Systematics Section / ASPT
Duff, R. Joel , Moore, Francisco .
The maintenance and evolution of RNA editing and its effects on phylogeny reconstruction in hornworts.
Phylogenetic analyses of hornworts utilizing a number of chloroplast and mitochondrial protein coding genes have resulted in a well resolved phylogeny in which Leiosporoceros is resolved as a sister taxa to the hornworts. Subsequent examinations of edited sites in rbcL (chloroplast) and nad5 (mitochondrion) revealed highly divergent rates of editing among hornwort lineages. In particular, Leiosporoceros lacks edited sites in rbcL transcripts and exhibits far fewer sites in partial nad5 sequences. Analyses following the removal of edited sites from rbcL and nad5 data sets still resolve the same hornwort relationships except that Leiosporoceros is nested among the hornworts rather than sister to them. Given the apparent effects of edited sites on the resolution of Leiosporoceros it is crucial to know if the present reduced level of editing in Leiosporoceros is an ancestral or derived feature. If Leiosporoceros represents the ancestral editing condition then all edited sites among hornworts represent derived characters and Leiosporoceros will resolve as sister to the hornwort clade. But if Leiosporoceros is a derived taxon with its high editing subsequently lost this would imply strong selection driving these sites toward reversal to their ancestral state. In effect the Leiosporoceros transcript should resemble the ancestral hornwort condition at the edited positions. Since the edited sites provide a large number of the phylogenetic informative data, phylogenetic analyses including these data would likely not resolve the correct hornwort topology. Therefore, resolution of Leiosporoceros is affected by the direction of evolution of the edited sites and hence further resolution of hornwort phylogeny will require the use of sequences that are not affected by RNA editing (rDNA and introns). Only when the position of Leiosporoceros can be definitively identified, will we be able to determine if the low editing rate is ancestral or derived in this genus and hornworts in general.
1 - University of Akron, Biology Department, Akron, Ohio, 443225-3908, USA
Land Plant Evolution.
Presentation Type: Paper
Location: Cottonwood B (Snowbird Center)
Date: Wednesday, August 4th, 2004
Time: 3:45 PM