Search

Bacterial soft rot is a devastating disease for a wide range of crops, vegetables, and ornamental plants including konjac (Amorphophallus konjac). However, the pangenome and genomic plasticity of the konjac soft rot pathogens is little explored. In this study, we reported the complete genome sequences of 11 bacterial isolates that can cause typical soft rot symptoms in konjac by in vitro and in vivo pathogenicity tests. Based on in silico DNA-DNA hybridization, average nucleotide identity and phylogenomic analysis, all 11 isolates were determined to be Pectobacterium aroidearum. In addition, synteny analysis of these genomes revealed considerable chromosomal inversions, one of which is triggered by homologous recombination of ribose operon. Pangenome analysis and COG enrichment analysis showed that the pangenome of P. aroidearum is open and that accessory genes are enriched in replication, recombination, and repair. Variations in type IV secretion system and type VI secretion system were found, while plant cell wall degrading enzymes were conserved. Furthermore, sequence analyses also provided evidence for the presence of a type V secretion system in Pectobacterium. These findings advance our understanding of the pathogenicity determinants, genomic plasticity, and evolution of P. aroidearum. [ABSTRACT FROM AUTHOR]

The azoospermia factor c region (AZFc), located in the long arm of the human Y chromosome, is frequently involved in chromosome rearrangements, mainly due to non-allelic homologous recombination events that occur between the nearly identical sequences (amplicon) that comprises it. These rearrangements may have major phenotypic effects like spermatogenic failure or other pathologies linked to male infertility. Moreover, they may also be relevant in forensic genetics, since some of the Y chromosome short tandem repeats (Y-STRs) commonly used in forensic analysis are located in amplicons or in inter-amplicon sequences of the AZFc. In a previous study, we identified four phylogenetically related samples with a null allele at DYS448 and a tetrallelic pattern at DYF387S1, two Y-STRs located in the AZFc. Through NGS read depth analysis, we found that the unusual Y-STR pattern may be due to a 1.6 Mb deletion arising concurrently or after a 3.5 Mb duplication event. The observed large genomic rearrangement results in copy number reduction for the RBMY gene family as well as duplication of other AZFc genes. Based on the diversity of 16 additional Y-STRs, we estimated that the duplication/deletion event occurred at least twenty generations ago, suggesting that it has not been affected by negative selection.

The azoospermia factor c region (AZFc), located in the long arm of the human Y chromosome, is frequently involved in chromosome rearrangements, mainly due to non-allelic homologous recombination events that occur between the nearly identical sequences (amplicon) that comprises it. These rearrangements may have major phenotypic effects like spermatogenic failure or other pathologies linked to male infertility. Moreover, they may also be relevant in forensic genetics, since some of the Y chromosome short tandem repeats (Y-STRs) commonly used in forensic analysis are located in amplicons or in inter-amplicon sequences of the AZFc. In a previous study, we identified four phylogenetically related samples with a null allele at DYS448 and a tetrallelic pattern at DYF387S1, two Y-STRs located in the AZFc. Through NGS read depth analysis, we found that the unusual Y-STR pattern may be due to a 1.6 Mb deletion arising concurrently or after a 3.5 Mb duplication event. The observed large genomic rearrangement results in copy number reduction for the RBMY gene family as well as duplication of other AZFc genes. Based on the diversity of 16 additional Y-STRs, we estimated that the duplication/deletion event occurred at least twenty generations ago, suggesting that it has not been affected by negative selection. [ABSTRACT FROM AUTHOR]

The typical plastid genome (plastome) of photosynthetic angiosperms comprises a pair of Inverted Repeat regions (IRs), which separate a Large Single Copy region (LSC) from a Small Single Copy region (SSC). The independent losses of IRs have been documented in only a few distinct plant lineages. The majority of these taxa show uncommonly high levels of plastome structural variations, while a few have otherwise conserved plastomes. For a better understanding of the function of IRs in stabilizing plastome structure, more taxa that have lost IRs need to be investigated. We analyzed the plastomes of eight species from two genera of the putranjivoid clade of Malpighiales using Illumina paired-end sequencing, the de novo assembly strategy GetOrganelle, as well as a combination of two annotation methods. We found that all eight plastomes of the putranjivoid clade have lost their IRB, representing the fifth case of IR loss within autotrophic angiosperms. Coinciding with the loss of the IR, plastomes of the putranjivoid clade have experienced significant structural variations including gene and intron losses, multiple large inversions, as well as the translocation and duplication of plastome segments. However, Balanopaceae, one of the close relatives of the putranjivoid clade, exhibit a relatively conserved plastome organization with canonical IRs. Our results corroborate earlier reports that the IR loss and additional structural reorganizations are closely linked, hinting at a shared mechanism that underpins structural disturbances.

Small supernumerary marker chromosomes (SMCs) are rare cytogenetic abnormalities. De novo small SMCs, particularly those combined with uniparental disomy (UPD), are assumed to result from incomplete trisomy rescue. Recently, a one-off cellular event designated as chromothripsis was reported as a mechanism for trisomy rescue in micronuclei. This Perspective article aims to highlight a possible association among trisomy rescue, chromothripsis, and SMCs. We propose that chromothripsis-mediated incomplete trisomy rescue in micronuclei underlies various chromosomal rearrangements including SMCs, although other mechanisms such as U-type exchange may also yield SMCs. These assumptions are primarily based on observations of previously reported patients with complex rearrangements and our patient with a small SMC. Given the high frequency of trisomic cells in human preimplantation embryos, chromothripsis-mediated trisomy rescue may be a physiologically important phenomenon. Nevertheless, trisomy rescue has a potential to produce UPD, SMCs, and other chromosomal rearrangements. The concepts of trisomy rescue, chromothripsis, and micronuclei provide novel insights into the mechanism for the maintenance and modification of human chromosomes.

Recombinant strains of hepatitis E virus (HEV) with insertions of human genomic fragments or HEV sequence duplications in the sequence encoding the polyproline region (PPR) were previously described in chronically infected patients. Such genomic rearrangements confer a replicative advantage in vitro but little is known about their frequency, location, or origin. As the sequences of only a few virus genomes are available, we analyzed the complete genomes of 114 HEV genotype 3 strains from immunocompromised (n = 85) and immunocompetent (n = 29) patients using the single molecular real-time sequencing method to determine the frequency, location, and origin of inserted genomic fragments, plus the proportions of variants with genomic rearrangements in each virus quasispecies. We also examined the amino acid compositions and post-translational modifications conferred by these rearrangements by comparing them to sequences without human gene insertions or HEV gene duplications. We found genomic rearrangements in 7/114 (6.1%) complete genome sequences (4 HEV-3f, 1 HEV-3e, 1 HEV-3 h, and 1 HEV-3chi-new), all from immunocompromised patients, and 3/7 were found at the acute phase of infection. Six of the seven patients harbored virus-host recombinant variants, including one patient with two different recombinant variants. We also detected three recombinant variants with genome duplications of the PPR or PPR + X domains in a single patient. All the genomic rearrangements (seven human fragment insertions of varying origins and three HEV genome duplications) occurred in the PPR. The sequences with genomic rearrangements had specific characteristics: increased net load (p < 0.001) and more ubiquitination (p < 0.001), phosphorylation (p < 0.001), and acetylation (p < 0.001) sites. The human fragment insertions and HEV genome duplications had slightly different characteristics. We believe this is the first description of HEV strains with genomic rearrangements in patients at the acute phase of infection; perhaps these strains are directly transmitted. Clearly, genomic rearrangements produce a greater net load with duplications and insertions having different features. Further studies are needed to clarify the mechanisms by which such modifications influence HEV replication.

The typical plastid genome (plastome) of photosynthetic angiosperms comprises a pair of Inverted Repeat regions (IRs), which separate a Large Single Copy region (LSC) from a Small Single Copy region (SSC). The independent losses of IRs have been documented in only a few distinct plant lineages. The majority of these taxa show uncommonly high levels of plastome structural variations, while a few have otherwise conserved plastomes. For a better understanding of the function of IRs in stabilizing plastome structure, more taxa that have lost IRs need to be investigated. We analyzed the plastomes of eight species from two genera of the putranjivoid clade of Malpighiales using Illumina paired-end sequencing, the de novo assembly strategy GetOrganelle, as well as a combination of two annotation methods. We found that all eight plastomes of the putranjivoid clade have lost their IRB, representing the fifth case of IR loss within autotrophic angiosperms. Coinciding with the loss of the IR, plastomes of the putranjivoid clade have experienced significant structural variations including gene and intron losses, multiple large inversions, as well as the translocation and duplication of plastome segments. However, Balanopaceae, one of the close relatives of the putranjivoid clade, exhibit a relatively conserved plastome organization with canonical IRs. Our results corroborate earlier reports that the IR loss and additional structural reorganizations are closely linked, hinting at a shared mechanism that underpins structural disturbances. [ABSTRACT FROM AUTHOR]

Small supernumerary marker chromosomes (SMCs) are rare cytogenetic abnormalities. De novo small SMCs, particularly those combined with uniparental disomy (UPD), are assumed to result from incomplete trisomy rescue. Recently, a one-off cellular event designated as chromothripsis was reported as a mechanism for trisomy rescue in micronuclei. This Perspective article aims to highlight a possible association among trisomy rescue, chromothripsis, and SMCs. We propose that chromothripsis-mediated incomplete trisomy rescue in micronuclei underlies various chromosomal rearrangements including SMCs, although other mechanisms such as U-type exchange may also yield SMCs. These assumptions are primarily based on observations of previously reported patients with complex rearrangements and our patient with a small SMC. Given the high frequency of trisomic cells in human preimplantation embryos, chromothripsis-mediated trisomy rescue may be a physiologically important phenomenon. Nevertheless, trisomy rescue has a potential to produce UPD, SMCs, and other chromosomal rearrangements. The concepts of trisomy rescue, chromothripsis, and micronuclei provide novel insights into the mechanism for the maintenance and modification of human chromosomes. [ABSTRACT FROM AUTHOR]

Recombinant strains of hepatitis E virus (HEV) with insertions of human genomic fragments or HEV sequence duplications in the sequence encoding the polyproline region (PPR) were previously described in chronically infected patients. Such genomic rearrangements confer a replicative advantage in vitro but little is known about their frequency, location, or origin. As the sequences of only a few virus genomes are available, we analyzed the complete genomes of 114 HEV genotype 3 strains from immunocompromised (n = 85) and immunocompetent (n = 29) patients using the single molecular real-time sequencing method to determine the frequency, location, and origin of inserted genomic fragments, plus the proportions of variants with genomic rearrangements in each virus quasispecies. We also examined the amino acid compositions and post-translational modifications conferred by these rearrangements by comparing them to sequences without human gene insertions or HEV gene duplications. We found genomic rearrangements in 7/114 (6.1%) complete genome sequences (4 HEV-3f, 1 HEV-3e, 1 HEV-3 h, and 1 HEV-3chi-new), all from immunocompromised patients, and 3/7 were found at the acute phase of infection. Six of the seven patients harbored virus-host recombinant variants, including one patient with two different recombinant variants. We also detected three recombinant variants with genome duplications of the PPR or PPR + X domains in a single patient. All the genomic rearrangements (seven human fragment insertions of varying origins and three HEV genome duplications) occurred in the PPR. The sequences with genomic rearrangements had specific characteristics: increased net load (p < 0.001) and more ubiquitination (p < 0.001), phosphorylation (p < 0.001), and acetylation (p < 0.001) sites. The human fragment insertions and HEV genome duplications had slightly different characteristics. We believe this is the first description of HEV strains with genomic rearrangements in patients at the acute phase of infection; perhaps these strains are directly transmitted. Clearly, genomic rearrangements produce a greater net load with duplications and insertions having different features. Further studies are needed to clarify the mechanisms by which such modifications influence HEV replication. [ABSTRACT FROM AUTHOR]

The factors behind genome size evolution have been of great interest, considering that eukaryotic genomes vary in size by more than three orders of magnitude. Using a model of two wild peanut relatives, Arachis duranensis and Arachis ipaensis, in which one genome experienced large rearrangements, we find that the main determinant in genome size reduction is a set of inversions that occurred in A. duranensis, and subsequent net sequence removal in the inverted regions. We observe a general pattern in which sequence is lost more rapidly at newly distal (telomeric) regions than it is gained at newly proximal (pericentromeric) regions – resulting in net sequence loss in the inverted regions. The major driver of this process is recombination, determined by the chromosomal location. Any type of genomic rearrangement that exposes proximal regions to higher recombination rates can cause genome size reduction by this mechanism. In comparisons between A. duranensis and A. ipaensis, we find that the inversions all occurred in A. duranensis. Sequence loss in those regions was primarily due to removal of transposable elements. Illegitimate recombination is likely the major mechanism responsible for the sequence removal, rather than unequal intrastrand recombination. We also measure the relative rate of genome size reduction in these two Arachis diploids. We also test our model in other plant species and find that it applies in all cases examined, suggesting our model is widely applicable.

The factors behind genome size evolution have been of great interest, considering that eukaryotic genomes vary in size by more than three orders of magnitude. Using a model of two wild peanut relatives, Arachis duranensis and Arachis ipaensis , in which one genome experienced large rearrangements, we find that the main determinant in genome size reduction is a set of inversions that occurred in A. duranensis , and subsequent net sequence removal in the inverted regions. We observe a general pattern in which sequence is lost more rapidly at newly distal (telomeric) regions than it is gained at newly proximal (pericentromeric) regions – resulting in net sequence loss in the inverted regions. The major driver of this process is recombination, determined by the chromosomal location. Any type of genomic rearrangement that exposes proximal regions to higher recombination rates can cause genome size reduction by this mechanism. In comparisons between A. duranensis and A. ipaensis , we find that the inversions all occurred in A. duranensis. Sequence loss in those regions was primarily due to removal of transposable elements. Illegitimate recombination is likely the major mechanism responsible for the sequence removal, rather than unequal intrastrand recombination. We also measure the relative rate of genome size reduction in these two Arachis diploids. We also test our model in other plant species and find that it applies in all cases examined, suggesting our model is widely applicable. [ABSTRACT FROM AUTHOR]

Episodic ataxia (EA) syndromes are heritable diseases characterized by dramatic episodes of imbalance and incoordination. Episodic ataxia type 2 (EA2), the most common and the best characterized subtype, is caused by mostly nonsense, splice site, small indel and sometimes missense mutations in CACNA1A. Direct sequencing of CACNA1A fails to identify mutations in some patients with EA2-like features, possibly due to incomplete interrogation of CACNA1A or defects in other EA genes not yet defined. Previous reports described genomic deletions between 4-40kb in EA2. In 47 subjects with EA (26 with EA2-like features) who tested negative for mutations in the known EA genes, we used Multiplex Ligation-dependent Probe Amplification (MLPA) to analyze CACNA1A for exonic copy number variations. Breakpoints were further defined by long-range PCR. We identified distinct multi-exonic deletions in three probands with classic EA2-like features: episodes of prolonged vertigo and ataxia triggered by stress and fatigue, interictal nystagmus, with onset during infancy or early childhood. The breakpoints in all three probands are located in Alu sequences, indicating errors in homologous recombination of Alu sequences as the underlying mechanism. The smallest deletion spanned exons 39 and 40, while the largest deletion spanned 200kb, missing all but the first three exons. One deletion involving exons 39 through 47 arose spontaneously. The search for mutations in CACNA1A appears most fruitful in EA patients with interictal nystagmus and onset early in life. The finding of large heterozygous deletions suggests haploinsufficiency as a possible pathomechanism of EA2.