Seed-free Plants at the Genomic Scale
Burns, John , Paasch, Amber , Narechania, Apurva , Kim, Eunsoo .
Food vs. photons: The genomics of a green alga that eats bacteria.
Ingestion of a photosynthetic bacterium was a key step in plastid genesis and the evolution of photosynthetic eukaryotes. The ancestor to Chloroplastida (green algae and land plants) is presumed to be bacterivorous. A major phenotypic transition occurred in this lineage from heterotrophy to mixotrophy to autotrophy. Yet, almost all extant members of Chloroplastida are solely photo-autotrophic. Recently, however, Cymbomonas tetramitiformis, a prasinophyte green alga, was definitively confirmed to ingest bacteria into a large, permanent vacuole while also conducting photosynthesis. Since then, two additional prasinophytes have been found to ingest fluorescently-tagged bacteria. Cymbomonas has phenotypic characteristics in common with the hypothetical pre-photosynthetic ancestor and serves as a model to study plastid acquisition. We sequenced the Cymbomonas genome and performed comparative analyses to determine the influence of nutritional mode on a genome. We found a clear distinction between obligate heterotrophs, autotrophs and mixotrophs, like Cymbomonas. Cymbomonas harbors genes related to feeding that tend to be missing in obligate autotrophs, and it harbors genes related to small molecule biosynthesis (i.e. amino acids) that tend to be missing in obligate heterotrophs. These results suggest that feeding facilitates gene loss in biosynthetic pathways. Over time, the accumulation of missing biosynthetic pathways in heterotrophs may impede newer lineages, such as metazoans, amoebozoans and ciliates, from becoming autotrophic after acquiring a photosynthetic endosymbiont.
1 - American Museum of Natural History, Invertebrate Zoology, 79th St. at Central Park West, New York, NY, 10024, USA
Presentation Type: Colloquium Presentations
Candidate for Awards:None