GetOrganelle is a state-of-the-art toolkit to accurately assemble organelle genomes from whole genome sequencing data. It recruits organelle-associated reads using a modified “baiting and iterative mapping” approach, conducts de novo assembly, filters and disentangles the assembly graph, and produces all possible configurations of circular organelle genomes. For 50 published plant datasets, we are able to reassemble the circular plastomes from 47 datasets using GetOrganelle. GetOrganelle assemblies are more accurate than published and/or NOVOPlasty-reassembled plastomes as assessed by mapping. We also assemble complete mitochondrial genomes using GetOrganelle. GetOrganelle is freely released under a GPL-3 license (
 https://github.com/Kinggerm/GetOrganelle
 ).

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GetOrganelle: a fast and versatile toolkit for accurate de novo assembly of organelle genomes

Chloroplasts play a crucial role in sustaining life on earth. The availability of over 800 sequenced chloroplast genomes from a variety of land plants has enhanced our understanding of chloroplast biology, intracellular gene transfer, conservation, diversity, and the genetic basis by which chloroplast transgenes can be engineered to enhance plant agronomic traits or to produce high-value agricultural or biomedical products. In this review, we discuss the impact of chloroplast genome sequences on understanding the origins of economically important cultivated species and changes that have taken place during domestication. We also discuss the potential biotechnological applications of chloroplast genomes.

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Chloroplast genomes: diversity, evolution, and applications in genetic engineering

The chloroplast genome of Pelargonium e hortorum has beencompletely sequenced. It maps as a circular molecule of 217,942 bp, andis both the largest and most rearranged land plant chloroplast genome yetsequenced. It features two copies of a greatly expanded inverted repeat(IR) of 75,741 bp each, and consequently diminished single copy regionsof 59,710 bp and 6,750 bp. It also contains two different associations ofrepeated elements that contribute about 10 percent to the overall sizeand account for the majority of repeats found in the genome. Theyrepresent hotspots for rearrangements and gene duplications and include alarge number of pseudogenes. We propose simple models that account forthe major rearrangements with a minimum of eight IR boundary changes and12 inversions in addition to a several insertions of duplicated sequence.The major processes at work (duplication, IR expansion, and inversion)have disrupted at least one and possibly two or three transcriptionaloperons, and the genes involved in these disruptions form the core of thetwo major repeat associations. Despite the vast increase in size andcomplexity of the genome, the gene content is similar to that of otherangiosperms, with the exceptions of a large number of pseudogenes as partof the repeat associations, the recognition of two open reading frames(ORF56 and ORF42) more » in the trnA intron with similarities to previouslyidentified mitochondrial products (ACRS and pvs-trnA), the loss of accDand trnT-GGU, and in particular, the lack of a recognizably functionalrpoA. One or all of three similar open reading frames may possibly encodethe latter, however. « less

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The complete chloroplast genome sequence of Pelargonium xhortorum: Or ganization and evolution of the largest and most highlyrearranged chloroplast genome of land plants

Background: Chloroplast genes and genomes are the most important genomic data for plant phylogeny and DNA barcoding. Since the rapid development of high throughput sequencing technologies, it is cheap to get the low coverage data of whole genome, which is enough to assemble a complete chloroplast genome. To date, there are many assembly processes/pipelines described to assemble a complete chloroplast genome. In this study, we reported a simple and fast procedure to assemble a circular chloroplast genome using GetOrganelle pipeline. Findings: The GetOrganelle pipeline consists of four steps: 1) recruiting plastid-like reads; 2) de novo assembly using SPAdes; 3) filtering plastid-like contigs; and 4) visualizing and editing de novo assembly graph. Of them, the first three steps can be fulfilled automatically just using a combined command; and the fourth step is to visualize and evaluate the assemblies. Of 57 tested species with public datasets, we directly reassembled the circular chloroplast genome in 47 species. The eight non-circular species having break points, which may be caused by mononucleotide or dinonucleotide repeats, or small reads pool. In addition, we successfully assembled the circular chloroplast genome for the other 903 species of angiosperms using this pipeline, representing 41 families and 358 genera. Conclusion: The GetOrganelle pipeline is an effective way for land plants to assemble the circular chloroplast genome, without needs for reference-guided scaffolding, gap filling nor start-end point closing. This pipeline can be also applied to assemble mitochondrial genomes and nuclear Ribosomal DNAs using genome skimming data.

https://www.biorxiv.org/content/biorxiv/early/2018/03/09/256479.full.pdf

GetOrganelle: a simple and fast pipeline for de novo assembly of a complete circular chloroplast genome using genome skimming data

Quercus is considered as one of the most important genera in the Northern Hemisphere as its economic and ecological importance. Oaks are taxonomically perplexing due to interspecific shared morphological traits and intraspecific morphological variation, which mainly attributed to hybridization. Universal plastid markers could not provide sufficient variable sites to explore the phylogeny of this genus and chloroplast genome-scale data proved to be useful to resolve intractable phylogenetic relationships. In this study, four complete chloroplast genomes of Quercus species were sequenced and one published chloroplast genomes of Q. baronii was retrieved for comparative analyses. The sizes of these five chloroplast genomes ranged from 161,072 bp (Q. baronii) to 161,237 bp (Q. dolicholepis), which has been identified the gene organization, gene order and GC content are similar to other published Fagaceae species. We analyzed the nucleotide substitution, indels and repeats in chloroplast genomes. The detection of 19 relatively highly variable regions provides potential plastid markers for further taxonomic and phylogenetic study within Quercus. We future observed that 4 genes (ndhA, ndhK, petA and ycf1) were subjected to positive selection. Finally, the phylogenetic relationships of the published Quercus species inferred from chloroplast genomes obtained moderate-to-high supports, indicating that chloroplast genome data may be useful to resolve the relationships of this genus.

/pdf/comparative-analysis-of-the-complete-chloroplast-genomes-of-1zqel1vyy4.pdf

Comparative Analysis of the Complete Chloroplast Genomes of Five Quercus Species

Geraniaceae plastid genomes are highly rearranged, and each of the four genera already sequenced in the family has a distinct genome organization. This study reports plastid genome sequences of six additional species, Francoa sonchifolia, Melianthus villosus, and Viviania marifolia from Geraniales, and Pelargonium alternans, California macrophylla, and Hypseocharis bilobata from Geraniaceae. These genome sequences, combined with previously published species, provide sufficient taxon sampling to reconstruct the ancestral plastid genome organization of Geraniaceae and the rearrangements unique to each genus. The ancestral plastid genome of Geraniaceae has a 4 kb inversion and a reduced, Pelargonium-like small single copy region. Our ancestral genome reconstruction suggests that a few minor rearrangements occurred in the stem branch of Geraniaceae followed by independent rearrangements in each genus. The genomic comparison demonstrates that a series of inverted repeat boundary shifts and inversions played a major role in shaping genome organization in the family. The distribution of repeats is strongly associated with breakpoints in the rearranged genomes, and the proportion and the number of large repeats (>20 bp and >60 bp) are significantly correlated with the degree of genome rearrangements. Increases in the degree of plastid genome rearrangements are correlated with the acceleration in nonsynonymous substitution rates (dN) but not with synonymous substitution rates (dS). Possible mechanisms that might contribute to this correlation, including DNA repair system and selection, are discussed.

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Reconstruction of the Ancestral Plastid Genome in Geraniaceae Reveals a Correlation between Genome Rearrangements, Repeats, and Nucleotide Substitution Rates

Madhumita Govindu

Papers

Reconstruction of the Ancestral Plastid Genome in Geraniaceae Reveals a Correlation between Genome Rearrangements, Repeats, and Nucleotide Substitution Rates

Variable presence of the inverted repeat and plastome stability in Erodium.