Convergent extreme reductive evolution in ancient planthopper symbioses

Area of Science:

• Microbiology
• Evolutionary Biology
• Genomics

Background:

• Heritable endosymbiotic bacteria provide essential nutrients to sap-sucking insects.
• These bacteria typically possess highly reduced and conserved genomes.
• Co-evolution with hosts over millions of years shapes bacterial genome reduction.

Purpose of the Study:

• Investigate genomic changes in planthopper endosymbionts Sulcia and Vidania.
• Understand the impact of co-infections and host ecological shifts on genome reduction.
• Characterize the smallest known bacterial genomes and their implications for symbiont evolution.

Main Methods:

• Comparative genomics of Sulcia and Vidania endosymbionts.
• Analysis of bacterial genome size and gene content.
• Phylogenetic analysis to trace evolutionary history.
• Investigation of environmental and co-infection factors influencing genome evolution.

Main Results:

• Identified extremely reduced bacterial genomes (50-52kb) in Vidania endosymbionts.
• Observed convergent evolution of minuscule genomes in different planthopper lineages.
• Highlighted similarities in gene content, including phenylalanine biosynthesis, in convergent genomes.
• Demonstrated that host ecological switches and co-infections accelerate genome reduction.

Conclusions:

• Endosymbiont genome reduction is influenced by host factors beyond simple co-diversification.
• Extreme genome reduction approaches the dependency level of organelles.
• The bacteria-organelle boundary is further blurred by extreme genomic streamlining in symbionts.