Transient molecular chimerism for exploiting xenogeneic organelles

Area of Science:

• Cell Biology
• Evolutionary Biology
• Biochemistry

Background:

• Organelle genomes confirm prokaryotic ancestry, but most organelle proteins are nuclear-encoded, creating molecular chimerism.
• The evolutionary drivers of this chimerism remain poorly understood, lacking substantial empirical evidence.

Purpose of the Study:

• To provide biochemical evidence for transient molecular chimerism in nature.
• To elucidate a potential mechanism for chimerism.
• To investigate the role of nuclear-encoded proteins in supporting photosynthesis within transient kleptoplasts.

Main Methods:

• Focusing on two kleptoplast-targeted proteins in Rapaza viridis: RuBisCO small subunit-like protein (RvRbcS-like) and RuBisCO activase homologue.
• Utilizing immunofluorescence microscopy to confirm protein localization.
• Employing knockdown and knockout experiments to assess functional impact on photosynthesis.

Main Results:

• Confirmed kleptoplast localization of RvRbcS-like and RuBisCO activase.
• Demonstrated impaired photosynthesis upon knockdown/knockout, especially for RvRbcS-like.
• Identified a unique carboxyl-terminal extension in RvRbcS-like, suggesting a role in pyrenoid reorganization and kleptoplast remodeling.

Conclusions:

• Rapaza viridis exhibits transient molecular chimerism, with nuclear proteins supporting photosynthesis in xenogeneic kleptoplasts.
• Protein translocation into kleptoplasts involves rapid, de novo assembly of transport systems after each acquisition.
• This organism serves as a valuable model for studying organelle origins and evolution.