Fundamental aspects of carbon fixation

Diatoms are responsible for about one quarter of global C sequestration, yet there are still many unanswered questions about how these organisms concentrate carbon around RuBisCO and prevent losses to photorespiration.  Coupled with careful control over CO2 availability, we’ve used transcript analysis and proteomics to elucidate the underlying mechanisms that contribute to diatoms’ important role in global biogeochemistry.  Our data reveal that diatoms respond to low CO2 by up-regulating PEPC transcripts and proteins (the first step of the C4 pathway, in which bicarbonate is fixed onto a 3-carbon organic acid to make a 4 carbon acid) but neither archetypical decarboxylation pathways are responsible for "C4" assisted photosynthesis in diatoms.  We are currently probing candidate proteins that may be responsible for completing this C4 cycle.