International Society of Protistologists 57 th Annual Meeting 20 – 24 June 2006 Lisbon , Portugal ( 80 A – 175 A ) 80

Protist genomes: a strange brew of broken rules. P. KEELING, Department of Botany, University of British, Columbia, Vancouver, BC, Canada. By nearly all criteria, protists make up the great majority of eukaryotic diversity. This is well illustrated at the level of the genome, where protists have broken just about every rule we think we know about genome form, content, and function. I will examine some ‘‘extreme’’ genomes studied in my lab, and what these deviants can tell us about genome evolution. Some of the most unusual nuclear genomes we know about are found in microsporidian intracellular parasites and the algal endosymbionts called nucleomorphs in cryptomonads and chlorarachniophytes. In both cases genomes have been highly reduced by gene loss and by compacting the remaining genes into a tighter space. Both processes have had significant impacts, most obviously on form but also on function. These processes are frequently studied in the most extreme of these genomes (i.e. the smallest ones), but the nature of their less compacted relatives is also of interest as they can tell us how these genomes got to be the way they are and whether this trajectory is reversible. In contrast to the highly compacted genomes, other groups (notably dinoflagellates) have extremely large genomes, and once again these appear to be linked to massive but poorly understood changes in how the genome works. In terms of genome content, one of the most radical affects on a genome can come about through endosymbiosis. The merger of two cells involves the merger of many genomes: in some cases as many as six genomes and in some dinoflagellates the historical footprint of as many as 10, come together to make up one cell. While endosymbiosis is a catastrophic example of changes in genome content, the gradualist process of lateral gene transfer may be no less important. Indeed, as the gene complement of protist genomes is studied in more detail, they are emerging as models for how genes can flow between distantly related species one (or a few) at a time. The impacts of many small transfers may even be greater than the impacts of massive transfers associated with endosymbiosis.