Variation in frequency of plastid RNA editing within Adiantum implies rapid evolution in fern plastomes

Premise Recent studies of plant RNA editing have demonstrated that the number of editing sites can vary widely among large taxonomic groups (orders, families). Yet, very little is known about intrageneric variation in frequency of plant RNA editing, and no study has been conducted in ferns. Methods We determined plastid RNA-editing counts for two species of Adiantum (Pteridaceae), A. shastense and A. aleuticum, by implementing a pipeline that integrated read-mapping and SNP-calling software to identify RNA-editing sites. We then compared the edits found in A. aleuticum and A. shastense with previously published edits from A. capillus-veneris by generating alignments for each plastid gene. Results We found direct evidence for 505 plastid RNA-editing sites in A. aleuticum and 509 in A. shastense, compared with 350 sites in A. capillus-veneris. We observed striking variation in the number and location of the RNA-editing sites among the three species, with reverse (U-to-C) editing sites showing a higher degree of conservation than forward (C-to-U) sites. Additionally, sites involving start and stop codons were highly conserved. Conclusions Variation in the frequency of RNA editing within Adiantum implies that RNA-editing sites can be rapidly gained or lost throughout evolution. However, varying degrees of conservation between both C-to-U and U-to-C sites and sites in start or stop codons, versus other codons, hints at the likely independent origin of both types of edits and a potential selective advantage conferred by RNA editing.

Automated summary

Recent studies of plant RNA editing have shown significant variation in editing sites among different taxonomic groups, with ferns remaining largely unexplored. By analyzing the RNA editing in two Adiantum species and comparing them with a previously studied species, it was found that there is variation in both the number and location of editing sites among the species, with U-to-C editing sites showing higher conservation than C-to-U sites, especially those affecting start and stop codons. This suggests that RNA editing can evolve rapidly within Adiantum species, with certain types of edits potentially conferring selective advantages.