Abstract
Diatoms are one of the major photoautotrophic organisms in the hydrosphere. Similarly to other microscopic algae, many diatoms have been reported to possess inorganic carbon concentrating mechanism, which confers cells to operate high-affinity photosynthesis for dissolved inorganic carbon. In the marine diatom Phaeodactylum tricornutum, it was reported that intracellular carbonic anhydrase (CA) was essential to operate the high-affinity photosynthesis. To date a low-CO2-inducible β-type CA (ptca1) was isolated and shown to be localized at the chloroplast. Recently, we identified the new β-CA gene (ptca2) which was found to be highly homologous to ptca1. Quantitative analysis of mRNA accumulation of ptca2 exhibited a significant level of accumulation even under 5% CO2 and the accumulation level increased 3.5-fold upon acclimation to low CO2. This induction level was less significant as compared to that of ptca1. The promoter regions of two genes which are required for CO2 responsibility of expression were further investigated.
