Reyes-Prieto, Adrian , Moustafa, Ahmed , Bhattacharya, Debashish .
Genome reduction and its effects on the plastid proteome.
The endosymbiosis that gave rise to the primary plastids of algae and plants left a major imprint on the nuclear genome of these photosynthetic eukaryotes. The proportion of genes transferred from the cyanobacterial endosymbiont to the nuclear genome has been estimated in Arabidopsis thaliana (18%, ca. 4,500) and in the glaucophyte alga Cyanophora paradoxa (ca. 11%, ca.1,500 genes). The striking difference between these values may be explained by repeated genome duplications that occurred during angiosperm evolution. Here we evaluated endosymbiotic gene transfer (EGT) in the free-living green algae Chlamydomonas reinhardtii (chlorophyceae, 15,114 predicted proteins) and the picoeukaryote Ostreococcus tauri (prasinophyte, 7,926 proteins). We were particularly interested in elucidating the effects of strong selection for overall genome reduction in Ostreococcus with regard to its effect on the ancestral set of plastid-targeted proteins of cyanobacterial origin. Specifically we asked the question, does the set of plastid-targeted proteins in Ostreococcus undergo an equivalent loss of genes as other functional groups or are these sequences “protected” due to their central function in this obligate photoautotroph? If gene loss does occur, then which plastid-targeted proteins are lost and what can we learn about plastid function from these data? To answer these questions, the set of Chlamydomonas (3,805) and Ostreococcus (2,347) predicted proteins that had a significant BLAST hit (E value <10-5) against any of 19 cyanobacterial genomes was subjected to phylogenomic analysis. This generated 2,983 and 1,785 bootstrapped distance trees in Chlamydomonas and Ostreococcus, respectively. After careful scrutiny, the unambiguous set of cyanobacterial genes was reduced to 479 in Chlamydomonas and ca. 294 in Ostreococcus. These preliminary data indicate that even though there is twice the number of predicted proteins Chlamydomonas as in Ostreococcus, the picoeukaryote retains ca. 61% of the cyanobacterial-derived proteins. These and other results will be discussed in the presentation
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1 - University of Iowa, Department of Biological Sciences and Roy J. Carver Center for Comparative Genomics, 446 Biology Building, Iowa City, Iowa, 52242, USA
Endosymbiotic Gene Transfer
Plastid targeted proteins
Presentation Type: Array
Location: Boulevard A/Hilton
Date: Wednesday, July 11th, 2007
Time: 4:00 PM