Abstract
Many diatoms possess inorganic carbon concentrating mechanism (CCM), which might be co-operate with C4 mechanism. It is previously shown that carbonic anhydrase1 (PtCA1) might play a crucial role in CCM and these systems are regulated by CO2 concentration in the medium in P. tricornutum.
To determine the function of PtCA1, wild-type cells were transformed with vector containing ptca1-egfp fusion driven with a constitutive promoter fcpA (Pt2fcpApCA1GFPb). PtCA1 is known to be sorted to plastid as assembled particles on the surface of girdle lamella by the function of bipartite N-terminal presequence, which comprises of putative ER signal followed by a transit peptide-like domain. In wild-type cells, PtCA1 was repressed in 5% CO2, whereas PtCA1-GFP fusion in Pt2fcpApCA1GFPb was constitutively expressed in 5% CO2. Although Pt2fcpApCA1GFPb grew normally in 5% CO2 and air, the photosynthetic rate of Pt2fcpApCA1GFPb was remarkably suppressed when high CO2-grown cells were transferred to air.
