A proposed model for the gene transfer and activation of rice rpl6. The numbers in the figure correspond to those of the subtitles in the Discussion. The mitochondrial rpl6-derived coding region is colored with orange. The coding regions of nucleus-encoded rpl6 copies with mitochondrial targeting ability are colored with red. The 3'-part of the intron is indicated by a thick black line. Other elements are indicated as in Figure 1. The predicted evolutionary timing of each event is indicated on the right.