Acquisition of photosynthetic chloroplasts from algae in the Elysia chlorotica

1. Acquisition of photosynthetic chloroplasts from algae in the Elysia chlorotica Olivia Archambault, John Minderman, Elizabeth Dudley, Mackenzie Tilley, and Russell Bowles

2. Horizontal Gene Transfer (HGT)

3. Rumpho M E et al. J Exp Biol 2011;214:303-311

4. Introduction • Species in certain phyla capture photosynthetic products through symbiotic relationships with cyanobacteria or algae • Consumed plastids are located intracellularly in the digest tract of the sea slug. • Certain species have evolved traits to help retain the plastids for longer periods. http://jeb.biologists.org/content/214/2/303.full#sec-2

5. Introduction • Results (Pierce et al 2012) suggest that algal nuclear genes are present in the sea slugs and that plastid protein and pigment turnover necessary to sustain powers of photosynthesis take place in the cells of E. chlorotica • Studies have been inconclusive about the presence of transferred genes from algae (you are not what you eat.) • If transferred at all, it is agreed that algal nuclear genes will be of a very low copy number.

6. Experiments • Several experiments were set out to see if E. Chlorotica receives genes from algae to become photosynthetic. • They explored whether nuclear gene transfer occurred, or just plastid transfer from the algae to E. Chlorotica. http://www.answers.com/topic/chloroplast

7. Results • The researchers (Pierce et al 2012) discovered that chloroplast encoded sequences were present in the RNA of the sea slugs.  • 101 chloroplast encoded protein coding genes matched sequences in the algae.   • 36 sequences which mapped to ribosomal protein subunits matched between slug and algal RNA and with chloroplast genome sequences.

8. Results • 88 out of 111 slug transcripts in the chloroplast encoded data sets were identical. • In order to prevent any contamination in the experiment, the researchers starved the slugs for 2 months to ensure that no algae was mistaken for E. Chlorotica matter. http://www.pbs.org/wgbh/nova/tech/algae-fuel.html

9. Discussion • Data (Pierce at el 2012) shows that the chloroplast genome is active within E. chlorotica cells and is producing transcripts for some chloroplast proteins. • Several transcripts found code for components of PSI and PSII reaction centers. • CytF and RuBisCO transcripts inside the slug show that the E. chlorotica synthesize these proteins

10. Multiple Hypotheses Several experiments, conducted by Pelletreau,Wa¨gele, and Pierce, respectively, hypothesized the following: • That a combination of unusual plastid stability, HGT, and long-term maintenance of cryptic algal products maintain the plastid cells. • That there is incredible plastid longevity, but no nuclear gene transfer, because in the feeding process no nuclear genes are transferred maintain the plastid cells. • That nuclear and chloroplast genes were transferred to produce plastids and proteins in the slug. http://wrtgfunfact.blogspot.com/2010/11/elysia-chlorotica-is-only-animal-known.html

11. Problems • In the first two experiments: • They assumed, there would be a large chloroplast transcript presence in the slug cells, as in plant cells, and would therefore be easy to identify. But this assumption is unproven and most likely false. • RNA taken was from slugs that did not go through photosynthesis and therefore most likely didn’t go through gene transfer to make plastids • The machines and techniques used only examined fraction of genes, and the database they compared it to didn’t have the algae the plastids most likely came from. • Both experiments make conclusions, either of which may still be correct, but neither have enough data to support their conclusion.

12. Conclusion • The first two experiments used PCR techniques, they returned a fewer number of genes, though more accurate, less genes were found to compare to. • Because of the size of the DNA and protein data sets, is it easy to find conclusion from limited data, but to prove the solution much more sequencing is required to prove anything. • Therefore no correct answer is present and the data is still inconclusive until more sequencing is done. http://www.epochtimes.com.ua/ru/science/theory-and-research/ny-zhyvotnoe-ny-rastenye-91954.html

13. Works citied • Wa¨gele H, Deusch O, Ha¨ndeler K, et al. (11 co authors). 2011. Transcriptomicevidence that longevity of acquired plastids in the photosynthetic slugs Elysia timida and Plakobranchusocellatusdoes not entail lateral transfer of algal nuclear genes. Mol BiolEvol. 28:699–706. • Mary E. Rumpho, Karen N. Pelletreau, Ahmed Moustafa, and Debashish Bhattacharya, 2011. The making of a photosynthetic animal. J. Exp. Biol. 214: 303-311. doi: 10.1242/​jeb.046540 • Pierce SK, Fang X, Schwartz JA, Jiang X, Zhao W, Curtis NE, Kocot KM, Yang B, Wang J. 2012. Transcriptomic evidence for the expression of horizontally transferred algal nuclear genes in the photosynthetic sea slug, Elysia chlorotica. Mol BiolEvol. 29(6):1545-56. Epub 2011 Dec 23. PubMed PMID: 22319135. doi: 10.1093/molbev/msr316