Low-light-adapted Prochlorococcus species possess specific antennae for each photosystem

Area of Science:

• Marine microbiology
• Photosynthesis research
• Genomics and adaptation

Background:

• Prochlorococcus is the most abundant photosynthetic organism globally.
• Its wide oceanic depth distribution is linked to distinct genotypes adapted to low- or high-light environments.
• The pcb genes, crucial for light-harvesting antenna proteins, show varied copy numbers between low- and high-light strains, but the reason is unclear.

Purpose of the Study:

• To investigate the genetic basis for Prochlorococcus' adaptation to different light environments.
• To understand the role of pcb gene copy number and regulation in light-harvesting antenna protein diversity.
• To compare light-harvesting strategies in Prochlorococcus with those in other photosynthetic organisms.

Main Methods:

• Comparative genomic analysis of pcb genes in different Prochlorococcus strains (MIT 9313, SS120, MED4).
• Identification of pcb gene expression patterns under varying light and iron conditions.
• Functional annotation of pcb genes in relation to Photosystem I (PSI) and Photosystem II (PSII).

Main Results:

• The low-light adapted strain MIT 9313 possesses an iron-stress-induced pcb gene for PSI and a constitutive pcb gene for PSII.
• The very low-light adapted strain SS120 exhibits seven pcb genes for constitutive PSI/PSII antennae and one PSI iron-regulated gene.
• The high-light adapted strain MED4 has only a single constitutive PSII antenna pcb gene.

Conclusions:

• Adaptation to low-light conditions in Prochlorococcus involves multiplication and specialization of pcb genes, similar to plant and algal light-harvesting protein evolution.
• Differential regulation and copy number variation of pcb genes are key mechanisms for niche adaptation in Prochlorococcus.
• This genetic plasticity allows Prochlorococcus to thrive across a wide range of oceanic light environments.