For species with minor inverted repeat (IR) boundary changes in the plastid genome (plastome), nucleotide substitution rates were previously shown to be lower in the IR than the single copy regions ...(SC). However, the impact of large-scale IR expansion/contraction on plastid nucleotide substitution rates among closely related species remains unclear.
We included plastomes from 22 Pelargonium species, including eight newly sequenced genomes, and used both pairwise and model-based comparisons to investigate the impact of the IR on sequence evolution in plastids.
Ten types of plastome organization with different inversions or IR boundary changes were identified in Pelargonium. Inclusion in the IR was not sufficient to explain the variation of nucleotide substitution rates. Instead, the rate heterogeneity in Pelargonium plastomes was a mixture of locus-specific, lineage-specific and IR-dependent effects.
Our study of Pelargonium plastomes that vary in IR length and gene content demonstrates that the evolutionary consequences of retaining these repeats are more complicated than previously suggested.
The interest in producing pharmaceutical proteins in a nontoxic plant host has led to the development of an approach to express such proteins in transplastomic lettuce (Lactuca sativa). A number of ...therapeutic proteins and vaccine antigen candidates have been stably integrated into the lettuce plastid genome using biolistic DNA delivery. High levels of accumulation and retention of biological activity suggest that lettuce may provide and ideal platform for the production of biopharmaceuticals.
The plastid genomes of flowering plants Ruhlman, Tracey A; Jansen, Robert K
Methods in molecular biology (Clifton, N.J.),
2014, Volume:
1132
Journal Article
The plastid genome (plastome) has proved a valuable source of data for evaluating evolutionary relationships among angiosperms. Through basic and applied approaches, plastid transformation technology ...offers the potential to understand and improve plant productivity, providing food, fiber, energy and medicines to meet the needs of a burgeoning global population. The growing genomic resources available to both phylogenetic and biotechnological investigations are allowing novel insights and expanding the scope of plastome research to encompass new species. In this chapter we present an overview of some of the seminal and contemporary research that has contributed to our current understanding of plastome evolution and attempt to highlight the relationship between evolutionary mechanisms and tools of plastid genetic engineering.
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•Eleocharis and Cyperaceae have accelerated substitution rates in plastid and mitochondrial genomes with lineage- and gene-specific patterns.•Both synonymous (dS) and nonsynoymous ...(dN) substitution rates are highly accelerated on the branch leading to Cyperaceae compared to most sampled angiosperms.•Cyperaceae organelle genomes show dynamic evolution of gene and intron content.•Mutagenic retroprocessing was supported as one of the most likely drivers for rate accelerations in organelle genomes.
Cyperaceae, the second largest family in the monocot order Poales, comprises >5500 species and includes the genus Eleocharis with ∼ 250 species. A previous study of complete plastomes of two Eleocharis species documented extensive structural heteroplasmy, gene order changes, high frequency of dispersed repeats along with gene losses and duplications. To better understand the phylogenetic distribution of gene and intron content as well as rates and patterns of sequence evolution within and between mitochondrial and plastid genomes of Eleocharis and Cyperaceae, an additional 29 Eleocharis organelle genomes were sequenced and analyzed. Eleocharis experienced extensive gene loss in both genomes while loss of introns was mitochondria-specific. Eleocharis has higher rates of synonymous (dS) and nonsynonymous (dN) substitutions in the plastid and mitochondrion than most sampled angiosperms, and the pattern was distinct from other eudicot lineages with accelerated rates. Several clades showed higher dS and dN in mitochondrial genes than in plastid genes. Furthermore, nucleotide substitution rates of mitochondrial genes were significantly accelerated on the branch leading to Cyperaceae compared to most angiosperms. Mitochondrial genes of Cyperaceae exhibited dramatic loss of RNA editing sites and a negative correlation between RNA editing and dS values was detected among angiosperms. Mutagenic retroprocessing and dysfunction of DNA replication, repair and recombination genes are the most likely cause of striking rate accelerations and loss of edit sites and introns in Eleocharis and Cyperaceae organelle genomes.
PREMISE OF THE STUDY:
There is a misinterpretation in the literature regarding the variable orientation of the small single copy region of plastid genomes (plastomes). The common phenomenon of small ...and large single copy inversion, hypothesized to occur through intramolecular recombination between inverted repeats (IR) in a circular, single unit‐genome, in fact, more likely occurs through recombination‐dependent replication (RDR) of linear plastome templates. If RDR can be primed through both intra‐ and intermolecular recombination, then this mechanism could not only create inversion isomers of so‐called single copy regions, but also an array of alternative sequence arrangements.
METHODS:
We used Illumina paired‐end and PacBio single‐molecule real‐time (SMRT) sequences to characterize repeat structure in the plastome of Monsonia emarginata (Geraniaceae). We used OrgConv and inspected nucleotide alignments to infer ancestral nucleotides and identify gene conversion among repeats and mapped long (>1 kb) SMRT reads against the unit‐genome assembly to identify alternative sequence arrangements.
RESULTS:
Although M. emarginata lacks the canonical IR, we found that large repeats (>1 kilobase; kb) represent ∼22% of the plastome nucleotide content. Among the largest repeats (>2 kb), we identified GC‐biased gene conversion and mapping filtered, long SMRT reads to the M. emarginata unit‐genome assembly revealed alternative, substoichiometric sequence arrangements.
CONCLUSION:
We offer a model based on RDR and gene conversion between long repeated sequences in the M. emarginata plastome and provide support that both intra‐and intermolecular recombination between large repeats, particularly in repeat‐rich plastomes, varies unit‐genome structure while homogenizing the nucleotide sequence of repeats.
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•Ten most phylogenetically informative genes produced a strongly supported phylogeny.•Extensive plastome rearrangements were detected some of which occurred multiple times.•Protein ...coding plastid genes show lineage- and gene-specific rate heterogeneity.•Passiflora shares features present in angiosperms with highly rearranged plastomes.
Plastid genomes (plastomes) of photosynthetic angiosperms are for the most part highly conserved in their organization, mode of inheritance and rates of nucleotide substitution. A small number of distantly related lineages share a syndrome of features that deviate from this general pattern, including extensive genomic rearrangements, accelerated rates of nucleotide substitution, biparental inheritance and plastome-genome incompatibility. Previous studies of plastomes in Passiflora with limited taxon sampling suggested that the genus exhibits this syndrome. To examine this phenomenon further, 15 new plastomes from Passiflora were sequenced and combined with previously published data to examine the phylogenetic relationships, genome organization and evolutionary rates across all five subgenera and the sister genus Adenia. Phylogenomic analyses using 68 protein-coding genes shared by Passiflora generated a fully resolved and strongly supported tree that is congruent with previous phylogenies based on a few plastid and nuclear loci. This phylogeny was used to examine the distribution of plastome rearrangements across Passiflora. Multiple gene and intron losses and inversions were identified in Passiflora with some occurring in parallel and others that extended across the Passifloraceae. Furthermore, extensive expansions and contractions of the inverted repeat (IR) were uncovered and in some cases this resulted in exclusion of all ribosomal RNA genes from the IR. The most highly rearranged lineage was subgenus Decaloba, which experienced extensive IR expansion that incorporated up to 25 protein-coding genes usually located in large single copy region. Nucleotide substitution rate analyses of 68 protein-coding genes across the genus showed lineage- and locus-specific acceleration. Significant increase in dS, dN and dN/dS was detected for clpP across the genus and for ycf4 in certain lineages. Significant increases in dN and dN/dS for ribosomal subunits and plastid-encoded RNA polymerase genes were detected in the branch leading to the expanded IR-clade in subgenus Decaloba. This subgenus displays the syndrome of unusual features, making it an ideal system to investigate the dynamic evolution of angiosperm plastomes.
The exchange of genetic material between cellular organelles through intracellular gene transfer (IGT) or between species by horizontal gene transfer (HGT) has played an important role in plant ...mitochondrial genome evolution. The mitochondrial genomes of Geraniaceae display a number of unusual phenomena including highly accelerated rates of synonymous substitutions, extensive gene loss and reduction in RNA editing.
Mitochondrial DNA sequences assembled for 17 species of Geranium revealed substantial reduction in gene and intron content relative to the ancestor of the Geranium lineage. Comparative analyses of nuclear transcriptome data suggest that a number of these sequences have been functionally relocated to the nucleus via IGT.
Evidence for rampant HGT was detected in several Geranium species containing foreign organellar DNA from diverse eudicots, including many transfers from parasitic plants. One lineage has experienced multiple, independent HGT episodes, many of which occurred within the past 5.5 Myr.
Both duplicative and recapture HGT were documented in Geranium lineages. The mitochondrial genome of Geranium brycei contains at least four independent HGT tracts that are absent in its nearest relative. Furthermore, G. brycei mitochondria carry two copies of the cox1 gene that differ in intron content, providing insight into contrasting hypotheses on cox1 intron evolution.
The genus
is the largest of the tribe Trifolieae in the subfamily Papilionoideae (Fabaceae). The paucity of mitochondrial genome (mitogenome) sequences has hindered comparative analyses among the ...three genomic compartments of the plant cell (nucleus, mitochondrion and plastid). We assembled four mitogenomes from the two subgenera (
and
) of the genus. The four
mitogenomes were compact (294,911-348,724 bp in length) and contained limited repetitive (6.6-8.6%) DNA. Comparison of organelle repeat content highlighted the distinct evolutionary trajectory of plastid genomes in a subset of
species. Intracellular gene transfer (IGT) was analyzed among the three genomic compartments revealing functional transfer of mitochondrial
to nuclear genome along with other IGT events. Phylogenetic analysis based on mitochondrial and nuclear
sequences revealed that the functional transfer in Trifolieae was independent from the event that occurred in robinioid clade that includes genus
. A novel, independent fission event of
in
was identified, caused by a 59 bp deletion. Fissions of this gene reported previously in land plants were reassessed and compared with
.
Barley is characterized by a rich genetic diversity, making it an important model for studies of salinity response with great potential for crop improvement. Moreover, salt stress severely affects ...barley growth and development, leading to substantial yield loss. Leaf and root transcriptomes of a salt-tolerant Tunisian landrace (Boulifa) exposed to 2, 8, and 24 h salt stress were compared with pre-exposure plants to identify candidate genes and pathways underlying barley's response. Expression of 3585 genes was upregulated and 5586 downregulated in leaves, while expression of 13,200 genes was upregulated and 10,575 downregulated in roots. Regulation of gene expression was severely impacted in roots, highlighting the complexity of salt stress response mechanisms in this tissue. Functional analyses in both tissues indicated that response to salt stress is mainly achieved through sensing and signaling pathways, strong transcriptional reprograming, hormone osmolyte and ion homeostasis stabilization, increased reactive oxygen scavenging, and activation of transport and photosynthesis systems. A number of candidate genes involved in hormone and kinase signaling pathways, as well as several transcription factor families and transporters, were identified. This study provides valuable information on early salt-stress-responsive genes in roots and leaves of barley and identifies several important players in salt tolerance.
Comprising 501 genera and around 14,000 species, Papilionoideae is not only the largest subfamily of Fabaceae (Leguminosae; legumes), but also one of the most extraordinarily diverse clades among ...angiosperms. Papilionoids are a major source of food and forage, are ecologically successful in all major biomes, and display dramatic variation in both floral architecture and plastid genome (plastome) structure. Plastid DNA-based phylogenetic analyses have greatly improved our understanding of relationships among the major groups of Papilionoideae, yet the backbone of the subfamily phylogeny remains unresolved. In this study, we sequenced and assembled 39 new plastomes that are covering key genera representing the morphological diversity in the subfamily. From 244 total taxa, we produced eight datasets for maximum likelihood (ML) analyses based on entire plastomes and/or concatenated sequences of 77 protein-coding sequences (CDS) and two datasets for multispecies coalescent (MSC) analyses based on individual gene trees. We additionally produced a combined nucleotide dataset comprising CDS plus
gene sequences only, in which most papilionoid genera were sampled. A ML tree based on the entire plastome maximally supported all of the deep and most recent divergences of papilionoids (223 out of 236 nodes). The Swartzieae, ADA (Angylocalyceae, Dipterygeae, and Amburaneae), Cladrastis, Andira, and Exostyleae clades formed a grade to the remainder of the Papilionoideae, concordant with nine ML and two MSC trees. Phylogenetic relationships among the remaining five papilionoid lineages (Vataireoid,
, Genistoid s.l., Dalbergioid s.l., and Baphieae + Non-Protein Amino Acid Accumulating or NPAAA clade) remained uncertain, because of insufficient support and/or conflicting relationships among trees. Our study fully resolved most of the deep nodes of Papilionoideae, however, some relationships require further exploration. More genome-scale data and rigorous analyses are needed to disentangle phylogenetic relationships among the five remaining lineages.
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