Genomics and chloroplast evolution: what did cyanobacteria do for plants?

The complete genome sequences of cyanobacteria and of the higher plant Arabidopsis thaliana leave no doubt that the plant chloroplast originated, through endosymbiosis, from a cyanobacterium. But the genomic legacy of cyanobacterial ancestry extends far beyond the chloroplast itself, and persists in organisms that have lost chloroplasts completely.