Eukaryotic algal phytochromes span the visible spectrum.

Area of Science:

• Plant biology
• Photoreception
• Aquatic photosynthesis

Background:

• Phytochromes are plant photoreceptors that regulate responses to red and far-red light.
• In aquatic environments, light spectrum changes with depth, necessitating adaptation for photosynthesis.
• Phytochrome-related proteins are present in algae, despite the different light conditions.

Purpose of the Study:

• To investigate the photosensory properties of phytochromes from diverse algal species.
• To determine if algal phytochromes have adapted to sense different light wavelengths beyond red/far-red.
• To understand the spectral tuning of phytochromes in aquatic photosynthetic eukaryotes.

Main Methods:

• Examined seven phytochromes from prasinophyte, heterokont, and glaucophyte algae.
• Utilized circular dichroism (CD) spectroscopy to characterize photosensory properties.
• Analyzed chromophore structure in the far-red-absorbing photostate.

Main Results:

• Algal phytochromes exhibit diverse spectral tuning, sensing beyond red/far-red light.
• Specific phytochromes were found to detect orange, green, and blue light.
• CD spectroscopy indicated a structurally heterogeneous chromophore in the far-red-absorbing state.

Conclusions:

• Phytochromes in aquatic photosynthetic eukaryotes have evolved extensive spectral tuning.
• This spectral adaptation allows algae to utilize available light wavelengths in aquatic environments.
• Diverse algal lineages show independent evolution of novel phytochrome photosensory capabilities.