Abstract
Haptophyte algae acquired their plastid through the secondary endosymbiosis. Therefore they have many distinct characteristics compared to well-studied primary symbiotic algae and plants. We previously reported that the Haptophyte alga Emiliania huxleyi actively produces C4 compound via anaplerotic β-carboxylation reaction during photosynthesis. We also isolated a cDNA encoding pyruvate carboxylase (EhPYC) which is known as major β-carboxylation enzyme of non-photosynthetic organisms. In the present study, we confirmed the expression of EhPYC at protein level by western blot analysis. The recombinant EhPYC produced in a bacterium exhibits activity of PYC. The deduced EhPYC is predicted to have a bipartite plastid targeting signal that functions to deliver proteins into the four-membrane plastid of Haptophyte algae. Results of immunofluorescence labeling also supported the plastid localization of EhPYC. Genomes of green algae, diatoms, and brown alga possess homologs of PYC genes, but not in any species of cyanobacteria and higher plants. The wide distribution of PYC genes among eukaryotic algae suggests that PYC play crucial roles in the algal primary carbon metabolism.
