Controllable phycobilin modification: an alternative photoacclimation response in cryptophyte algae

Abstract

Cryptophyte algae are well known for their ability to survive under low light conditions through the use of their auxiliary light harvesting antennas, phycobiliproteins. Mainly acting to absorb light where chlorophyll cannot (500-650 nm), phycobiliproteins also play an instrumental role in helping cryptophyte algae respond to changes in light intensity through the process of photoacclimation. Until recently, photoacclimation in cryptophyte algae was only observed as a change in the cellular concentration of phycobiliproteins; however, an additional photoacclimation response was recently discovered that causes shifts in the phycobiliprotein absorbance peaks following growth under red, blue, or green light. Here, we reproduce this newly identified photoacclimation response in two other species of cryptophyte algae, P. sulcata and H. pacifica, and elucidate the origin of the response on the protein level. We compare isolated native and photoacclimated phycobiliproteins for these two species using spectroscopy and mass spectrometry, and we report the x-ray structures of the PC577 light harvesting complex and corresponding photoacclimated complex. We find that neither the protein sequences, nor the protein structures are modified by photoacclimation. We conclude that cryptophyte algae change a chromophore in one site of their phycobiliprotein beta-subunits as part of the photoacclimation response to changes in the spectral quality of light. Ultrafast pump-probe spectroscopy shows that the energy transfer is weakly affected by the photoacclimation.

Cascading effects of prey identity on gene expression in a kleptoplastidic ciliate

“…Orthologous genes vary wildly in the four cryptophyte species, with the highest number of shared genes in RS and SM (90%) and the fewest shared genes between R. salina and H. pacifica (38%). Additionally, plastid metabolism varies dramatically among these cryptophyte species, particularly between red and blue‐green lineages with greater evolutionary distance (Cunningham et al, 2019 ; Greenwold et al, 2019 ; Spangler et al, 2021 ) including different phycobiliproteins–accessory pigments that facilitate efficient light harvesting in coastal environments. Phycobiliproteins are tuned to different light wavelengths and intensities in cryptophytes that contain either phycoerythrin (red, Cr‐PE) or phycocyanin (blue‐green, Cr‐PC).…”

“…Phycobiliproteins are tuned to different light wavelengths and intensities in cryptophytes that contain either phycoerythrin (red, Cr‐PE) or phycocyanin (blue‐green, Cr‐PC). R. salina and S. major are red pigmented and have phycoerythrin (CR‐PE 545), while H. pacifica and Chroomonas mesostigmatica are blue‐green pigmented and contain phycocyanin (primarily Cr‐PC577 HP Cr‐PC645 CM; Cunningham et al, 2019 ; Moestrup et al, 2012 ; Spangler et al, 2021 ). In addition to photosynthetic output and nutritional support from the host, a high degree of variation in fatty acid composition and daily production has been shown for several of the cryptophytes used in this study (Peltomaa et al, 2017 ).…”