A plastid without a genome: evidence from the nonphotosynthetic green algal genus Polytomella

Plant Physiol. 2014 Apr;164(4):1812-9. doi: 10.1104/pp.113.233718. Epub 2014 Feb 21.

Abstract

Polytomella spp. are free-living, nonphotosynthetic green algae closely related to the model organism Chlamydomonas reinhardtii. Although colorless, Polytomella spp. have a plastid, but it is still unknown whether they harbor a plastid genome. We took a next generation sequencing approach, along with transcriptome sequencing, to search for a plastid genome and an associated gene expression system in Polytomella spp. Illumina sequencing of total DNA from four Polytomella spp. did not produce any recognizable plastid-derived reads but did generate a large number of mitochondrial DNA sequences. Transcriptomic analysis of Polytomella parva uncovered hundreds of putative nuclear-encoded, plastid-targeted proteins, which support the presence of plastid-based metabolic functions, similar to those observed in the plastids of other nonphotosynthetic algae. Conspicuously absent, however, were any plastid-targeted proteins involved in the expression, replication, or repair of plastid DNA. Based on these findings and earlier findings, we argue that the Polytomella genus represents the first well-supported example, to our knowledge, of a primary plastid-bearing lineage without a plastid genome.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Cell Nucleus / genetics
  • Chlorophyta / genetics*
  • DNA, Plant / genetics
  • Gene Expression Regulation, Plant
  • Genes, Plant
  • Genome, Mitochondrial / genetics
  • Genome, Plastid / genetics*
  • Photosynthesis / genetics*
  • Phylogeny
  • Plastids / genetics*
  • Sequence Analysis, DNA

Substances

  • DNA, Plant