The sea slug, Elysia chlorotica, can transform into plant like and survive just on photosynthesis. The undertaking is highly unusual for an animal but the mollusk somehow manages to steal millions of green-colored plastids, which are like tiny solar panels, from the non-toxic brown alga, store them in their gut lining, and become photosynthetic, or solar-powered.

“It’s a remarkable feat because it’s highly unusual for an animal to behave like a plant and survive solely on photosynthesis,” said Debashish Bhattacharya, senior author of the study in a news release.

“The broader implication is in the field of artificial photosynthesis. That is, if we can figure out how the slug maintains stolen, isolated plastids to fix carbon without the plant nucleus, then maybe we can also harness isolated plastids for eternity as green machines to create bioproducts or energy. The existing paradigm is that to make green energy, we need the plant or alga to run the photosynthetic organelle, but the slug shows us that this does not have to be the case.”

Sea Slug, Elysia chlorotica [ Image: Karen N. Pelletreau/University of Maine]

The brown alga, Vaucheria litore, is an ideal food source for the sea slug. The lack of walls between adjoining cells in its body make it easy for the slug to destroy its outer cell wall and channel through its interior and suck out the cell contents and gather all of the algal nuclei and plastids at once. Some scientists argue that Elysia chlorotica steal and store plastids as food to be used later, much like camels store fat in their humps. But the findings showed that’s not the case.

“It has this remarkable ability to steal these algal plastids, stop feeding and survive off the photosynthesis from the algae for the next six to eight months,” Bhattacharya said.

The team had the slug’s RNA sequenced (gene expression) and tested their solar energy supply hypothesis. The data showed the slug reacted to protect the stolen plastids from digestion and turned on animal genes to “utilize the algal photosynthetic products.”

It is also found that while Elysia chlorotica stores plastids, the algal nuclei that are also sucked in do not survive. The team is yet to find out how the slug maintains the plastids and photosynthesis for months in absence of the nuclei, which are required to control their function.

The study has been published in the journal Molecular Biology and Evolution.

Source: Rutgers University–New Brunswick