PIERCE, S. K.*; MASSEY, S. E.; CURTIS, N. E.; Univ. of South Florida, Tampa; Univ. of South Florida, Tampa; Univ. of South Florida, Tampa: Horizontal transfer of functional genes between nuclear genomes of algae and sea slugs.

Gene transfer between prokaryotes or between endosymbiotic prokaryotes and their host cells has occurred many times. However, a similar transfer between multicellular species has never been demonstrated to date. During the past few years, we have presented some circumstantial and pharmacological evidence for the transfer of nuclear-encoded chloroplast genes between algae and sacoglossan sea slugs. Certain cells in the digestive epithelium of the slugs sequester chloroplasts from the algal food source and maintain them for substantial periods, utilizing photosynthetically produced substances from the endosymbiotic plastids as a nutritional source. Several plastid proteins are synthesized while the plastids reside in the slug cell. The synthesis of some of those proteins is blocked by cycloheximide indicating that their genes should be located in the nuclear genome of the slug. Now, we have evidence for the presence of the homolog of an algal nuclear gene, that codes for an endosymbiotic chloroplast protein (fucoxanthin-chlorophyll binding protein, FCP), in genomic DNA from a sea slug (Elysia crispata). In the slug cell, FCP is synthesized on cytosolic ribosomes and a probe for its gene binds to Southern blots of the slug genomic DNA. Therefore, we have found clear evidence of a gene that has been transferred between two multicellular species. Supported by NSF IBN 00315227