Ins and outs of plastid genome evolution.

Recent findings have established cracks in the straight-laced image of the plastid genome as a molecule whose sole function is photosynthesis and whose gene content is highly conserved. Genes for numerous non-photosynthetic functions have been identified. Algal plastid genomes contain many genes with no homologs in angiosperms, and the recent transfer of genes from the plastid to the nuclear genome has been described. Wholesale abandonment of genes encoding photosynthetic and gene-expression functions has occurred in the plastid genomes of a non-green plant and alga. The origins of plastid DNA, its use in phylogenetic studies, and the origins of plastid introns are also reviewed.