Evolutionary Patterns of Thylakoid Architecture in Cyanobacteria

Area of Science:

• Microbiology and Evolutionary Biology
• Cyanobacterial Ultrastructure and Phylogeny

Background:

• Thylakoid membrane spatial distribution in cyanobacteria is diverse but poorly understood across lineages.
• Thylakoid patterns have historically been used in cyanobacterial classification, but their evolutionary history needs updating with new data.

Purpose of the Study:

• To investigate the evolutionary history of thylakoid membrane arrangements in cyanobacteria.
• To correlate ultrastructural data with phylogenetic trees derived from rRNA and phylogenomic data.
• To reassess the taxonomic significance of thylakoid morphology.

Main Methods:

• Mapping ultrastructural data from over 200 cyanobacterial strains onto SSU rRNA gene trees.
• Comparison of the resulting phylogeny with a phylogenomic tree.
• Analysis of thylakoid arrangement patterns in relation to phylogenetic clades and cell size.

Main Results:

• Thylakoid architecture changes generally align with the phylogeny of housekeeping genes.
• Parietal arrangement is the ancestral state, with complex arrangements evolving in derived heterocytous cyanobacteria.
• Convergent evolution of radial and fascicular architectures is suggested; thylakoid arrangement is constrained by cell size (<2 μm).

Conclusions:

• Thylakoid morphology has limited taxonomic value, with only thylakoid absence and parallel arrangement being potentially informative apomorphies.
• Phylogenetic analyses reveal evidence of paraphyly and reversion to parietal patterns, alongside convergent evolution of other arrangements.
• Unknown (eco)physiological factors likely influence thylakoid patterns, and some proposed biogenesis factors may not be essential in all cyanobacteria.