Abstract
BackgroundThe moss Physcomitrella patens (Hedw.) Bruch & Schimp. is an important experimental model system for evolutionary-developmental studies. In order to shed light on the evolutionary history of Physcomitrella and related species within the Funariaceae, we analyzed the natural genetic diversity of the Physcomitrium-Physcomitrella species complex.ResultsMolecular analysis of the nuclear single copy gene BRK1 reveals that three Physcomitrium species feature larger genome sizes than Physcomitrella patens and encode two expressed BRK1 homeologs (polyploidization-derived paralogs), indicating that they may be allopolyploid hybrids. Phylogenetic analyses of BRK1 as well as microsatellite simple sequence repeat (SSR) data confirm a polyphyletic origin for three Physcomitrella lineages. Differences in the conservation of mitochondrial editing sites further support hybridization and cryptic speciation within the Physcomitrium-Physcomitrella species complex.ConclusionsWe propose a revised classification of the previously described four subspecies of Physcomitrella patens into three distinct species, namely Physcomitrella patens, Physcomitrella readeri and Physcomitrella magdalenae. We argue that secondary reduction of sporophyte complexity in these species is due to the establishment of an ecological niche, namely spores resting in mud and possible spore dispersal by migratory birds. Besides the Physcomitrium-Physcomitrella species complex, the Funariaceae are host to their type species, Funaria hygrometrica, featuring a sporophyte morphology which is more complex. Their considerable developmental variation among closely related lineages and remarkable trait evolution render the Funariaceae an interesting group for evolutionary and genetic research.
Highlights
The moss Physcomitrella patens (Hedw.) Bruch & Schimp. is an important experimental model system for evolutionary-developmental studies
In order to test the polyphyletic origin of the genus Physcomitrella and to analyze whether monophyletic groups corresponding to species can be resolved within Physcomitrella, we performed phylogenetic analyses of a nuclear single copy gene (BRK1) [13] and microsatellite simple sequence repeat (SSR) data amplified from numerous accessions covering all four Physcomitrella subspecies and further Funariaceae
Most differences between the homeologs occurred in the single intron, while in the case of P. collenchymatum and P. eurystomum polymorphisms occurred in the exons (Additional file 3: Figure S1, Table 3)
Summary
The moss Physcomitrella patens (Hedw.) Bruch & Schimp. is an important experimental model system for evolutionary-developmental studies. We examine patterns of divergence among relatives of the moss Physcomitrella patens (Hedw.) Bruch & Schimp., the first bryophyte with completely sequenced and well-annotated nuclear, variable but overlapping phenotypic characteristics, a revised classification of the genus Physcomitrella was subsequently proposed by Tan [5], which described Physcomitrella as one single polymorphic species with four subspecies, namely P. patens ssp. The majority of bryologists accept three separate species, namely Physcomitrella patens, P. readeri and P. magdalenae De Sloover. P. patens has a wide distribution in the Northern Hemisphere, P. readeri is found in California (North America), Australia and Japan [8], while P. magdalenae has been reported from Rwanda, Africa [9,10]. Recent data suggest that the Physcomitrella phenotype arose three times within the Physcomitrium-Physcomitrella species complex, based on phylogenetic analyses of nuclear, chloroplast, and mitochondrial DNA sequence data [11,12]. In order to test the polyphyletic origin of the genus Physcomitrella and to analyze whether monophyletic groups corresponding to species can be resolved within Physcomitrella, we performed phylogenetic analyses of a nuclear single copy gene (BRK1) [13] and microsatellite simple sequence repeat (SSR) data amplified from numerous accessions covering all four Physcomitrella subspecies and further Funariaceae
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