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Abstract Detail


Borrowed Chloroplasts: Secondary Endosymbiosis and the Chromalveolates

Bhattacharya, Debashish [1], Yoon, Hwan Su [2], Nosenko, Tetyana [3].

Endosymbiotic Gene Transfer and Plastid Origin in Chromalveolate Protists.

Endosymbiosis has spread photosynthesis to many branches of the eukaryotic tree of life however the history of photosynthetic organelle (plastid) gain and loss remains controversial. Fortuitously, endosymbiosis may leave a genomic footprint through the transfer of endosymbiont genes to the “host” nucleus (endosymbiotic gene transfer, EGT). EGT can be detected through comparison of host genomes to uncover the history of past plastid acquisitions. Here we focus on chromalveolates that are postulated to share a common red algal secondary endosymbiont. We used phylogenomics to analyze extensive expressed sequence tag (EST) and complete genome data from chromalveolates, red algae, plants, animals, fungi and bacteria to clarify the origin(s) of nuclear-encoded proteins that are targeted to the plastid to express their function. In one analysis of the haptophyte alga Emiliania huxleyi, we found 19 convincing case of EGT that did not contain significant paralogy and had strong bootstrap support at the internal nodes. Seventeen of these genes originated from the red algae, consistent with the chromalveolate hypothesis, whereas 2 genes were of green algal origin suggesting that other sources have contributed to plastid function in this group. In another analysis of the Florida “red tide” dinoflagellate Karenia brevis that has undergone tertiary plastid endosymbiosis, we identified 30 nuclear encoded plastid-targeted proteins that originated via EGT or horizontal gene transfer (HGT) from multiple different sources. We identified a fundamental divide between plant/red algal and chromalveolate plastid proteomes that reflects a history of mixotrophy in the latter group resulting in a highly chimeric proteome.


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1 - University of Iowa, Biology, Roy J. Carver Center for Comparative Genomics, 446 Biology Building, Iowa City, Iowa, 52242, USA
2 - Bigelow Laboratory for Ocean Sciences, 180 McKown Point Road, P.O. Box 475, West Boothbay Harbor, Maine, 04575, USA
3 - University of Iowa, Biology, Roy J. Carver Center for Comparative Genomics, 460 Biology Building, Iowa City, Iowa, 52242, USA

Keywords:
algae
chromalveolates
endosymbiosis
horizontal gene transfer
phylogenomics.

Presentation Type: Symposium or Colloquium Presentation
Session: SY15
Location: Waldorf Room/Hilton
Date: Wednesday, July 11th, 2007
Time: 11:00 AM
Number: SY15006
Abstract ID:1400


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