Plastid RNA editing reduction accompanied with genetic variations in , a genus with diverse lifestyle modes.

Recent sequencing efforts have broadly uncovered the evolutionary trajectory of plastid genomes (plastomes) of flowering plants in diverse habitats, yet our knowledge of the evolution of plastid posttranscriptional modifications is limited. In this study, we generated 11 complete plastomes and performed ultra-deep transcriptome sequencing to investigate the co-evolution of plastid RNA editing and genetic variation in , a genus with diverse trophic lifestyles. Genome size and gene content is reduced in terrestrial and green mycoheterotrophic orchids relative to their epiphytic relatives. This could be partly due to extensive losses and pseudogenization of genes for the plastid NADH dehydrogenase-like complex, but independent pseudogenization of genes has also occurred in the epiphyte , which was reported to use strong crassulacean acid metabolism photosynthesis. RNA editing sites are abundant but variable in number among plastomes. The nearly twofold variation in editing abundance is mainly due to extensive reduction of ancestral editing sites in transcripts of terrestrial, mycoheterotrophic, and plastomes. The co-occurrence of editing reduction and pseudogenization in genes suggests functional constraints on editing machinery may be relaxed, leading to nonrandom loss of ancestral edited sites via reduced editing efficiency. This study represents the first systematic examination of RNA editing evolution linked to plastid genome variation in a single genus. We also propose an explanation for how genomic and posttranscriptional variations might be affected by lifestyle-associated ecological adaptation strategies in .