The ghost plastid of Choreocolax polysiphoniae

Area of Science:

• Evolutionary Biology
• Phycology
• Genomics

Background:

• Parasitism is a widespread evolutionary strategy in eukaryotes, with over 100 independent origins in red algae.
• The prevailing model suggests red algal parasites evolve from closely related species, gradually infecting more distant hosts.
• Parasites typically integrate into host cells, utilizing host organelles and spreading via cell-to-cell connections.

Discussion:

• Microscopy and molecular data indicate red algal parasites often repurpose host plastids for dispersal, losing their own photosynthetic capabilities.
• The sequenced plastid genome of Choreocolax polysiphoniae (~90 kb) shows significant gene loss, including those for light harvesting and photosynthesis.
• This finding challenges the paradigm by demonstrating the presence of a native, albeit modified, plastid within the parasite.

Key Insights:

• The study presents the first plastid genome sequence from Choreocolax polysiphoniae, a red algal parasite.
• Choreocolax polysiphoniae possesses its own plastid, distinct from the host's, indicating alternative evolutionary routes to parasitism.
• The parasite's plastid has lost photosynthetic functions, highlighting adaptation to a non-photosynthetic lifestyle.

Outlook:

• Further genomic studies of red algal parasites are needed to understand the diversity of parasitic adaptations.
• Investigating the genetic mechanisms behind plastid acquisition and modification in parasites can reveal novel evolutionary strategies.
• Comparative genomics of parasite-host plastid pairs will illuminate the dynamics of organelle evolution and horizontal gene transfer.