The plastid in apicomplexa: genome, function and evolution

Abstract

Protozoan parasites of the phylum apicomplexa (including Plasmodium and Toxoplasma) contain three types of genetic elements. These are nuclear, mitochondrial and 35 kb extrachromosomal DNA. The 35 kb DNA is present in a four membrane-bound organelle called the apicoplast, localized to a position adjacent to the apical end of the parasite nucleus. Sequence analysis of this 35 kb DNA has revealed extensive organizational similarity with chloroplast genomes. The conservation of the apicoplast across apicomplexa suggests that it plays a crucial role in parasite metabolism and apicoplast function has been linked with parasite survival. The presence of an organelle of prokaryotic origin in apicomplexan parasites has generated immense interest as investigators have explored its potential as a putative drug target for malaria and toxoplasmosis. In this review, we describe organizational features of the apicoplast genome, current understanding of its function(s) in the parasite and studies to trace its evolutionary origin.