Cycad Coralloid Roots Contain Bacterial Communities Including Cyanobacteria and Caulobacter spp. That Encode...

Area of Science:

• Plant-microbe symbiosis
• Evolutionary biology
• Microbial ecology

Background:

• Cycads possess unique coralloid roots for nitrogen-fixing endophytic bacteria, representing an ancient symbiosis.
• Understanding the microbial composition and function within these roots is key to deciphering this relationship.

Purpose of the Study:

• To investigate the endophytic bacterial sub-communities in Dioon cycad coralloid roots.
• To provide evolutionary and functional insights into the ancient cycad-bacteria symbiosis.

Main Methods:

• Sub-community co-culture experiments to isolate predominant and rare bacteria.
• Phylogenomics and metabolic annotation for bacterial characterization.
• Shotgun metagenomics and whole-genome sequencing of cyanobacteria.

Main Results:

• Diazotrophic endophytes (Bradyrhizobium, Burkholderia, Mesorhizobium, Rhizobium, Nostoc) dominated.
• Genomes revealed two Dioon-specific cyanobacteria groups, suggesting co-evolution.
• Unique biosynthetic gene clusters for specialized metabolites, including peptides, were identified.
• Caulobacter species were found to co-exist with cyanobacteria, potentially interacting via a novel metabolite.

Conclusions:

• The cycad coralloid root harbors a specialized and phylogenetically structured endophytic community.
• Specialized metabolites play a significant role in mediating ancient symbiotic adaptations.
• This research offers an unprecedented view of the cycad root microbiome and its evolutionary significance.