Trypanosoma cruzi strains partition into two groups based on the structure and function of the spliced leader RNA and rRNA gene promoters

Abstract

We have previously identified a major proximal sequence element (PSE) responsible for transcription of the spliced leader (SL) gene from Trypanosama cruzi strain CL, and showed that the sequence encompassing this PSE exhibits ∼30% divergence between two major groups of T. cruzi isolates, but strong conservation within the groups. In this report, we show that the SL RNA gene promoter from the CL strain (group I) is efficiently expressed only in T. cruzi isolates from group I. Similarly, the sequence of the ∼643 bp promoter region of the T. cruzi rRNA is strongly conserved within, but diverged ∼20% between, the two groups. Reporter constructs driven by the rRNA promoter sequences from group I strains are strongly expressed after electroporation into other group I strains, but not expressed in group II strains. In contrast, constructs bearing rRNA promoter sequences from group II strains are active in strains from both groups. Phylogenetic analyses performed with both the rRNA and the SL RNA gene promoter sequences yielded similar trees, and these trees strongly reinforce the partitioning of known T. cruzi into two major groups that parallel the observed functional specificity of the promoters. Given the well-documented species specific pattern of both rRNA promoters and PSEs in higher eukaryotes, these results suggest an ancient evolutionary divergence among organisms currently classified as T. cruzi.