The Fucoxanthin Chlorophyll a/c-Binding Protein in Tisochrysis lutea: Influence of Nitrogen and Light on Fucoxanthin and Chlorophyll a/c-Binding Protein Gene Expression and Fucoxanthin Synthesis

Abstract

We observed differences in <i>lhc</i> classification in Chromista. We proposed a classification of the <i>lhcf</i> family with two groups specific to haptophytes, one specific to diatoms, and one specific to seaweeds. Identification and characterization of the Fucoxanthin and Chlorophyll <i>a/c</i>-binding Protein (FCP) of the haptophyte microalgae <i>Tisochrysis lutea</i> were performed by similarity analysis. The FCP family contains 52 <i>lhc</i> genes in <i>T. lutea</i>. FCP pigment binding site candidates were characterized on Lhcf protein monomers of <i>T. lutea</i>, which possesses at least nine chlorophylls and five fucoxanthin molecules, on average, per monomer. The expression of <i>T. lutea lhc</i> 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 <i>lhc</i> genes with nitrogen depletion. We observed that <i>T. lutea lhcx2</i> was only expressed at night, suggesting that its role is to protect \cells from return of light after prolonged darkness exposure.