MECHANISMS UNDERLYING THE EVOLUTION AND MAINTENANCE OF FUNCTIONALLY HETEROGENEOUS 18S RRNA GENES IN APICOMPLEXANS

Authors: Rooney, Alejandro - Alex

Submitted to: Molecular Biology and Evolution
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/21/2004
Publication Date: 9/1/2004
Citation: Rooney, A.P. 2004. Mechanisms underlying the evolution and maintenance of functionally heterogeneous 18S rRNA genes in Apicomplexans. Molecular Biology and Evolution. 21(9):1704-1711.

Interpretive Summary: This paper describes the results of a study on ribosomal RNA genes of agriculturally and biomedically important eukaryotic microbial pathogens. The study uncovered novel aspects of ribosomal RNA gene family evolution and carries significant impact for microbial genomics and gene family research. This study provides information on how ribosomal RNA gene families evolve and are organized at the genome level and will, therefore, aid scientists using ribosomal RNA genes to identify newly discovered microbes of agricultural, veterinary and human health significance.

Technical Abstract: In many species of Apicomplexa, the organization of ribosomal RNA (rRNA) genes deviates from the classic tandem array pattern that characterizes most eukaryotic species. For instance, rRNA genes in Plasmodium and Cryptosporidium are dispersed over different chromosomes and present in low copy number. Moreover, gene copies of the same species are often observed to differ substantially in terms of both sequence similarity and expression pattern. These observations are highly unusual in light of the widespread acceptance that rRNA genes evolve in a concerted manner in both eukaryotes and prokaryotes. As such, the aim of this study is to understand what processes underlie apicomplexan rRNA evolution by examining the 18S genes of various species. The results show that the genes of some species are divergent from one another and that some are highly conserved between species. These observations indicate that apicomplexan 18S rRNA genes evolve according to a birth-and-death model under strong purifying selection. In addition to their importance in the study of protist biology and evolution, the broader scale implications of these findings for multigene family evolution and evolutionary genomics in general are also discussed.