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

Mikhail I Schelkunov,Maria D Logacheva,Maxim S Nuraliev

doi:10.7717/peerj.7500

Abstract

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 plastid genomes markedly differ from the plastid 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 other plants. The genome is highly reduced (18,622 base pairs vs. approximately 150 kbp in autotrophic plants) and possesses an extraordinarily high AT content, 86.8%, which is inferior only to AT contents of plastid genomes of Balanophora, a genus from the same family. 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 homologs from AT-rich plastid genomes of protists. Overall, the plastid genome of R. phalloides is one of the most unusual plastid genomes known.

Highlights

Though plants are generally considered photosynthetic organisms, there are several hundred plant species that have lost the ability to photosynthesize during the course of evolution (Westwood et al, 2010; Merckx et al, 2013)
The protein-coding gene content is quite typical for highly reduced plastid genomes of completely heterotrophic plants (Graham, Lam & Merckx, 2017; Wicke & Naumann, 2018)
Like several other highly reduced plastid genomes, it lacks rrn4.5 and rrn5— genes coding for two other RNAs of the ribosome—which poses the interesting puzzle of how the ribosome works without these genes in the plastid genome

Summary

Introduction

Though plants are generally considered photosynthetic organisms, there are several hundred plant species that have lost the ability to photosynthesize during the course of evolution (Westwood et al, 2010; Merckx et al, 2013). They feed either by parasitizing other plants or by obtaining nutrients from fungi. In addition to the completely heterotrophic plants, there are plants that combine the ability to photosynthesize with the heterotrophic lifestyle They are termed partial heterotrophs (or hemi-heterotrophs, or mixotrophs) in contrast to the former, which are termed complete heterotrophs (or holo-heterotrophs).

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