Intragenomic sequence variations in the second internal transcribed spacer (ITS2) ribosomal DNA of the malaria vector Anopheles stephensi

PLoS One. 2021 Jun 14;16(6):e0253173. doi: 10.1371/journal.pone.0253173. eCollection 2021.

Abstract

Second Internal Transcribed Spacer (ITS2) ribosomal DNA (rDNA) sequence is a widely used molecular marker for species-identification or -delimitation due to observed concerted evolution which is believed to homogenize rDNA copies in an interbreeding population. However, intra-specific differences in ITS2 of Anopheles stephensi have been reported. This study reports the presence of intragenomic sequence variation in the ITS2-rDNA of An. stephensi and hypothesizes that observed intra-specific differences in this species may have resulted due to ambiguous DNA sequence-chromatogram resulting from intragenomic heterogeneity. Anopheles stephensi collected from different parts of India were sequenced for complete ITS2 and the variable region of 28S-rDNA (d1-d3 domains). Intragenomic variations were found in ITS2 region of all An. stephensi sequenced, but no such variation was observed in d1 to d3 domains of 28S-rDNA. Cloning and sequencing of ITS2 through the d3 domain of the 28S region of rDNA from representative samples from northern, central, and southern India confirmed the presence of intragenomic variation in ITS2 due to transitions at three loci and two bp indel in a di-nucleotide microsatellite locus. Multiple haplotypes were observed in ITS2 raised from such variations. Due to the absence of detectable intragenomic sequence variation in the d1 to d3 domain of 28S rDNA of An. stephensi, this region can serve as an ideal reference sequence for taxonomic and phylogenetic studies. The presence of intragenomic variation in rDNA should be carefully examined before using this as a molecular marker for species delimitation or phylogenetic analyses.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Anopheles / genetics*
  • Anopheles / pathogenicity
  • DNA, Ribosomal / genetics
  • DNA, Ribosomal Spacer / genetics*
  • Genetic Variation / genetics
  • Genome, Insect / genetics*
  • Haplotypes / genetics
  • Humans
  • India / epidemiology
  • Malaria / epidemiology
  • Malaria / genetics*
  • Malaria / parasitology
  • Malaria / transmission
  • Mosquito Vectors / genetics
  • Mosquito Vectors / parasitology
  • Phylogeny

Substances

  • DNA, Ribosomal
  • DNA, Ribosomal Spacer

Grants and funding

This research was supported by the Department of Science & Technology, India, https://dst.gov.in/ (OPS) and ICMR-Senior Research Fellowship (SM and GS). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.