Blue–red chromatic acclimation in the red alga Pyropia yezoensis

Abstract

Phycobilisomes, light-harvesting complexes present in cyanobacteria, red algae and glaucophyte algae, can absorb a wide range of light wavelengths to optimize photosynthetic efficiency. In certain cyanobacteria, phycobilisomes are remodeled via reversible changes in their complement of phycobiliproteins, including phycoerythrin (PE) and phycocyanin (PC), in response to green light (GL) and red light (RL) irradiation, a phenomenon termed chromatic acclimation (CA). Here, we investigated whether changes in light wavelength similarly modify the composition of phycobilisomes in the red alga Pyropia yezoensis. We observed that when P. yezoensis thalli were irradiated with blue light (BL) and RL, their color became brilliant red and green due to increased levels of PE and PC, respectively. Notably, these color changes in thalli were reversible. Although GL also increased the PC content, its effect was weaker than that of RL, resulting in brown thalli. Thus, we conclude that P. yezoensis remodels phycobilisomes mainly in response to BL and RL, reflecting a blue–red CA, which has not been reported in cyanobacteria. Discovery of this novel type of CA in eukaryotic P. yezoensis provides insight into regulatory mechanisms for fine-tuning photosynthetic pigment contents in phycobilisomes of photosynthetic organisms.