Contrasting evolutionary histories of chloroplast 1 thioredoxins f and m

Fourteen thiorcdoxin sequences were used to construct a minimal phylogenctic tree by using parsimony. The bacterial thioredoxins clustered into three groups: one containing the photosynthctic purple bacteria. Escherichia and Corynebacterinm; a second containing the photosynthetic green bacterium, Chlorobium. and a third containing cyanobacteria. These groupings are similar to those generated from earlier 16s RNA analyses. Animal thioredoxins formed a fourth group. The two thioredoxins of chloroplasts ( f and m) showed contrasting phylogenetic patterns. As predicted from prior studies, spinach chloroplast thiorcdoxin m grouped with its counterparts from cyanobacteria and eukaryotic algae, but. unexpectedly, thioredoxin f grouped with the animal thioredoxins. The results indicate that, during evolution, thioredoxin m of contemporary photosynthctic eukaryotic cells was derived from a prokaryotic symbiont, whereas thioredoxin f descended from an ancestral eukaryote common to plants and animals. The findings illustrate the potential of thioredoxin as a phylogenetic marker and suggest a relationship between the animal and f-type thioredoxins.