugs Elysia timida & Plakobranchus ocelatur does not entail lateral
transfer of algal nuclear genes.”
Sacoglossan sea slugs are unique in that they sequester and maintain active
plastics that they acquire from the siphonaceous algae upon which they feed, further
making the animals photosynthetic. This study was investigating how these sea
slugs are able to retain their stolen plastids (kleptoplast) in such a
photosynthetically active state for weeks and months. It is widely thought that the
maintenance of these chloroplast involve some sort of gene transfer from the algal
food source to the slugs based upon previous investigations. Furthermore this study
was essential in particular because it contradicted Rumpho’s results, which
indicated that an algal nuclear gene (psbO) was horizontally transferred to the sea
slug Elysia chlorotica and therefore was responsible for kleptoplast’s maintenance
within sea slugs.
This study used a deep-sequencing approach to focus on expressed genes
from the photosynthesizing, in order to identify expressed genes that might have
been acquired from algae. Their results revealed that two different species of
sacoglossan slugs (Elysia timida & Plakobranchus ocelatur) did not express any
genes acquired from algal nuclei in order to maintain their sequestered plastid’s
function. Thus leaving the molecular basis for plastid maintenance within the
cytosol of digestive gland cells in these photosynthetic metazoans unknown.