Regulation of Phaeodactylum plastid gene transcription

<p>Diatoms are a diverse group of photosynthetic unicellular algae with a plastid derived from red algae. As prolific primary producers in the ocean, diatoms fix as much carbon as all rainforests combined. The molecular mechanisms that contribute to the high photosynthetic productivity and ecological success of diatoms are however not yet fully understood. Using the model diatom <i>Phaeodactylum tricornutum</i>, here we show rhythmic transcript accumulation of plastid <i>psaA</i>, <i>psbA</i>, <i>petB</i>, and <i>atpB</i> genes as driven by a free running circadian clock. Treatment with the electron transport inhibitor 3-(3,4-dichlorophenyl)-1,1-dimethylurea overrides the circadian signal by markedly downregulating transcription of <i>psaA</i>, <i>petB</i>, and <i>atpB</i> genes but not the <i>psbA</i> gene. Changes in light quantity produce little change in plastid gene transcription while the effect of light quality seems modest with only the <i>psaA</i> gene responding in a pattern that is dependent on the redox state of the plastoquinone pool. </p>