Plastid Genomes of Parasitic Plants: A Trail of Reductions and Losses

Abstract

In contrast to plant mitochondrial genomes, which possess a high degree of plasticity, plastid genomes (plastomes) across photosynthetically active species are characterized by a remarkable conservation of structure, coding capacity, gene order, and intron content. Exceptions to the general pattern, however, are seen in parasitic species that have abandoned photosynthesis as the main energy source and live on other organisms, mainly other plants or algae. The relief from the selective pressure normally exerted by photosynthesis is reflected in a “plastomic striptease” that concerns the loss of coding sequences, introns, RNA-editing sites, and regulatory sequences from the plastid genome in higher plants and has, in extreme cases of nonphotosynthetic algal descendents, resulted in the loss of the entire organelle. This review attempts to give an overview over the trail of plastomic losses and reductions in parasitic species of the plant kingdom, with a main focus on higher plants.