Many Parallel Losses of infA from Chloroplast DNA during Angiosperm Evolution with Multiple Independent Transfers to the Nucleus

We used DNA sequencing and gel blot surveys to assess the integrity of the chloroplast gene infA, which codes for translation initiation factor 1, in >300 diverse angiosperms. Whereas most angiosperms appear to contain an intact chloroplast infA gene, the gene has repeatedly become defunct in approximately 24 separate lineages of angiosperms, including almost all rosid species. In four species in which chloroplast infA is defunct, transferred and expressed copies of the gene were found in the nucleus, complete with putative chloroplast transit peptide sequences. The transit peptide sequences of the nuclear infA genes from soybean and Arabidopsis were shown to be functional by their ability to target green fluorescent protein to chloroplasts in vivo. Phylogenetic analysis of infA sequences and assessment of transit peptide homology indicate that the four nuclear infA genes are probably derived from four independent gene transfers from chloroplast to nuclear DNA during angiosperm evolution. Considering this and the many separate losses of infA from chloroplast DNA, the gene has probably been transferred many more times, making infA by far the most mobile chloroplast gene known in plants.