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AbstractSuperbubbles are acyclic induced subgraphs of a digraph with single entrance and exit that naturally arise in the context of genome assembly and the analysis of genome alignments in computational biology. These structures can be computed in linear time and are confined to non-symmetric digraphs. We demonstrate empirically that graph parameters derived from superbubbles provide a convenient means of distinguishing different classes of real-world graphical models, while being largely unrelated to simple, commonly used parameters.

[BACKGROUND]: Lacerta viridis and Lacerta bilineata are sister species of European green lizards (eastern and western clades, respectively) that, until recently, were grouped together as the L. viridis complex. Genetic incompatibilities were observed between lacertid populations through crossing experiments, which led to the delineation of two separate species within the L. viridis complex. The population history of these sister species and processes driving divergence are unknown. We constructed the first high-quality de novo genome assemblies for both L. viridis and L. bilineata through Illumina and PacBio sequencing, with annotation support provided from transcriptome sequencing of several tissues. To estimate gene flow between the two species and identify factors involved in reproductive isolation, we studied their evolutionary history, identified genomic rearrangements, detected signatures of selection on non-coding RNA, and on protein-coding genes. [FINDINGS]: Here we show that gene flow was primarily unidirectional from L. bilineata to L. viridis after their split at least 1.15 million years ago. We detected positive selection of the non-coding repertoire; mutations in transcription factors; accumulation of divergence through inversions; selection on genes involved in neural development, reproduction, and behavior, as well as in ultraviolet-response, possibly driven by sexual selection, whose contribution to reproductive isolation between these lacertid species needs to be further evaluated. [CONCLUSION]: The combination of short and long sequence reads resulted in one of the most complete lizard genome assemblies. The characterization of a diverse array of genomic features provided valuable insights into the demographic history of divergence among European green lizards, as well as key species differences, some of which are candidates that could have played a role in speciation. In addition, our study generated valuable genomic resources that can be used to address conservation-related issues in lacertids. ; Thank the DFG for funding under the project SFB 1052 "Obesity Mechanisms" (project number: 209933828). P.F.S, K.N and M.B.W.C thank the DFG for funding under the grant SPP 1738 (project numbers: STA 850/19-1 and STA 920/6-1). K.N. and R.F. thank the Volkswagen Foundation for funding within the frame work "Support for Europe." R.F. was financed by FCT (grant SFRH/BPD/89313/2012) and is currently funded by the European Union's Horizon 2020 Research and Innovation Programme, under the Marie Sklodowska-Curie grant agreement 706376. KL is supported by an Independent Research fellowship from the Natural Environmental Research Council (NERC) UK (NE/L011522/1).

Thlaspi arvense (field pennycress) is being domesticated as a winter annual oilseed crop capable of improving ecosystems and intensifying agricultural productivity without increasing land use. It is a selfing diploid with a short life cycle and is amenable to genetic manipulations, making it an accessible field-based model species for genetics and epigenetics. The availability of a high-quality reference genome is vital for understanding pennycress physiology and for clarifying its evolutionary history within the Brassicaceae. Here, we present a chromosome-level genome assembly of var. MN106-Ref with improved gene annotation and use it to investigate gene structure differences between two accessions (MN108 and Spring32-10) that are highly amenable to genetic transformation. We describe non-coding RNAs, pseudogenes and transposable elements, and highlight tissue-specific expression and methylation patterns. Resequencing of forty wild accessions provided insights into genome-wide genetic variation, and QTL regions were identified for a seedling colour phenotype. Altogether, these data will serve as a tool for pennycress improvement in general and for translational research across the Brassicaceae. ; This material is based upon work that is supported by the Minnesota Department of Agriculture (J.A., K.F., R.C.) and by the National Institute of Food and Agriculture, U.S. Department of Agriculture, under award numbers 2018-67009-27374 (J.A., R.C., K.F.), and 2019-67009-29004 (M.D.M, J.S.) and the Agriculture and Food Research Initiative Competitive Grant No. 2019-69012-29851 (M.D.M, R.C., J.S.). This research was supported by the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research, Genomics Science Program grant no. DE-SC0021286 (M.D.M, R.C.). This work was further funded by the Austrian Academy of Sciences (C.B., I.R.A., K.J., D.R.C.); the Max Planck Society (D.W., A.C.G., P.C.B., C.L.); the European Union's Horizon 2020 research and innovation programme by the European ...