Phototropins maintain robust circadian oscillation of <scp>PSII</scp> operating efficiency under blue light

<jats:title>Summary</jats:title><jats:p>The circadian system allows plants to coordinate metabolic and physiological functions with predictable environmental variables such as dusk and dawn. This endogenous oscillator is comprised of biochemical and transcriptional rhythms that are synchronized with a plant's surroundings via environmental signals, including light and temperature. We have used chlorophyll fluorescence techniques to describe circadian rhythms of <jats:styled-content style="fixed-case">PSII</jats:styled-content> operating efficiency (<jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/tpj12947-math-0002.png" xlink:title="urn:x-wiley:09607412:media:tpj12947:tpj12947-math-0002" />) in the chloroplasts of <jats:italic>Arabidopsis thaliana</jats:italic>. These <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/tpj12947-math-0003.png" xlink:title="urn:x-wiley:09607412:media:tpj12947:tpj12947-math-0003" /> oscillations appear to be influenced by transcriptional feedback loops previously described in the nucleus, and are induced by rhythmic changes in photochemical quenching over circadian time. Our work reveals that a family of blue photoreceptors, phototropins, maintain robust rhythms of <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/tpj12947-math-0004.png" xlink:title="urn:x-wiley:09607412:media:tpj12947:tpj12947-math-0004" /> under constant blue light. As phototropins do not influence circadian gene expression in the nucleus our imaging methodology highlights differences between the modulation of circadian outputs in distinct subcellular compartments.</jats:p>