Carbon concentrating mechanism

Guilan Yu

Diatoms operate a very effective photosynthesis. They contribute up to 20% to global carbon fixation [1]. This is surprising because RubisCO enzymes found in diatoms have a CO2 half-saturation constant far above the average CO2 concentration in sea water [2,3]. This leads to the assumption that diatoms operate a carbon concentrating mechanism (CCM) [2,3]. Roberts et al. [4] have shown by 14C labeling that in the diatom Thalassiosira weissflogii the major initial carbon products are C3 and C4 compounds. Unfortunately, the mechanisms behind the carbon pathways in diatoms are still unclear.

Since the genome of the diatom Phaeodactylum tricornutum has been sequenced [5], genes encoding enzymes which are involved in both pathways could be detected [6]. Recent results suggest an active transport of inorganic carbon (Ci) from the cytoplasm into the chloroplast’s pyrenoid [7]. In this project, we are investigating the putative functions of selected carboxylases and decarboxylases (see figure below) to understand how they might contribute to photosynthesis in P. tricornutum.

Literature:

  1. Field et al. (1998) Science 281: 237–240.
  2. Badger et al. (1998) Can J Bot 76: 1052–1071.
  3. Riebesell et al. (1993) Nature 361: 249-251.
  4. Roberts et al. (2007) Plant Physiology 145: 230-235.
  5. Bowler et al. (2008): Nature 456: 239-244.
  6. Kroth et al. (2008) PLoS ONE 1: e1426.
  7. Hopkinson et al. (2011) PNAS 1018062108.
  8. Poulsen et al. (2005) FEBS Journal 272: 3413-3423.