How Really Ancient Is Paulinella Chromatophora?

Area of Science:

• Marine biology
• Evolutionary biology
• Microbial genomics

Background:

• Paulinella chromatophora harbors a cyanobacterial endosymbiont, forming a 'plastid in the making' through a secondary primary endosymbiosis.
• Previous estimations of the chromatophore's age, based on pseudogene disintegration in Buchnera aphidicola, suggested a minimum age of 60 million years.

Purpose of the Study:

• To re-evaluate the age of the chromatophore in Paulinella chromatophora using molecular clock methods.
• To establish a more precise timeline for the secondary primary endosymbiosis event.

Main Methods:

• Analysis of the 18S rRNA gene sequence from Paulinella chromatophora.
• Application of a lognormal relaxed molecular clock model for divergence time estimation.
• Calibration of the molecular clock using established paleontological or molecular data.

Main Results:

• Molecular clock analysis estimates the divergence of Paulinella chromatophora from heterotrophic relatives between 90 and 140 million years ago.
• This age range provides a maximum age for the origin of the cyanobacterial endosymbiont (chromatophore).

Conclusions:

• The origin of the chromatophore in Paulinella chromatophora is significantly older than previously estimated.
• This study provides a refined timescale for a key event in plastid evolution and endosymbiosis.