Genomic and biochemical analysis of lipid biosynthesis in Cyanophora paradoxa: Limited role of chloroplast in fatty acid synthesis.

Archaeplastida, a group of photosynthetic organisms with primary plastids, consists of green algae (plus plants), red algae, and glaucophytes. In contrast to green and red algae, information on lipids and lipid biosynthesis still needs to be included in the glaucophytes. The chloroplast is the site of photosynthesis and fatty acid synthesis in all photosynthetic organisms known to date. However, the genomic data of the glaucophyte Cyanophora paradoxa suggested the lack of acetyl CoA carboxylase and most components of fatty acid synthase in the chloroplast. Instead, multifunctional fatty acid synthase and acetyl CoA carboxylase are likely to reside in the cytosol. To examine this hypothesis, we measured fatty acid synthesis in isolated chloroplasts and whole cells using stable isotope labeling. The chloroplasts had very low activity of fatty acid synthesis, if any. Most processes of fatty acid synthesis, including elongation and desaturation, must be performed within the cytosol, and the fatty acids imported into the chloroplasts are assembled into the chloroplast lipids by the enzymes common to other algae and plants. Cyanophora paradoxa is a rare organism in which fatty acid synthesis and photosynthesis are not tightly linked. This could question the common origin of these two biosynthetic processes in Archaeplastida.