title: Rapid evolution of RNA editing sites in a small non-essential plastid gene.
abstract: Chloroplast RNA editing proceeds by C-to-U transitions at highly specific sites. Here, we provide a phylogenetic analysis of RNA editing in a small plastid gene, petL, encoding subunit VI of the cytochrome b6f complex. Analyzing representatives from most major groups of seed plants, we find an unexpectedly high frequency and dynamics of RNA editing. High-frequency editing has previously been observed in plastid ndh genes, which are remarkable in that their mutational inactivation does not produce an obvious mutant phenotype. In order to test the idea that reduced functional constraints allow for more flexible evolution of RNA editing sites, we have created petL knockout plants by tobacco chloroplast transformation. We find that, in the higher plant tobacco, targeted inactivation of petL does not impair plant growth under a variety of conditions markedly contrasting the important role of petL in photosynthesis in the green alga Chlamydomonas reinhardtii. Together with a low number of editing sites in plastid genes that are essential to gene expression and photosynthetic activity, these data suggest that RNA editing sites may evolve more readily in those genes whose transitory loss of function can be tolerated. Accumulated evidence for this 'relative neutrality hypothesis for the evolution of plastid editing sites' is discussed.
authors.affiliation: Westfälische Wilhelms-Universität Münster, Institut für Biochemie und Biotechnologie der Pflanzen, Hindenburgplatz 55, D-48143 Münster, Germany.
authors.forename: Andreas
authors.initials: A
authors.lastname: Fiebig
authors.forename: Sandra
authors.initials: S
authors.lastname: Stegemann
authors.forename: Ralph
authors.initials: R
authors.lastname: Bock
mesh_terms: D001483:Base Sequence; D045346:Cytochrome b6f Complex / Q000235:genetics; D019143:Evolution, Molecular; D017343:Genes, Plant; D008957:Models, Genetic; D008969:Molecular Sequence Data; D010802:Phylogeny; D017393:RNA Editing; D018747:RNA, Chloroplast / Q000145:classification / Q000235:genetics* / Q000378:metabolism; D012333:RNA, Messenger / Q000737:chemistry / Q000145:classification; D016415:Sequence Alignment; D014026:Nicotiana / Q000235:genetics
chemical_list: D018747:RNA, Chloroplast; D012333:RNA, Messenger; D045346:Cytochrome b6f Complex