Journal of Phycology: Vol. 44 pp. 2-6
Phylogenomics and secondary plastids: A look back and a look ahead
Edward L. Braun* and Naomi Phillips
Department of Zoology, University of Florida, Gainesville, Florida 32611, USA (E.L.B.); Biology Department, Arcadia University, 450 S. Easton Rd., Glenside, Pennsylvania 19038, USA (N.P.)
Despite their importance to evolution, ecology, and cell biology, eukaryotes that acquired plastids through secondary endosymbiosis remain poorly studied from a genomic standpoint. Chromalveolata, a eukaryotic supergroup proposed to have descended from a heterotrophic eukaryote that acquired a red algal plastid by secondary endosymbiosis, includes four major lineages (alveolates, cryptophytes, haptophytes, and heterokonts). The chromalveolates exhibit remarkable diversity of cellular organization, and the available data suggest that they exhibit equal diversity in their genome organization. One of the most obvious differences in cellular organization is the retention of a highly reduced red algal nucleus in cryptophytes (also known as cryptomonads), but there are other major differences among chromalveolate lineages, including the loss of photosynthesis in multiple lineages. Although the hypothesis of chromalveolate monophyly is appealing, there is limited support for the hypothesis from nuclear genes, and questions have even been raised about the monophyly of chromalveolate plastids. Evidence for the chromalveolate hypothesis from large-scale nuclear data sets is reviewed, and alternative hypotheses are described. The potential for integrating information from chromalveolate genomics into functional genomics is described, emphasizing both the methodological challenges and the opportunities for future phylogenomic analyses of these groups.
This manuscript is one of six papers written to summarize presentations given as part of a symposium at the Botany and Plant Sciences Joint Congress, July 7–11, 2007, in Chicago, IL that was entitled “Borrowed Chloroplasts: Secondary Endosymbiosis and the Chromalveolates.” The symposium was organized by N.P., Debashish Bhattacharya (University of Iowa), and E.L.B. and it was funded in part by the National Science Foundation and the Botanical Society of America.
* Corresponding author