Rhopalocnemis phalloides has one of the most reduced and mutated plastid genomes known

Although most plant species are photosynthetic, several hundred species have lost the ability to photosynthesize and instead obtain nutrients via various types of heterotrophic feeding. Their genomes, especially plastid genomes, markedly differ from the genomes of photosynthetic plants. In this work, we describe the sequenced plastid genome of the heterotrophic plant Rhopalocnemis phalloides, which belongs to the family Balanophoraceae and feeds by parasitizing on other plants. The genome is highly reduced (18 622 base pairs versus approximately 150 kilobase pairs in autotrophic plants) and possesses an outstanding AT content, 86.8%, the highest of all sequenced plant plastid genomes. The gene content of this genome is quite typical of heterotrophic plants, with all of the genes related to photosynthesis having been lost. The remaining genes are notably distorted by a high mutation rate and the aforementioned AT content. The high AT content has led to sequence convergence between some of the remaining genes and their homologues from AT-rich plastid genomes of protists. Overall, the plastid genome of R. phalloides is one of the most unusual plastid genomes known.