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Exclusive conservation of mitochondrial group II intron nad4i548 among liverworts and its use for phylogenetic studies in this ancient plant clade
Author(s) -
Volkmar U.,
GrothMalonek M.,
Heinrichs J.,
Muhle H.,
Polsakiewicz M.,
Knoop V.
Publication year - 2012
Publication title -
plant biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.871
H-Index - 87
eISSN - 1438-8677
pISSN - 1435-8603
DOI - 10.1111/j.1438-8677.2011.00499.x
Subject(s) - biology , phylogenetic tree , phylogenetics , clade , group ii intron , intron , sister group , evolutionary biology , mitochondrial dna , plant evolution , lineage (genetic) , genetics , gene , genome , rna , rna splicing
Liverworts occupy a pivotal position in land plant (embryophyte) phylogeny as the presumed earliest‐branching major clade, sister to all other land plants, including the mosses, hornworts, lycophytes, monilophytes and seed plants. Molecular support for this earliest dichotomy in land plant phylogeny comes from strikingly different occurrences of introns in mitochondrial genes distinguishing liverworts from all other embryophytes. Exceptionally, however, the nad 5 gene – the mitochondrial locus hitherto used most widely to elucidate early land plant phylogeny – carries a group I type intron that is shared between liverworts and mosses. We here explored whether a group II intron, the other major type of organellar intron, would similarly be conserved in position across the entire diversity of extant liverworts and could be of use for phylogenetic analyses in this supposedly most ancient embryophyte clade. To this end, we investigated the nad 4 gene as a candidate locus possibly featuring different introns in liverworts as opposed to the non‐liverwort embryophyte (NLE) lineage. We indeed found group II intron nad4i548 universally conserved in a wide phylogenetic sampling of 55 liverwort taxa, confirming clade specificity and surprising evolutionary stability of plant mitochondrial introns. As expected, intron nad4i548g2 carries phylogenetic information in its variable sequences, which confirms and extends previous cladistic insights on liverwort evolution. We integrate the new nad 4 data with those of the previously established mitochondrial nad 5 and the chloroplast rbc L and rps 4 genes and present a phylogeny based on the fused datasets. Notably, the phylogenetic analyses suggest a reconsideration of previous phylogenetic and taxonomic assignments for the genera Calycularia and Mylia and resolve a sister group relationship of Ptilidiales and Porellales.