Differing isoforms of the cobalamin binding photoreceptor AerR oppositely regulate photosystem expression

Area of Science:

• Microbiology
• Photochemistry
• Molecular Biology

Background:

• Phototrophic microorganisms regulate photosystem synthesis in response to light.
• Purple photosynthetic bacteria utilize cobalamin (B12) as a blue-light chromophore in the novel photoreceptor AerR.
• AerR interacts with the transcription factor CrtJ to modulate photosystem gene expression.

Purpose of the Study:

• To investigate the isoforms of the AerR photoreceptor in purple photosynthetic bacteria.
• To determine how light and growth phase affect AerR isoform production and function.
• To elucidate the regulatory roles of different AerR isoforms on photosystem synthesis and other cellular processes.

Main Methods:

• Analysis of AerR protein translation and isoform production.
• Pigmentation assays to assess photosystem synthesis.
• Transcriptomic analysis to evaluate gene expression changes.

Main Results:

• AerR is translated into two isoforms differing by 41 amino acids at the N-terminus.
• The ratio of long to short AerR isoforms is influenced by light intensity and growth phase.
• The short AerR isoform represses photosynthesis genes, while the long isoform activates them.
• The long AerR isoform also upregulates genes involved in cellular metabolism and motility.

Conclusions:

• AerR isoform regulation provides a sophisticated mechanism for controlling photosystem synthesis in response to environmental cues.
• The differential functions of AerR isoforms highlight a complex regulatory network impacting not only photosynthesis but also broader cellular functions.
• This study reveals a novel light-dependent regulatory mechanism involving cobalamin-based photoreceptors and protein isoforms in bacteria.