Fig. 6.

Schematic representation of two alternative scenarios for the origin of the nuclear-encoded plastid-targeted rpl20 gene in Passiflora. (A) Duplication of nuclear-encoded mitochondrial rpl20 followed by gain of a plastid-targeted TP by the duplicated copy, followed by the loss of rpl20 from the plastome. (B) Transfer of plastid rpl20 to nucleus that includes acquisition of a TP and an intron. A possible scenario for intron gain could be intron transfer from nuclear-encoded mitochondrial rpl20 due to sequence homology with nuclear-transferred rpl20, which is shown with dotted lines. Gain of a TP by nuclear-transferred plastid rpl20 facilitates plastid localization of its product. Gray and white boxes represent exons for the nuclear and plastid genes, respectively. Black lines between the exons represent introns. Dotted lines with arrowheads indicate proteins that are targeted either to mitochondria or plastids. Major evolutionary events are shown in thick black arrows and descriptions are provided. The figure is not drawn to scale. Abbreviations, Nu, nucleus; Mt, mitochondrion; Pt, Plastid.