Abstract
Diatoms greatly contribute to carbon fixation and thus strongly influence the global biogeochemical balance. Capable of chromatic acclimation (CA) to unfavourable light conditions, diatoms often dominate benthic ecosystems in addition to their planktonic lifestyle. Although CA has been studied at the molecular level, our understanding of this phenomenon remains incomplete. Here we provide new data to better explain the acclimation-associated changes under red-enhanced ambient light (RL) in diatom Phaeodactylum tricornutum, known to express a red-shifted antenna complex (F710). The complex was found to be an oligomer of a single polypeptide, Lhcf15. The steady-state spectroscopic properties of the oligomer were also studied. The oligomeric assembly of the Lhcf15 subunits is required for the complex to exhibit a red-shifted absorption. The presence of the red antenna in RL culture coincides with the development of a rounded phenotype of the diatom cell. A model summarizing the modulation of the photosynthetic apparatus during the acclimation response to light of different spectral quality is proposed. Our study suggests that toggling between alternative organizations of photosynthetic apparatus and distinct cell morphologies underlies the remarkable acclimation capacity of diatoms.
Highlights
Widespread and diverse diatoms represent an ecologically important group of primary producers among heterokont algae[1,2,3,4]
The light-harvesting apparatus of the model diatom Phaeodactylum (P.) tricornutum, comprises several groups of light-harvesting proteins[23]: i) a set of Lhcr proteins that form the antenna of the photosystem I (PSI), coded for by 14 genes; ii) 4 stress-related Lhcx proteins; and iii) the largest group of 17 Lhcf proteins that includes the principal light-harvesting complex (LHC) of diatoms, the fucoxanthin chlorophyll a/c–binding proteins (FCPs)
One intriguing aspect of chromatic acclimation (CA) is a formation of red-shifted forms of chlorophyll (Chl) a induced in the algal cultures grown under red-enhanced illumination[24,25]
Summary
Widespread and diverse diatoms represent an ecologically important group of primary producers among heterokont algae[1,2,3,4]. Marine diatoms are found both (i) free-living in the open ocean as a prominent component of phytoplankton, and (ii) biofilm-forming in benthic habitats such as coastal waters, estuaries and rock pools[5,6] Their global abundance depends on a strong ability to adapt to the changing environment including variation of light intensity and spectral quality along the water column[7,8,9,10,11,12]. Response of photosynthetic organisms to changes in the spectral composition of the ambient radiation was discussed under the terms of chromatic adaptation theory as early as in the 1800’s by Engelman[13]. For the first time, a precise analysis of its protein composition, steady state spectroscopic properties at room temperature and the oligomeric state was achieved
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