Phylotranscriptomic analysis of the origin and early diversification of land plantsNorman J. Wickett, Siavash Mirarab, Nam Nguyen et al.|Proceedings of the National Academy of Sciences|2014 Reconstructing the origin and evolution of land plants and their algal relatives is a fundamental problem in plant phylogenetics, and is essential for understanding how critical adaptations arose, including the embryo, vascular tissue, seeds, and flowers. Despite advances in molecular systematics, some hypotheses of relationships remain weakly resolved. Inferring deep phylogenies with bouts of rapid diversification can be problematic; however, genome-scale data should significantly increase the number of informative characters for analyses. Recent phylogenomic reconstructions focused on the major divergences of plants have resulted in promising but inconsistent results. One limitation is sparse taxon sampling, likely resulting from the difficulty and cost of data generation. To address this limitation, transcriptome data for 92 streptophyte taxa were generated and analyzed along with 11 published plant genome sequences. Phylogenetic reconstructions were conducted using up to 852 nuclear genes and 1,701,170 aligned sites. Sixty-nine analyses were performed to test the robustness of phylogenetic inferences to permutations of the data matrix or to phylogenetic method, including supermatrix, supertree, and coalescent-based approaches, maximum-likelihood and Bayesian methods, partitioned and unpartitioned analyses, and amino acid versus DNA alignments. Among other results, we find robust support for a sister-group relationship between land plants and one group of streptophyte green algae, the Zygnematophyceae. Strong and robust support for a clade comprising liverworts and mosses is inconsistent with a widely accepted view of early land plant evolution, and suggests that phylogenetic hypotheses used to understand the evolution of fundamental plant traits should be reevaluated.
A record-setting mitogenome in the holoparasitic plant Balanophora yakushimensis accompanied by exceptional loss of organellar DNA repair and recombination genesBACKGROUND: Despite only limited sampling, the holoparasitic plant family Balanophoraceae harbors extreme mito-genome diversity and also has exceptionally divergent plastomes. We therefore sequenced the mitochondrial, plastid, and nuclear genomes of Balanophora yakushimensis and its transcriptome. RESULTS: At 1.1 Mb, the B. yakushimensis mitogenome is one of the largest known mitogenomes. Driving this expansion and generating the most repeat-rich mitogenome in land plants are many large (up to 200 kb) duplications and a massive proliferation of short, AT-rich repeated sequences. The repeat proliferation, in conjunction with a highly elevated and unusually AT-biased mutation rate, has produced what is by far the most AT-rich land-plant mito-genome. These invasive repeats also created giant introns, unprecedented in size for organelles, and greatly expanded all rDNA exons. We discovered a record-low, for all genomes, transition/transversion ratio (0.12) in B. yakushimensis mtDNA and documented a 26-fold range in this ratio across angiosperm mitogenomes. The B. yakushimensis nuclear genome has lost exceptionally many genes that function in organellar DNA recombination, repair, and replication (RRR). We discuss ways in which these losses-and other genetic alterations as well as non-genetic ones-may or may not be related to the unusual features of both its mitochondrial and plastid genomes. CONCLUSIONS: The mitogenome of B. yakushimensis possesses many exceptional, indeed record-setting properties. The unprecedented loss of nuclear genes for organellar DNA RRR may explain some of these unusual features. These findings expand the boundaries of mitogenome deviancy and raise outstanding questions about the forces driving such extravagantly diversifying evolution.