Molecular evolution of plastid genomes in parasitic flowering plants

Wicke S, Naumann J

Zusammenfassung

Heterotrophic carbon acquisition is the most unusual lifestyle in plants, whereby the heterotrophs obtain water, nutrients, and macromolecules from either another plant or a fungus. Besides numerous morphological changes that accompany the transition to a fully heterotrophic lifestyle in plants, the so-called parasitic reduction syndrome manifests at the molecular level, especially in theplastidgenome. Here, we provide an overview of the sizes, architectures, and coding capacity of plastid genomes in heterotrophicland plants, with a major focus on flowering plants. Our compilation of plastomes of over 75 taxa covering 15 lineages of haustorial parasites and mycoheterotrophs reveals novel insights into the order of housekeeping gene losses, where apparently several plastid tRNA gene deletions precede the loss of ribosomal subunits. A comparison of the three major conceptual models of plastome degradation en route to heterotrophy in plants shows that plastid evolutionary trajectories are essentially convergent across lineages—independent of the feeding type. However, several questions regarding the series and timing of functional and physical gene losses remain unclear, in part because functional data are widely lacking. Nevertheless, the currently available evolutionary models of reductive plastome evolution provide excellent starting points for leaving the paths of descriptive science towards hypothesis-driven research.