Transcriptome analysis of the short-term photosynthetic sea slug <i>Placida dendritica</i>

doi:2015.30.4.303

Algae > Volume 30(4); 2015 > Article

Algae 2015;30(4): 303-312. doi: https://doi.org/10.4490/algae.2015.30.4.303

Transcriptome analysis of the short-term photosynthetic sea slug Placida dendritica

Ji Hee Han¹, Tatyana A. Klochkova¹, Jong Won Han², Junbo Shim³ and Gwang Hoon Kim¹^,*

¹Department of Biology, Kongju National University, Kongju 32588, Korea
²National Marine Biodiversity Institute of Korea, Seocheon 33662, Korea
³Seaweed Research Center, National Fisheries Research & Development Institute, Mokpo 58746, Korea

*Corresponding Author

Email: ghkim@kongju.ac.kr

ABSTRACT

The intimate physical interaction between food algae and sacoglossan sea slug is a pertinent system to test the theory that “you are what you eat.” Some sacoglossan mollusks ingest and maintain chloroplasts that they acquire from the algae for photosynthesis. The basis of photosynthesis maintenance in these sea slugs was often explained by extensive horizontal gene transfer (HGT) from the food algae to the animal nucleus. Two large-scale expressed sequence tags databases of the green alga Bryopsis plumosa and sea slug Placida dendritica were established using 454 pyrosequencing. Comparison of the transcriptomes showed no possible case of putative HGT, except an actin gene from P. dendritica, designated as PdActin04, which showed 98.9% identity in DNA sequence with the complementary gene from B. plumosa, BpActin03. Highly conserved homologues of this actin gene were found from related green algae, but not in other photosynthetic sea slugs. Phylogenetic analysis showed incongruence between the gene and known organismal phylogenies of the two species. Our data suggest that HGT is not the primary reason underlying the maintenance of short-term kleptoplastidy in Placida dendritica.

Key words: actin; Bryopsis plumosa; horizontal gene transfer; kleptoplastidy; Placida dendritica; transcriptome