MBE Advance Access originally published online on December 1, 2007
Molecular Biology and Evolution 2008 25(2):393-401; doi:10.1093/molbev/msm267
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Research Articles |
Functional Gene Losses Occur with Minimal Size Reduction in the Plastid Genome of the Parasitic Liverwort Aneura mirabilis
* Department of Ecology and Evolutionary Biology, University of Connecticut
Department of Biology, Penn State University
Genome Project Solutions, Hercules, California
Department of Energy Joint Genome Institute and University of California Lawrence Berkeley National Laboratory, Walnut Creek, California
|| Department of Biology, Utah State University
E-mail: norman.wickett{at}uconn.edu.
Accepted for publication November 20, 2007.
Aneura mirabilis is a parasitic liverwort that exploits an existing mycorrhizal association between a basidiomycete and a host tree. This unusual liverwort is the only known parasitic seedless land plant with a completely nonphotosynthetic life history. The complete plastid genome of A. mirabilis was sequenced to examine the effect of its nonphotosynthetic life history on plastid genome content. Using a partial genomic fosmid library approach, the genome was sequenced and shown to be 108,007 bp with a structure typical of green plant plastids. Comparisons were made with the plastid genome of Marchantia polymorpha, the only other liverwort plastid sequence available. All ndh genes are either absent or pseudogenes. Five of 15 psb genes are pseudogenes, as are 2 of 6 psa genes and 2 of 6 pet genes. Pseudogenes of cysA, cysT, ccsA, and ycf3 were also detected. The remaining complement of genes present in M. polymorpha is present in the plastid of A. mirabilis with intact open reading frames. All pseudogenes and gene losses co-occur with losses detected in the plastid of the parasitic angiosperm Epifagus virginiana, though the latter has functional gene losses not found in A. mirabilis. The plastid genome sequence of A. mirabilis represents only the second liverwort, and first mycoheterotroph, to have its plastid genome sequenced. We observed a pattern of genome evolution congruent with functional gene losses in parasitic angiosperms but suggest that its plastid genome represents a genome in the early stages of decay following the relaxation of selection pressures.
Key Words: Aneura mirabilis • Cryptothallus • parasitic plants • liverworts • bryophytes • chloroplast genome
Charles Delwiche, Associate Editor