Evidence for a common origin of chloroplasts with light-harvesting complexes of different pigmentation

THE red algae (Rhodophyta), which like cyanobacteria have only chlorophyll a and use phycobilisomes for light-harvesting 1,2 , are often considered to have originated independently of other photosynthetic eukaryotes, namely the chlorophyll a/b -containing Chlorophyta and the chlorophyll a/c -containing Chromophyta 3 . Here we report that the red alga Porphyridium cruentum has a chlorophyll a -containing antenna complex functionally associated with photosystem I, and that polypeptides of this antenna complex are immunologically related to those of higher-plant chlorophyll a/b complexes and to those of chromophyte fucoxanthin–chlorophyll a/c antenna complexes. This establishes a clear link between organisms containing phycobilisomes and those containing chlorophyll-based light-harvesting complexes and shows that these antennae can coexist in the same organism. Furthermore, it suggests that the light-harvesting proteins of all photosynthetic eukaryotes had a common origin and supports the idea that chloroplasts had a common ancestor 4–6 .