Figure 1. Phylogenetic analysis of the Tic22 gene family in plants and cyanobacteria.

Homologous sequences identified in whole genome sequence datasets from plants and cyanobacteria were analysed using the program MrBayes. The analysis showed a strong support for an origin of Tic22 in cyanobacteria, and revealed that all investigated plant and algal species include at least one member of the gene family. A gene duplication occurred at least 416–449 million years ago (indicated by a star), and resulted in two paralogous gene copies that have been conserved in all investigated angiosperms. Branch lengths in the two clades formed by the gene duplication are very similar (mean branch length and the 95% Highest Posterior Density [HPD] credibility interval are shown for a selection of branches), which indicates that the evolutionary rates of the two paralogous copies have been similar over an extensive period of time. A partial gene duplication (indicated with a red dot) is inferred to have happened after the split between red algae and other archaeplastida. The partially-duplicated gene of unknown function has been conserved in all investigated land plant species, but has not been found in any algal species. All Arabidopsis sequences are shown in red text. Posterior probability values appear above the branches, and the expected number of changes per site along the branches is indicated by the scale bar.