lateral gene transfer from alga to sea slug

[eub]

Did you know that when sea slugs acquire the photosynthetic capability of algae they eat, they're only keeping the chloroplasts? And apparently it's puzzling that this works, because they shouldn't be able to operate without algal nuclear proteins.

http://www.pnas.org/content/105/46/17867

Two possible explanations for the persistence of photosynthesis in the sea slug are (i) the ability of V. litorea plastids to retain genetic autonomy and/or (ii) more likely, the mollusc provides the essential plastid proteins. Under the latter scenario, genes supporting photosynthesis have been acquired by the animal via horizontal gene transfer and the encoded proteins are retargeted to the plastid. We sequenced the plastid genome and confirmed that it lacks the full complement of genes required for photosynthesis. In support of the second scenario, we demonstrated that a nuclear gene of oxygenic photosynthesis, psbO, is expressed in the sea slug and has integrated into the germline.

1) I wonder how much it would take for the sea slug to make its own chloroplasts too. Maybe a lot of basic dependencies get pulled in, I suppose.

2) How heavyweight is the genetic package that lets the sea slug do what it does? Can I have a copy?

Comments

[aquaeri.livejournal.com]

1) Plants don't make their own chloroplasts - chloroplasts are independent organelles, ultimately descended from free-living bacteria (probably related to cyanobacteria) - and they have their own genomes and divide within each cell. The sea slug, by having the nuclear genes required (which have been gradually co-opted by plants as a way of holding the chloroplasts "hostage") is well on the way to having its own - the sea slug just needs chloroplasts in its germ line cells so each new sea slug has chloroplasts on hand in each cell, like plants do it. (And like we do with mitochondria, which are also formerly free-living bacteria 'taken hostage'.)

[eub.livejournal.com]

Is it known whether the slug's chloroplasts are reproducing at all? If not, the slug may be lacking some algal nuclear genes involved in that process?

I don't know, but I can imagine that the expression of signals for chloroplast reproduction would have to be done carefully, wired in to the host cell's growth controls, so the plastids don't overgrow or undergrow the host...

[aquaeri.livejournal.com]

I can't read the entire paper, but I'd guess from the wording of the abstract that they don't reproduce, just survive long enough to make themselves useful. And yes, there's probably another batch of nuclear genes the sea slugs will need to regulate chloroplast growth and division. So the way they're doing it, by stealing chloroplasts from the algae they're eating anyway, seems like a good solution.

Also, green sea slugs! yay! (Why am I not remotely surprised that "Sea Slug Forum" is hosted by an Australian museum?)