The trade‐off between the light‐harvesting and photoprotective functions of fucoxanthin‐chlorophyll proteins dominates light acclimation in <i>Emiliania huxleyi</i> (clone <scp>CCMP</scp> 1516)

<jats:title>Summary</jats:title><jats:p> <jats:list list-type="bullet"> <jats:list-item><jats:p>Mechanistic understanding of the costs and benefits of photoacclimation requires knowledge of how photophysiology is affected by changes in the molecular structure of the chloroplast.</jats:p></jats:list-item> <jats:list-item><jats:p>We tested the hypothesis that changes in the light dependencies of photosynthesis, nonphotochemical quenching and <jats:styled-content style="fixed-case">PSII</jats:styled-content> photoinactivation arises from changes in the abundances of chloroplast proteins in <jats:italic>Emiliania huxleyi</jats:italic> strain <jats:styled-content style="fixed-case">CCMP</jats:styled-content> 1516 grown at 30 (Low Light; <jats:styled-content style="fixed-case">LL</jats:styled-content>) and 1000 (High Light; <jats:styled-content style="fixed-case">HL</jats:styled-content>) μmol photons m<jats:sup>−2</jats:sup> s<jats:sup>−1</jats:sup> photon flux densities.</jats:p></jats:list-item> <jats:list-item><jats:p>Carbon‐specific light‐saturated gross photosynthesis rates were not significantly different between cells acclimated to <jats:styled-content style="fixed-case">LL</jats:styled-content> and <jats:styled-content style="fixed-case">HL</jats:styled-content>. Acclimation to <jats:styled-content style="fixed-case">LL</jats:styled-content> benefited cells by increasing biomass‐specific light absorption and gross photosynthesis rates under low light, whereas acclimation to <jats:styled-content style="fixed-case">HL</jats:styled-content> benefited cells by reducing the rate of photoinactivation of <jats:styled-content style="fixed-case">PSII</jats:styled-content> under high light. Differences in the relative abundances of proteins assigned to light‐harvesting (Lhcf), photoprotection (<jats:styled-content style="fixed-case">LI</jats:styled-content>818‐like), and the photosystem <jats:styled-content style="fixed-case">II</jats:styled-content> (<jats:styled-content style="fixed-case">PSII</jats:styled-content>) core complex accompanied differences in photophysiology: specifically, Lhcf:<jats:styled-content style="fixed-case">PSII</jats:styled-content> was greater under <jats:styled-content style="fixed-case">LL</jats:styled-content>, whereas <jats:styled-content style="fixed-case">LI</jats:styled-content>818:<jats:styled-content style="fixed-case">PSII</jats:styled-content> was greater in <jats:styled-content style="fixed-case">HL</jats:styled-content>.</jats:p></jats:list-item> <jats:list-item><jats:p>Thus, photoacclimation in <jats:italic>E. huxleyi</jats:italic> involved a trade‐off amongst the characteristics of light absorption and photoprotection, which could be attributed to changes in the abundance and composition of proteins in the light‐harvesting antenna of <jats:styled-content style="fixed-case">PSII</jats:styled-content>.</jats:p></jats:list-item> </jats:list> </jats:p>