Abstract
We observed differences in lhc classification in Chromista. We proposed a classification of the lhcf family with two groups specific to haptophytes, one specific to diatoms, and one specific to seaweeds. Identification and characterization of the Fucoxanthin and Chlorophyll a/c-binding Protein (FCP) of the haptophyte microalgae Tisochrysis lutea were performed by similarity analysis. The FCP family contains 52 lhc genes in T. lutea. FCP pigment binding site candidates were characterized on Lhcf protein monomers of T. lutea, which possesses at least nine chlorophylls and five fucoxanthin molecules, on average, per monomer. The expression of T. lutea lhc genes was assessed during turbidostat and chemostat experiments, one with constant light (CL) and changing nitrogen phases, the second with a 12 h:12 h sinusoidal photoperiod and changing nitrogen phases. RNA-seq analysis revealed a dynamic decrease in the expression of lhc genes with nitrogen depletion. We observed that T. lutea lhcx2 was only expressed at night, suggesting that its role is to protect \\cells from return of light after prolonged darkness exposure.
Highlights
Marine planktonic photosynthetic organisms are responsible for approximately 50% of Earth’s primary production and fuel the global ocean biological carbon pump (Field et al, 1998)
In two diatoms (Fragilariopsis cylindrus and Thalassiosira pseudonana) and one haptophyte (Emiliania huxleyi), sequences are classified as light-harvesting complexes (LHCs) proteins (i.e., Fucoxanthin and Chlorophyll a/c-binding Protein (FCP))
These results lead us to study the FCP proteins of the FCP complex in T. lutea coded by the lhcf, lhcr, and lhcx genes
Summary
Marine planktonic photosynthetic organisms are responsible for approximately 50% of Earth’s primary production and fuel the global ocean biological carbon pump (Field et al, 1998). Among these producers, 50% are represented by Chromista (Cavalier-Smith, 2004), including haptophytes, which are abundant primary producers. Haptophytes are ubiquitous, and they play an important role in ocean carbon fluxes (Jordan and Chamberlain, 1997; Green and Jordan, 2000; Liu et al, 2009; Edvardsen et al, 2016). In Chromista, light-harvesting complexes (LHCs) are composed of pigments and fucoxanthin chlorophyll a/cbinding proteins (FCPs). The spatial organization of FCPs and their carotenoids confer to Chromista a very strong absorption capacity in the blue-green spectral range of visible light, which are the most available radiations in the water column (Wang et al, 2019a,b)
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