Plant & Animal Genomes XIII Conference

January 15-19, 2005
Town & Country Convention Center
San Diego, CA

EST Genomics Of The Dinoflagellate Alexandrium tamarense.

Jeremiah D Hackett¹ , M. Bento Soares² , Thomas L. Casavant³ , Debashish Bhattacharya¹

¹  University of Iowa, Department of Biological Sciences and Center for Comparative Genomics, 315 Biology Building, Iowa City, IA, 52242

²  University of Iowa, Department of Pediatrics, 4184 MERF, Iowa City, IA 52242

³  University of Iowa, Department of Electrical and Computer Engineering,5316 SC, Iowa City, IA, 52242

Dinoflagellate algae are important primary producers and of significant ecological and economic impact because of their ability to form "red tides". They are also models for evolutionary research because of an unparalleled ability to capture photosynthetic organelles (plastids) through endosymbiosis. The location and extent of the plastid genome in the dominant perdinin-containin dinoflagellates remain, however, two of the most intriguing issues in plastid evolution. The plastid genome in these taxa is reduced to single-gene minicircles encoding an incomplete (until now 15) set of plastid proteins. The location of the remaining photosynthetic genes is unknown. We generated a data set of 6,723 unique expressed sequence tags (ESTs) from the toxic dinoflagellate Alexandrium tamarense to find the missing plastid genes and to understand the impact of endosymbiosis on genome evolution. We identified 48 of the non-minicircle-encoded photosynthetic genes in the nuclear genome of A. tamarense, accounting for the majority of the photosystem. Fifteen genes that are always found on the plastid genome of other algae and plants have been transferred to the nucleus in A. tamarense. The plastid-targeted genes have red and green algal origins. These results highlight the unique position of dinoflagellates as the champions of plastid gene transfer among photosynthetic eukaryotes. Dinoflagellates are also known for their unique nuclear cell biology. Their nuclear genome is comprised of chromosomes that lack histones and it is believed that these proteins were lost in this lineage. We have, however, identified a nuclear encoded histone H2A.X in our EST dataset, indicating that A. tamarense maintains at least one histone. This histone may have been maintained for its role in double-stranded DNA break repair.