Amplicon melting analysis with labeled primers: a closed-tube method for differentiating homozygotes and heterozygotes

Factors influencing false-positive results of rifampicin resistance detected by Xpert MTB/RIF: A retrospective study in Zhejiang, China

Objective

This study aimed to explore the factors influencing false-positive results for rifampicin resistance (RIF-R) detected using Xpert MTB/RIF (Xpert).

Methods

This retrospective analysis included the clinical data of patients from September 2019 to February 2023. The chi-square and rank sum tests were used to compare differences in patient characteristics between the true-positive and false-positive groups. Logistic regression was used to analyze the factors influencing false positives in the detection of RIF-R by Xpert.

Results

A total of 384 patients were included. Logistic regression analysis revealed that, with mutation of probe E as the reference, mutations on probe A or C (OR = 72.68, P < 0.001), probe D (OR = 6.44, P < 0.001), and multiple probes (OR = 5.94, P = 0.002) were associated with false-positive results in Xpert detection of RIF-R. Taking probe delay ΔCt <4 as the reference, ΔCt (4-5.9) (OR = 13.54, P < 0.001), ΔCt (6-7.9) (OR = 48.08, P < 0.001) probe delays were associated with false positives in Xpert detection of RIF-R. When very low quantification is accompanied by a probe delay, the probability of false-positive RIF-R detection can reach 80 %.

Conclusions

Clinicians should consider factors such as probe mutation type, probe delay, and very low quantification accompanied by probe delay when interpreting Xpert results, which can reduce the misdiagnosis of tuberculosis drug resistance.

DNA melting analysis

Melting is a fundamental property of DNA that can be monitored by absorbance or fluorescence. PCR conveniently produces enough DNA to be directly monitored on real-time instruments with fluorescently labeled probes or dyes. Dyes monitor the entire PCR product, while probes focus on a specific locus within the amplicon. Advances in amplicon melting include high resolution instruments, saturating DNA dyes that better reveal multiple products, prediction programs for domain melting, barcode taxonomic identification, high speed microfluidic melting, and highly parallel digital melting. Most single base variants and small insertions or deletions can be genotyped by high resolution amplicon melting. High resolution melting also enables heterozygote scanning for any variant within a PCR product. A web application (uMelt, http://www.dna-utah.org) predicts amplicon melting curves with multiple domains, a useful tool for verifying intended products. Additional applications include methylation assessment, copy number determination and verification of sequence identity. When amplicon melting does not provide sufficient detail, unlabeled probes or snapback primers can be used instead of covalently labeled probes. DNA melting is a simple, inexpensive, and powerful tool with many research applications that is beginning to make its mark in clinical diagnostics.

[Sperm Mosaic Variants and Their Influence on the Offspring]

Genomic mosaicism arising from mosaic variants is a phenomenon that describes the presence of a cell or cell populations with different genome compositions from the germline cells of an individual. It comprises all types of genetic variants. A large proportion of childhood genetic disorders are defined as being de novo, meaning that the disease-causing mutations are only detected in the proband, not in any of the parents. Population studies show that 80% of the de novo mutations arise from the paternal haplotype, that is, from paternal sperm mosaicism. This review provides a summary of the types and detection strategies of sperm mosaicism. In addition, it provides discussions on how recent studies demonstrated that genomic mosaic mutations in parents, especially those in the paternal sperms, could be inherited by the offspring and cause childhood disorders. According to the previous findings of the author's research team, sperm mosaicism derived from early embryogenesis and primordial germ cell stages can explain 5% to 20% of the de novo mutations related to clinical phenotypes and can serve as an important predictor of both rare and complex disorders. Sperm mosaicism shows great potential for clinical genetic diagnosis and consultations. Based on the published literature, the author suggests that, large-scale screening for de novo sperm mosaic mutations and population-based genetic screening should be conducted in future studies, which will greatly enhance the risk assessment in the offspring and effectively improve the genetic health at the population level. Implementation of direct sperm detection for de novo mutations will significantly increase the efficiency of the stratification of patient cohorts and improve recurrence risk assessment for future births. Future research in the field should be focused on the impact of environmental and lifestyle factors on the health of the offspring through sperms and their modeling of mutation signatures. In addition, targeted in vitro modeling of sperm mutations will also be a promising direction.

Is it the end of TILLING era in plant science?

Since its introduction in 2000, the TILLING strategy has been widely used in plant research to create novel genetic diversity. TILLING is based on chemical or physical mutagenesis followed by the rapid identification of mutations within genes of interest. TILLING mutants may be used for functional analysis of genes and being nontransgenic, they may be directly used in pre-breeding programs. Nevertheless, classical mutagenesis is a random process, giving rise to mutations all over the genome. Therefore TILLING mutants carry background mutations, some of which may affect the phenotype and should be eliminated, which is often time-consuming. Recently, new strategies of targeted genome editing, including CRISPR/Cas9-based methods, have been developed and optimized for many plant species. These methods precisely target only genes of interest and produce very few off-targets. Thus, the question arises: is it the end of TILLING era in plant studies? In this review, we recap the basics of the TILLING strategy, summarize the current status of plant TILLING research and present recent TILLING achievements. Based on these reports, we conclude that TILLING still plays an important role in plant research as a valuable tool for generating genetic variation for genomics and breeding projects.

A duplex tetra-primer ARMS-PCR assay to discriminate three species of the Schistosoma haematobium group: Schistosoma curassoni, S. bovis, S. haematobium and their hybrids

BACKGROUND

The use of applications involving single nucleotide polymorphisms (SNPs) has greatly increased since the beginning of the 2000s, with the number of associated techniques expanding rapidly in the field of molecular research. Tetra-primer amplification refractory mutation system-PCR (T-ARMS-PCR) is one such technique involving SNP genotyping. It has the advantage of amplifying multiple alleles in a single reaction with the inclusion of an internal molecular control. We report here the development of a rapid, reliable and cost-effective duplex T-ARMS-PCR assay to distinguish between three Schistosoma species, namely Schistosoma haematobium (human parasite), Schistosoma bovis and Schistosoma curassoni (animal parasites), and their hybrids. This technique will facilitate studies of population genetics and the evolution of introgression events.

METHODS

During the development of the technique we focused on one of the five inter-species internal transcribed spacer (ITS) SNPs and one of the inter-species 18S SNPs which, when combined, discriminate between all three Schistosoma species and their hybrid forms. We designed T-ARMS-PCR primers to amplify amplicons of specific lengths for each species, which in turn can then be visualized on an electrophoresis gel. This was further tested using laboratory and field-collected adult worms and field-collected larval stages (miracidia) from Spain, Egypt, Mali, Senegal and Ivory Coast. The combined duplex T-ARMS-PCR and ITS + 18S primer set was then used to differentiate the three species in a single reaction.

RESULTS

The T-ARMS-PCR assay was able to detect DNA from both species being analysed at the maximum and minimum levels in the DNA ratios (95/5) tested. The duplex T-ARMS-PCR assay was also able to detect all hybrids tested and was validated by sequencing the ITS and the 18S amplicons of 148 of the field samples included in the study.

CONCLUSIONS

The duplex tetra-primer ARMS-PCR assay described here can be applied to differentiate between Schistosoma species and their hybrid forms that infect humans and animals, thereby providing a method to investigate the epidemiology of these species in endemic areas. The addition of several markers in a single reaction saves considerable time and is of long-standing interest for investigating genetic populations.

The use of a candidate gene approach to study Botrytis cinerea resistance in Gerbera hybrida

Candidate genes (CG) for Botrytis cinerea resistance described in literature were mapped on gerbera linkage maps for which several QTL for Botrytis resistance had been found previously using a rapid, low-cost platform for SNP genotyping. In total, 29 CGs were mapped in either of two mapping populations. Four CGs were mapped within the previous identified QTL intervals and three co-localized with QTL. Two of these CGs for resistance against B. cinerea, PG1 (polygalacturonase gene) and sit (sitiens, ABA-aldehyde oxidase gene) that mapped in QTL regions for the ray floret disease resistance test were studied in detail. Virus-induced gene silencing (VIGS) was used for gene function analysis to determine the CGs' role in gerbera resistance to Botrytis. Ray florets, of which the CGs were silenced, showed a significantly delayed growth of lesions upon Botrytis infection compared to controls. Combining QTL analysis, candidate gene mapping and VIGS showed to be an useful combination to identify possible causal genes and for understanding the molecular mechanisms of Botrytis resistance in gerbera. The two genes seem to act as partial S-genes and are likely among the determining genes leading to the variation observed for B. cinerea resistance in gerbera.

High-Resolution Melting (HRM) Genotyping

High-resolution melting (HRM) analysis is a simple, fast, and inexpensive real-time polymerase chain reaction (PCR)-based method used to identify genetic variation between populations and detect single-nucleotide polymorphisms (SNPs) in nucleic acid sequences. HRM is a powerful technique that detects the differences between SNP allele melting temperatures by using a fluorescent dye inserted into the duplex deoxyribonucleic acid (DNA) structure. Prior to performing HRM analysis, optimizing the primer design, PCR mixture, and software settings is essential to obtain accurate and reliable results. In this chapter, we describe a detailed SNP genotyping method that includes primer design and the analysis of the shapes and positions of the melt curve of the luminescence intensity of the fluorescent dye attached to amplified DNA using software of qPCR instruments. This protocol is applicable for genotyping germplasm, genetic mapping, and marker-assisted breeding in plants.

Accurate, fast and cost-effective simultaneous detection of bacterial meningitis by qualitative PCR with high-resolution melting

Neisseria meningitidis, Haemophilus influenzae and Streptococcus pneumoniae are leading causes of meningitis and acute invasive infections. PCR-based methods are widely used for the diagnosis and surveillance of bacterial pathogens because of their high sensitivity, specificity and high-throughput capabilities compared with conventional laboratory methods. This study evaluated a high-resolution melting qualitative PCR analysis method for the simultaneous detection of these three pathogens. The assay has been optimized to detect three species-specific genes of each organism isolated from clinical samples, enabling accurate identification of the etiological agent. The method proved to be highly sensitive and cheaper than the real-time PCR TaqMan^® system because it is probe-free; it could be used for the diagnosis of invasive diseases in public health laboratories of developing countries.

Real-Time PCR High-Resolution Melting Assays for the Detection of Foodborne Pathogens

Real-time PCR high-resolution melting assays are a method for the identification of single nucleotide polymorphisms (SNPs). The assay is performed by amplifying a short DNA fragment using a specific primer pair flanking a target SNP in the presence of a high-resolution melting dye. The HRM analysis of amplicons groups the samples based on the differences in the melting temperature and the shape of the melt curves, facilitating a convenient genotyping of samples. This chapter describes the steps and considerations of real-time PCR HRM assay standardization.

KRAS in NSCLC: State of the Art and Future Perspectives

In NSCLC, KRAS mutations occur in up to 30% of all cases, most frequently at codon 12 and 13. KRAS mutations have been linked to adenocarcinoma histology, positive smoking history, and Caucasian ethnicity, although differences have been described across KRAS mutational variants subtypes. KRAS mutations often concur with other molecular alterations, notably TP53, STK11, and KEAP1, which could play an important role in treatment efficacy and patient outcomes. For many years, KRAS mutations have been considered undruggable mainly due to a high toxicity profile and low specificity of compounds. Sotorasib and adagrasib are novel KRAS inhibitors that recently gained FDA approval for pre-treated KRAS mutant NSCLC patients, and other molecules such as GDC-6036 are currently being investigated with promising results. Despite their approval, the efficacy of these drugs is lower than expected and progression among responders has been reported. Mechanisms of acquired resistance to anti-KRAS molecules typically involves either on target secondary mutations (e.g., G12, G13, Q61H, R68S, H95, Y96C, V8L) or off-target alterations. Ongoing trials are currently evaluating strategies for implementing efficacy and overcoming acquired resistance to these compounds. Finally, the efficacy of immune-checkpoint inhibitors still needs to be completely assessed and responses to anti-PD-1/PD-L1 agents may strongly depend on concomitant mutations.

Universal probe-based intermediate primer-triggered qPCR (UPIP-qPCR) for SNP genotyping

BACKGROUND

The detection and identification of single nucleotide polymorphism (SNP) is essential for determining patient disease susceptibility and the delivery of medicines targeted to the individual. At present, SNP genotyping technology includes Sanger sequencing, TaqMan-probe quantitative polymerase chain reaction (qPCR), amplification-refractory mutation system (ARMS)-PCR, and Kompetitive Allele-Specific PCR (KASP). However, these technologies have some disadvantages: the high cost of development and detection, long and time consuming protocols, and high false positive rates. Focusing on these limitations, we proposed a new SNP detection method named universal probe-based intermediate primer-triggered qPCR (UPIP-qPCR). In this method, only two types of fluorescence-labeled probes were used for SNP genotyping, thus greatly reducing the cost of development and detection for SNP genotyping.

RESULTS

In the amplification process of UPIP-qPCR, unlabeled intermediate primers with template-specific recognition functions could trigger probe hydrolysis and specific signal release. UPIP-qPCR can be used successfully and widely for SNP genotyping. The sensitivity of UPIP-qPCR in SNP genotyping was 0.01 ng, the call rate was more than 99.1%, and the accuracy was more than 99.9%. High-throughput DNA microarrays based on intermediate primers can be used for SNP genotyping.

CONCLUSION

This novel approach is both cost effective and highly accurate; it is a reliable SNP genotyping method that would serve the needs of the clinician in the provision of targeted medicine.

Application of Nanotechnology for Sensitive Detection of Low-Abundance Single-Nucleotide Variations in Genomic DNA: A Review

Single-nucleotide polymorphisms (SNPs) are the simplest and most common type of DNA variations in the human genome. This class of attractive genetic markers, along with point mutations, have been associated with the risk of developing a wide range of diseases, including cancer, cardiovascular diseases, autoimmune diseases, and neurodegenerative diseases. Several existing methods to detect SNPs and mutations in body fluids have faced limitations. Therefore, there is a need to focus on developing noninvasive future polymerase chain reaction (PCR)-free tools to detect low-abundant SNPs in such specimens. The detection of small concentrations of SNPs in the presence of a large background of wild-type genes is the biggest hurdle. Hence, the screening and detection of SNPs need efficient and straightforward strategies. Suitable amplification methods are being explored to avoid high-throughput settings and laborious efforts. Therefore, currently, DNA sensing methods are being explored for the ultrasensitive detection of SNPs based on the concept of nanotechnology. Owing to their small size and improved surface area, nanomaterials hold the extensive capacity to be used as biosensors in the genotyping and highly sensitive recognition of single-base mismatch in the presence of incomparable wild-type DNA fragments. Different nanomaterials have been combined with imaging and sensing techniques and amplification methods to facilitate the less time-consuming and easy detection of SNPs in different diseases. This review aims to highlight some of the most recent findings on the aspects of nanotechnology-based SNP sensing methods used for the specific and ultrasensitive detection of low-concentration SNPs and rare mutations.

Development of a novel, high resolution melting analysis based genotyping method for Cryptosporidium parvum

This study employed the post-real-time PCR application, high resolution melting (HRM) analysis, in order to differentiate between characterised clinical and reference Cryptosporidium parvum samples obtained from Cork University Hospital (Cork, Ireland) and the Cryptosporidium Reference Unit (Swansea, Wales). A sample set composed of 18 distinct C. parvum gp60-subtypes of the IIa gp60-subtype family (an allele family accounting for over 80% of all cryptosporidiosis cases in Ireland) was employed. HRM analysis-based interrogation of the gp60, MM5 and MS9-Mallon tandem repeat loci was found to completely differentiate between 10 of the 18 studied gp60-subtypes. The remaining eight gp60-subtypes were differentiated into three distinct groupings, with the designations within these groupings resolved to two to three potential gp60-subtypes. The current study aimed to develop a novel, reproducible, real-time PCR based multi-locus genotyping method to distinguish between C. parvum gp60-subtypes. These preliminary results support the further expansion of the multi-locus panel in order to increase the discriminatory capabilities of this novel method.

Simultaneous identification of Fritillariae cirrhosae bulbus and its common adulterants in one reaction by multiplex ligation-dependent probe amplification and high-resolution melting curve assay

Fritillariae cirrhosae bulbus, a well-known and precious medicinal and edible herb in China, causes remarkable effects on swelling and relieving cough, with fewer side effects than other congeneric medicine. It has been subject to various cheaper congeneric adulteration because of its high price and limited production. In this paper, a rapid, high throughput, sensitive and efficient technique was described for simultaneous identification of F. cirrhosae bulbus and its common adulterants by employing multiplex ligation-dependent probe amplification coupled with high-resolution melting (MLPA-HRM) curve assay in their internal transcribed spacer 1 (ITS1) regions. This assay was highly sensitive with a detection limit of 0.19 ng genomic DNA, and highly specific with no cross-reaction with common adulterants. Mixed sample analysis showed as low as 10% adulteration can be detected from F. cirrhosae bulbus in one MLPA-HRM reaction. Overall, the method described in this paper is well suited for detecting adulteration in F. cirrhosae bulbus.

Rapid screening of UPB1 gene variations by high resolution melting curve analysis

The present study aimed to analyze gene mutations in patients with β-ureidopropinoase deficiency and establish a rapid detection method for β-ureidopropinoase (UPB1) pathogenic variations by high resolution melting (HRM) analysis. DNA samples with known UPB1 mutations in three patients with β-ureidopropinoase deficiency were utilized to establish a rapid detection method for UPB1 pathogenic variations by HRM analysis. Further rapid screening was performed on two patients diagnosed with β-ureidopropinoase deficiency and 50 healthy control individuals. The results showed that all known UPB1 gene mutations can be analyzed by a specially designed HRM assay. Each mutation has specific HRM profiles which could be used in rapid screening. The HRM method could correctly identify all genetic mutations in two children with β-ureidopropinoase deficiency. In addition, the HRM assay also recognized four unknown mutations. To conclude, the results support future studies of applying HRM analysis as a diagnostic approach for β-ureidopropinoase deficiency and a rapid screening method for UPB1 mutation carriers.

Automated production of CCR5-negative CD4+-T cells in a GMP-compatible, clinical scale for treatment of HIV-positive patients

Ex-vivo gene editing in T lymphocytes paves the way for novel concepts of immunotherapy. One of those strategies is directed at the protection of CD4⁺-T helper cells from HIV infection in HIV-positive individuals. To this end, we have developed and optimised a CCR5-targeting TALE nuclease, CCR5-Uco-hetTALEN, mediating high-efficiency knockout of C-C motif chemokine receptor 5 (CCR5), the HIV co-receptor essential during initial infection. Clinical translation of the knockout approach requires up-scaling of the manufacturing process to clinically relevant cell numbers in accordance with good manufacturing practice (GMP). Here we present a GMP-compatible mRNA electroporation protocol for the automated production of CCR5-edited CD4⁺-T cells in the closed CliniMACS Prodigy system. The automated process reliably produced high amounts of CCR5-edited CD4⁺-T cells (>1.5 × 10⁹ cells with >60% CCR5 editing) within 12 days. Of note, about 40% of total large-scale produced cells showed a biallelic CCR5 editing, and between 25 and 42% of produced cells had a central memory T-cell phenotype. In conclusion, transfection of primary T cells with CCR5-Uco-hetTALEN mRNA is readily scalable for GMP-compatible production and hence suitable for application in HIV gene therapy.

Optimisation of a TALE nuclease targeting the HIV co-receptor CCR5 for clinical application

Disruption of the C-C-Chemokine-receptor-5 (CCR5) gene induces resistance towards CCR5-tropic HIV. Here we optimised our previously described CCR5-Uco-TALEN and its delivery by mRNA electroporation. The novel variant, CCR5-Uco-hetTALEN features an obligatory heterodimeric Fok1-cleavage domain, which resulted in complete abrogation of off-target activity at previously found homodimeric as well as 7/8 in silico predicted, potential heterodimeric off-target sites, the only exception being highly homologous CCR2. Prevailing 18- and 10-bp deletions at the on-target site revealed microhomology-mediated end-joining as a major repair pathway. Notably, the CCR5^Δ55-60 protein resulting from the 18-bp deletion was almost completely retained in the cytosol. Simultaneous cutting at CCR5 and CCR2 induced rearrangements, mainly 15-kb deletions between the cut sites, in up to 2% of T cells underlining the necessity to restrict TALEN expression. We optimised in vitro mRNA production and showed that CCR5-on- and CCR2 off-target activities of CCR5-Uco-hetTALEN were limited to the first 72 and 24-48 h post-mRNA electroporation, respectively. Using single-cell HRMCA, we discovered high rates of TALEN-induced biallelic gene editing of CCR5, which translated in large numbers of CCR5-negative cells resistant to HIVenv-pseudotyped lentiviral vectors. We conclude that CCR5-Uco-hetTALEN transfected by mRNA electroporation facilitates specific, high-efficiency CCR5 gene-editing (30%-56%) and it is highly suited for clinical translation subject to further characterisation of off-target effects.

An interlocked DNA cascade system for universal probe-based melting curve analysis

Single-base mutations are the most common type of mutation in human diseases. Melting curve analysis is currently one of the most commonly used methods to detect single base mutations. However, the existing melting curve analysis cannot possess universality and robust detection performance simultaneously. Therefore, herein, we invented an interlocked DNA cascade system based universal melting curve analysis (ICU-MCA). The strategy is based on the probe dissolution curve method by designing a bridge strand to achieve an ideal distinction between mutant-type DNA and wild-type DNA. What is more, this method can complete multiplexed detection only by changing the bridge sequence, replacing the specific and expensive probe in a traditional probe based melting curve analysis. We performed 6-plex detection on 6 single-base point mutations in BRAC1/2 genes on synthetic single stranded DNA and verified the compatibility of ICU-MCA and PCR and detected BRCA1/c.2082C>T and BRCA2/c.7397T>C mutations in peripheral blood DNA of ovarian cancer patients. Overall, ICU-MCA is one of the best methods in the field of melting curve analysis for detecting single-base mutations.

Evaluation of high-resolution melting analysis for spa-typing of methicillin-resistant and -susceptible Staphylococcus aureus isolates

Molecular characterization of Staphylococcus aureus isolates from nosocomial and community-acquired infections using accurate, reproducible, and rapid typing methods is essential for the fast identification of prevalent and epidemic strains. Although sequence-based spa typing is highly effective, PCR-based techniques (such as high-resolution melting curve analysis, HRM) are simpler, less expensive, faster, and can be performed in a single and closed-tube assay format, thereby reducing the risk of contamination. A total of 51 methicillin-resistant S. aureus (MRSA) (n = 26) and methicillin-sensitive S. aureus (MSSA) (n = 25) isolates from Karaj (n = 10) and Yasuj (n = 41), Iran, were subjected to HRM. All selected isolates were identified by the standard spa-typing method. Among the 51 tested isolates, 11 genotype profiles were distinguished from 12 spa types. Strains t1077 and t1816 exhibited the highest and lowest melting temperatures (81.8°C and 79.4°C), with 46.7% and 39.8% G + C contents, respectively. Strains t706 and t1816, with almost identical G + C contents, had the same HRM genotypes, but their curves differed due to different G + C distributions. Four standard spa types (strains t030, t037, t701 and t5598) were differentiated correctly and their melting temperatures were 81.2°C, 81.4°C, 80.4°C and 80.1°C, respectively. We demonstrated that HRM profiling is a rapid method which enables the accurate screening of certain strains (especially the endemic ones), and may be used for bacterial surveillance. However, it cannot replace sequence-based spa typing, especially for newly emerging spa types, and therefore cannot be used as a standardized global method.

Insights on SNP types, detection methods and their utilization in Brassica species: Recent progress and future perspectives

The genus Brassica, family Brassicaceae (Cruciferae), comprises many important species of oil crops, vegetables and medicinal plants including B. rapa, B. oleracea, B. nigra, B. napus, B. juncea, B. carinata. Genomic researches in Brassica species is constrained by polyploidization, mainly due to its complicated genomic structure. However, rapid development of methods for detecting single nucleotide polymorphisms (SNP), such as next generation sequencing and SNP microarray, has accelerated release of reference Brassica species genomes as well as discovery of large numbers and genome-wide SNPs, thus intensifying forward genetics in this genus. In this review, we summarize biological characteristics, classification and various methods for detecting SNPs, focusing on high-throughput techniques. Moreover, we describe the pivotal roles of SNPs in genetic diversity, linkage map construction and QTL mapping, comparative genomics, linkage disequilibrium and genome-wide association studies. These insights are expected to deepen our understanding and guide further advancements in Brassica species research.

Use of a Plasmodium vivax genetic barcode for genomic surveillance and parasite tracking in Sri Lanka

Background

Sri Lanka was certified as a malaria-free nation in 2016; however, imported malaria cases continue to be reported. Evidence-based information on the genetic structure/diversity of the parasite populations is useful to understand the population history, assess the trends in transmission patterns, as well as to predict threatening phenotypes that may be introduced and spread in parasite populations disrupting elimination programmes. This study used a previously developed Plasmodium vivax single nucleotide polymorphism (SNP) barcode to evaluate the population dynamics of P. vivax parasite isolates from Sri Lanka and to assess the ability of the SNP barcode for tracking the parasites to its origin.

Methods

A total of 51 P. vivax samples collected during 2005–2011, mainly from three provinces of the country, were genotyped for 40 previously identified P. vivax SNPs using a high-resolution melting (HRM), single-nucleotide barcode method. Minor allele frequencies, linkage disequilibrium, pair-wise F_ST values, and complexity of infection (COI) were evaluated to determine the genetic diversity. Structure analysis was carried out using STRUCTURE software (Version 2.3.4) and SNP barcode was used to identify the genetic diversity of the local parasite populations collected from different years. Principal component analysis (PCA) was used to determine the clustering according to global geographic regions.

Results

The proportion of multi-clone infections was significantly higher in isolates collected during an infection outbreak in year 2007. The minor allele frequencies of the SNPs changed dramatically from year to year. Significant linkage was observed in sample sub-sets from years 2005 and 2007. The majority of the isolates from 2007 consisted of at least two genetically distinct parasite strains. The overall percentage of multi-clone infections for the entire parasite sample was 39.21%. Analysis using STRUCTURE software (Version 2.3.4) revealed the high genetic diversity of the sample sub-set from year 2007. In-silico analysis of these data with those available from other global geographical regions using PCA showed distinct clustering of parasite isolates according to geography, demonstrating the usefulness of the barcode in determining an isolate to be indigenous.

Conclusions

Plasmodium vivax parasite isolates collected during a disease outbreak in year 2007 were more genetically diverse compared to those collected from other years. In-silico analysis using the 40 SNP barcode is a useful tool to track the origin of an isolate of uncertain origin, especially to differentiate indigenous from imported cases. However, an extended barcode with more SNPs may be needed to distinguish highly clonal populations within the country.

Authentication of olive oil based on DNA analysis

Olive oil, which has been produced mainly in the Mediterranean area since the ancient times, has a high nutritional value linked to many health benefits. Extra virgin, which is the purest form of olive oil, has excellent quality and premium prices. Many cases of adulteration and fraud necessitate the development of reliable and accurate methods for olive oil authentication. DNA-based methods analyze the residual DNA extracted from olive oil and use molecular markers for genetic identification of different species, subspecies or cultivars because these markers act as signs which reflect distinct genetic profiles. This study reviews the process by which DNA from olive oil is extracted and analyzed by the most recently used markers in the authentication of olive oil, such as Simple Sequence Repeats (SSR) or microsatellites and the single nucleotide polymorphisms (SNPs). Methods of analysis such as qPCR and digital PCR are also discussed with a special emphasis placed on the method of High-Resolution Melting (HRM), a post-polymerase chain reaction method, which enables rapid, high performing identification of genetic variants in the DNA regions of interest without sequencing, and may differentiate very similar cultivars which differ in only one nucleotide in a specific locus.

Expanded Instrument Comparison of Amplicon DNA Melting Analysis for Mutation Scanning and Genotyping

Background: Additional instruments have become available since instruments for DNA melting analysis of PCR products for genotyping and mutation scanning were compared. We assessed the performance of these new instruments for genotyping and scanning for mutations.

Methods: A 110-bp fragment of the β-globin gene including the sickle cell anemia locus (HBB c. 20A&gt;T) was amplified by PCR in the presence of LCGreen Plus or SYBR Green I. Amplicons of 4 different genotypes [wild-type, homozygous, and heterozygous HBB c. 20A&gt;T and double-heterozygote HBB c. (9C&gt;T; 20A&gt;T)] were melted on 7 different instruments [Applied Biosystems 7300, Corbett Life Sciences Rotor-Gene 6500HRM, Eppendorf Mastercycler RealPlex4S, Idaho Technology LightScanner (384 well), Roche LightCycler 480 (96 and 384 well) and Stratagene Mx3005p] at a rate of 0.61 °C/s or when this was not possible, at 0.50 °C steps. We evaluated the ability of each instrument to genotype by melting temperature (Tm) and to scan for heterozygotes by curve shape.

Results: The ability of most instruments to accurately genotype single-base changes by amplicon melting was limited by spatial temperature variation across the plate (SD of Tm = 0.020 to 0.264 °C). Other variables such as data density, signal-to-noise ratio, and melting rate also affected heterozygote scanning.

Conclusions: Different instruments vary widely in their ability to genotype homozygous variants and scan for heterozygotes by whole amplicon melting analysis. Instruments specifically designed for high-resolution melting, however, displayed the least variation, suggesting better genotyping accuracy and scanning sensitivity and specificity.

Removal of artifact bias from qPCR results using DNA melting curve analysis

Quantitative PCR (qPCR) allows the precise measurement of DNA concentrations and is generally considered to be straightforward and trouble free. However, analyses using validated Sybr Green I-based assays regularly amplify both the correct product and an artifact. Amplification of more than 1 product can be recognized when melting curve analysis is performed after the qPCR. Currently, such reactions need to be excluded from further analysis because the quantification result is considered meaningless. However, when the fraction of the fluorescence associated with the correct product can be determined, the quantitative result of the qPCR analysis can be corrected. The main assumptions of this correction model are: 1) the melting peak of the correct product can be identified, 2) the PCR efficiencies of all amplified products are similar, 3) the relative size of the melting peaks reflects the relative concentrations of the products, and 4) the relative concentrations do not change as the reaction reaches plateau. These assumptions were validated in a series of model experiments. The results show that the quantitative results can be corrected. Implementation of a correction for the presence of artifact amplification in the analysis of qPCR data leads to more reliable quantitative results in qPCR experiments.-Ruijter, J. M., Ruiz-Villalba, A., van den Hoff, A. J. J., Gunst, Q. D., Wittwer, C. T., van den Hoff, M. J. B. Removal of artifact bias from qPCR results using DNA melting curve analysis.

An HRM Assay to Differentiate Sheeppox Virus Vaccine Strains from Sheeppox Virus Field Isolates and other Capripoxvirus Species

Sheep poxvirus (SPPV), goat poxvirus (GTPV) and lumpy skin disease virus (LSDV) affect small ruminants and cattle causing sheeppox (SPP), goatpox (GTP) and lumpy skin disease (LSD) respectively. In endemic areas, vaccination with live attenuated vaccines derived from SPPV, GTPV or LSDV provides protection from SPP and GTP. As live poxviruses may cause adverse reactions in vaccinated animals, it is imperative to develop new diagnostic tools for the differentiation of SPPV field strains from attenuated vaccine strains. Within the capripoxvirus (CaPV) homolog of the variola virus B22R gene, we identified a unique region in SPPV vaccines with two deletions of 21 and 27 nucleotides and developed a High-Resolution Melting (HRM)-based assay. The HRM assay produces four distinct melting peaks, enabling the differentiation between SPPV vaccines, SPPV field isolates, GTPV and LSDV. This HRM assay is sensitive, specific, and provides a cost-effective means for the detection and classification of CaPVs and the differentiation of SPPV vaccines from SPPV field isolates.

Single-color multiplexing by the integration of high-resolution melting pattern recognition with loop-mediated isothermal amplification

We develop a single-color multiplexing strategy by the integration of high-resolution melting pattern recognition with loop-mediated isothermal amplification (LAMP). This strategy can identify multiple amplicons with a small DNA melting temperature (Tm) difference (∼0.2 °C) without the involvement of either multicolor labels or parallelized multiplexing, and it can sensitively detect LAMP amplicons with the initial DNA concentrations ranging from 10 to 108 copies.

Cost-effective and robust genotyping using double-mismatch allele-specific quantitative PCR

For a wide range of diseases, SNPs in the genome are the underlying mechanism of dysfunction. Therefore, targeted detection of these variations is of high importance for early diagnosis and (familial) screenings. While allele-specific PCR has been around for many years, its adoption for SNP genotyping or somatic mutation detection has been hampered by its low discriminating power and high costs. To tackle this, we developed a cost-effective qPCR based method, able to detect SNPs in a robust and specific manner. This study describes how to combine the basic principles of allele-specific PCR (the combination of a wild type and variant primer) with the straightforward readout of DNA-binding dye based qPCR technology. To enhance the robustness and discriminating power, an artificial mismatch in the allele-specific primer was introduced. The resulting method, called double-mismatch allele-specific qPCR (DMAS-qPCR), was successfully validated using 12 SNPs and 15 clinically relevant somatic mutations on 48 cancer cell lines. It is easy to use, does not require labeled probes and is characterized by high analytical sensitivity and specificity. DMAS-qPCR comes with a complimentary online assay design tool, available for the whole scientific community, enabling researchers to design custom assays and implement those as a diagnostic test.

Aberrant DNA methylation of M1-macrophage genes in coronary artery disease

M1 and M2 macrophage balance in atherosclerosis has attracted much interest. Though, it remains unknown how macrophage heterogeneity is regulated. Moreover, the regulation of macrophage polarization and activation also involve DNA methylation. However, it remains ambiguous which genes are under direct regulation by DNA methylation. Our aim was to evaluate the gene-specific promoter DNA methylation status of M1/M2 polarization markers in PBMCs of CAD patients. A case-control study was performed with 25 CAD patients and 25 controls to study the promoter DNA methylation status of STAT1, STAT6, MHC2, IL12b, iNOS, JAK1, JAK2 and SOCS5 using MS-HRM analysis. Our data indicates that there was a clear-cut difference in the pattern of gene-specific promoter DNA methylation of CAD patients in comparison to controls. A significant difference was observed between the percentage methylation of STAT1, IL12b, MHC2, iNOS, JAK1 and JAK2 in CAD patients and control subjects. In conclusion, our data show that MS-HRM assay is a rapid and inexpensive method for qualitatively identifying aberrant gene-specific promoter DNA methylation changes in CAD. Furthermore, we propose that gene-specific promoter DNA methylation based on monocyte/macrophage might aid as diagnostic marker for clinical application or DNA methylation-related drug interventions may offer novel possibilities for atherosclerotic disease management.

Turkey humoral and cell-mediated immune responses to a Newcastle viscerotropic vaccine and its association with major histocompatibility complex

Immune responses to vaccines are mainly influenced by the nature of vaccines and host variation in response to vaccination. In this study we aimed to investigate turkey humoral and cell-mediated immune responses to a Newcastle viscerotropic vaccine and its association with major histocompatibility complex (MHC). Turkeys were vaccinated with Villegas–Glisson/University of Georgia (VG/GA) attenuated vaccine against Newcastle disease. The stimulation index of lymphocyte proliferation and antigen-specific local secretory IgA responses in bile, duodenum, ileum, as well as serum IgY and IgA responses were analysed by enzyme-linked immunosorbent assay. The turkey MHC class II B locus was selected as candidate gene for detection of associations with cellular and humoral immune responses. Significant differences were observed between both cellular and humoral responses of vaccinated and unvaccinated groups. A significant positive correlation was also found between ND specific IgY and ND specific IgA titres in serum, intestine (duodenum and ileum) and trachea. Moreover, the correlation between specific IgA titres in ileum and specific bile, duodenum and trachea was positively significant. High resolution melting analysis (HRM) was used to genotype MHC class II B exon 2. Eight melting profiles (A-G) were identified, among which, profile G showed a significant association with cellular response. The profile B revealed significant association with total IgA titres in serum and ileum. These findings help our understanding of the association of turkey MHC types with immune responses. Further correlation analysis between serum and mucosal antibody titres demonstrated that the levels of IgY and IgA in serum can give an impression about the levels of secretory IgA and situation of mucosal immunity. Based on the significant effects, ND specific IgY in serum appears to be a promising indirect marker for specific IgA in serum and trachea.

Expression of activating transcription factor 5 (ATF5) is increased in astrocytomas of different WHO grades and correlates with survival of glioblastoma patients

Background

ATF5 suppresses differentiation of neuroprogenitor cells and is overexpressed in glioblastoma (GBM). A reduction of its expression leads to apoptotic GBM cell death. Data on ATF5 expression in astrocytoma WHO grade II (low-grade astrocytoma [LGA]) are scarce and lacking on recurrent GBM.

Patients and methods

ATF5 mRNA was extracted from frozen samples of patients’ GBM (n=79), LGA (n=40), and normal brain (NB, n=10), quantified by duplex qPCR and correlated with retrospectively collected clinical data. ATF5 protein expression was evaluated by measuring staining intensity on immunohistochemistry.

Results

ATF5 mRNA was overexpressed in LGA (sevenfold, P<0.001) and GBM (tenfold, P<0.001) compared to NB, which was confirmed on protein level. Although ATF5 mRNA expression in GBM showed a considerable fluctuation range, groups of varying biological behavior, that is, local/multifocal growth or primary tumor/relapse and the tumor localization at diagnosis, were not significantly different. ATF5 mRNA correlated with the patients’ age (r=0.339, P=0.028) and inversely with Ki67-staining (r=−0.421, P=0.007). GBM patients were allocated to a low and a high ATF5 expression group by the median ATF5 overexpression compared to NB. Kaplan–Meier analysis and Cox regression indicated that ATF5 mRNA expression significantly correlated with short-term survival (t,12 months, median survival 18 vs 13 months, P=0.022, HR 2.827) and progression-free survival (PFS) (12 vs 6 months, P=0.024). This advantage vanished after 24 months (P=0.084).

Conclusion

ATF5 mRNA expression could be identified as an additional, though not independent factor correlating with overall survival and PFS. Since its inhibition might lead to the selective death of glioma cells, it might serve as a potential ubiquitous therapeutic target in astrocytic tumors.

Development and validation of a rapid method for genotyping three P-selectin gene polymorphisms based on high resolution melting analysis

BACKGROUND

High resolution melting (HRM) analysis is one of the newer, reliable, and sensitive genotyping techniques, which offers considerable time and cost savings. P-selectin is an adhesion molecule that has a role in the initial phases of leukocyte adhesion to stimulated platelets and endothelial cells in inflammation. Multiple polymorphisms in P-selectin gene (SELP) that affect the protein sequence have been described. The aim of this study was to design, optimize, and validate a simple and rapid in-house HRM-based method for genotyping the NM_003005.3:c.992G>A (c.992G>A), NM_003005.3:c.1918G>T (c.1918G>T), and NM_003005.3:c.2266A>C (c.2266A>C) SELP polymorphisms.

METHODS

Initial genotyping of three SELP polymorphisms was performed by applying polymerase chain reaction (PCR) with sequence-specific primers (SSP), which was used as a reference method for determination of analytical sensitivity. PCR-HRM was performed with primers for c.2266A>C reported in the literature. Primers for the remaining two polymorphisms were designed using Primer-BLAST. Precision testing was performed using three samples with different genotypes. For accuracy, analytical sensitivity and specificity testing, 20 wild type, 10 heterozygous, and 10 homozygous samples were chosen per polymorphism. Results were expressed as percentage of concordance with the acceptability criterion ≥95%.

RESULTS

Agreement of results was 100% for all validation parameters except for analytical sensitivity for c.1918G>T and c.2266A>C, with agreement of 90%. Repeated analysis using both methods revealed an error in initial genotyping and correct genotyping by PCR-HRM, which was confirmed by Sanger sequencing.

CONCLUSION

The validation confirmed PCR-HRM as a precise, accurate, and specific method for genotyping the c.992G>A, c.1918G>T, and c.2266A>C SELP polymorphisms.

High Resolution Melting Temperature Analysis to IdentifyCRISPR/Cas9 Mutants from Arabidopsis

CRISPR/Cas9 made targeted mutagenesis and genome editing possible for many plant species. One of the ways that the endonuclease is used for plant genetics is the creation of loss-of-function mutants, which typically result from erroneous DNA repair through non-homologous end joining (NHEJ) pathway. The majority of erroneous repair events results in single-bp insertion or deletion. While single-bp insertions or deletions (indels) effectively destroy the function of protein-coding genes through frameshift, detection is difficult due to the small size shift. High-resolution melting temperature analysis allows quick detection, and it does not require any additional pipetting steps after the PCR amplification of the region of interest. In this protocol, we will describe the steps required for the analysis of potential homozygous mutants.

Amino acid permease 3 (aap3) coding sequence as a target for Leishmania identification and diagnosis of leishmaniases using high resolution melting analysis

Background

The leishmaniases comprise a spectrum of clinical manifestations caused by different species of Leishmania. Identification of species is important for diagnosis, treatment and follow-up management. However, there is no gold standard for species identification. High resolution melting analysis (HRM) offers a possibility to differentiate Leishmania species without the need for processing of the PCR-product. The amino acid permease 3 (aap3) gene is an exclusive target for trypanosomatids and is conserved among Leishmania spp., thus it can be a valuable target for an HRM assay for diagnosis of the leishmaniases.

Results

The HRM dissociation profiles of three amplicons targeting the aap3-coding region allowed the discrimination of L. (Leishmania) donovani, L. (L.) infantum, L. (L.) major, L. (L.) tropica, L. (L.) mexicana, L. (L.) amazonensis, L. (Viannia) braziliensis, L. (V.) guyanensis, L. (V.) lainsoni, L. (V.) naiffi and L. (V.) shawi using DNA from promastigote cultures. The protocol was validated with DNA samples from clinical infection in humans and a cat, naturally infected sand flies, and experimentally infected mice.

Conclusions

HRM analysis using the aap3 coding sequence as target is a relatively cheap, fast and robust strategy to detect and discriminate Leishmania species from all the endemic regions worldwide. The target and method proved to be useful in clinical, field and experimental samples, thus it could be used as a tool in diagnosis as well as ecological and epidemiological studies.

Electronic supplementary material

The online version of this article (10.1186/s13071-018-2989-z) contains supplementary material, which is available to authorized users.

Comparison of three molecular methods for species identification of the family Cichlidae in Kwan Phayao, Thailand

The species diversity of cichlids was investigated in Kwan Phayao from August 2016 to May 2017. Four cichlid species were found, including Oreochromis niloticus, Oreochromis mossambicus, Coptodon rendalli and Coptodon zillii. Due to similar characterizations, it is very difficult to identify each species. Three molecular methods were used to distinguish these four species. DNA barcodes or partial cytochrome c oxidase I (COI) gene sequences were amplified by PCR and sequenced. In Oreochromis sp. and Coptodon sp., 707- and 704-bp fragments were amplified, respectively. Polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) analysis showed clear differences between the four cichlid species after digestion with three restriction enzymes, ScaI, HindIII and PdiI. ScaI and HindIII separated Oreochromis sp. from Coptodon sp. due to different fragment sizes. PdiI distinguished each cichlid species in the same genus. Finally, high resolution melting (HRM) analysis showed the sensitivity of the primers for discriminating these species with small amplicons and melting curves. From the comparison, HRM analysis was the most efficient method because the primer was shown to be sensitive for discriminating the four cichlids. In addition, it was inexpensive and required a short time to detect large samples. However, direct sequencing or DNA barcodes were still necessary in the case of the COI sequences of organisms of interest, which have not been reported in any databases. These four cichlids are alien species in Thailand; thus, species identification is very important for fishery management.

A High-Resolution Digital DNA Melting Platform for Robust Sequence Profiling and Enhanced Genotype Discrimination

DNA melting analysis provides a rapid method for genotyping a target amplicon directly after PCR amplification. To transform melt genotyping into a broad-based profiling approach for heterogeneous samples, we previously proposed the integration of universal PCR and melt analysis with digital PCR. Here, we advanced this concept by developing a high-resolution digital melt platform with precise thermal control to accomplish reliable, high-throughput heat ramping of microfluidic chip digital PCR reactions. Using synthetic DNA oligos with defined melting temperatures, we characterized sources of melting variability and minimized run-to-run variations. Within-run comparisons throughout a 20,000-reaction chip revealed that high-melting-temperature sequences were significantly less prone to melt variation. Further optimization using bacterial 16S amplicons revealed a strong dependence of the number of melting transitions on the heating rate during curve generation. These studies show that reliable high-resolution melt curve genotyping can be achieved in digital, picoliter-scale reactions and demonstrate that rate-dependent melt signatures may be useful for enhancing automated melt genotyping.

CtGEM typing: Discrimination of Chlamydia trachomatis ocular and urogenital strains and major evolutionary lineages by high resolution melting analysis of two amplified DNA fragments

Chlamydia trachomatis infects the urogenital tract (UGT) and eyes. Anatomical tropism is correlated with variation in the major outer membrane protein encoded by ompA. Strains possessing the ocular ompA variants A, B, Ba and C are typically found within the phylogenetically coherent “classical ocular lineage”. However, variants B, Ba and C have also been found within three distinct strains in Australia, all associated with ocular disease in children and outside the classical ocular lineage. CtGEM genotyping is a method for detecting and discriminating ocular strains and also the major phylogenetic lineages. The rationale was facilitation of surveillance to inform responses to C. trachomatis detection in UGT specimens from young children. CtGEM typing is based on high resolution melting analysis (HRMA) of two PCR amplified fragments with high combinatorial resolving power, as defined by computerised comparison of 65 whole genomes. One fragment is from the hypothetical gene defined by Jali-1891 in the C. trachomatis B_Jali20 genome, while the other is from ompA. Twenty combinatorial CtGEM types have been shown to exist, and these encompass unique genotypes for all known ocular strains, and also delineate the TI and T2 major phylogenetic lineages, identify LGV strains and provide additional resolution beyond this. CtGEM typing and Sanger sequencing were compared with 42 C. trachomatis positive clinical specimens, and there were no disjunctions. CtGEM typing is a highly efficient method designed and tested using large scale comparative genomics. It divides C. trachomatis into clinically and biologically meaningful groups, and may have broad application in surveillance.

Emerging Technologies for Molecular Diagnosis of Sepsis

Rapid and accurate profiling of infection-causing pathogens remains a significant challenge in modern health care. Despite advances in molecular diagnostic techniques, blood culture analysis remains the gold standard for diagnosing sepsis. However, this method is too slow and cumbersome to significantly influence the initial management of patients. The swift initiation of precise and targeted antibiotic therapies depends on the ability of a sepsis diagnostic test to capture clinically relevant organisms along with antimicrobial resistance within 1 to 3 h. The administration of appropriate, narrow-spectrum antibiotics demands that such a test be extremely sensitive with a high negative predictive value. In addition, it should utilize small sample volumes and detect polymicrobial infections and contaminants. All of this must be accomplished with a platform that is easily integrated into the clinical workflow. In this review, we outline the limitations of routine blood culture testing and discuss how emerging sepsis technologies are converging on the characteristics of the ideal sepsis diagnostic test. We include seven molecular technologies that have been validated on clinical blood specimens or mock samples using human blood. In addition, we discuss advances in machine learning technologies that use electronic medical record data to provide contextual evaluation support for clinical decision-making.

Identification of Postharvest Senescence Regulators Through Map-Based Cloning Using Detached Arabidopsis Inflorescences as a Model Tissue

Postharvest deterioration of fruits and vegetables can be accelerated by biological, environmental, and physiological stresses. Fully understanding tissue response to harvest will provide new opportunities for limiting postharvest losses during handling and storage. The model plant Arabidopsis thaliana (Arabidopsis) has many attributes that make it excellent for studying the underlying control of postharvest responses. It is also one of the best resourced plants with numerous web-based bioinformatic programs and large numbers of mutant collections. Here we introduce a novel assay system called AIDA (the Arabidopsis Inflorescence Degreening Assay) that we developed for understanding postharvest response of immature tissues. We also demonstrate how the high-throughput screening capability of AIDA can be used with mapping technologies (high-resolution melting [HRM] and needle in the k-stack [NIKS]) to identify regulators of postharvest senescence in ethyl methanesulfonate (EMS) mutagenized plant populations. Whether it is best to use HRM or NIKS or both technologies will depend on your laboratory facilities and computing capabilities.

DNA methylation assay using droplet-based DNA melting curve analysis

DNA methylation is an epigenetic regulation of gene expression, which has drawn great attention in biomedical research due to its association with various diseases. A robust, inexpensive platform to detect and quantify the methylation status in a specific genomic region is necessary. In this study, an on-chip analytical technique of cytosine methylation with droplets in a microchannel is proposed. Genomic DNA samples are encapsulated into a series of droplets and transported through a detection region, where a stable temperature gradient is created. As the temperature is elevated from 60 °C to 85 °C, the DNA samples denature and the associated fluorescence signals decay, with the relationship being acquired as the melting curve. The droplets serve as discrete reactors for conducting DNA melting curve analysis in the liquid phase, thereby eliminating the need for immobilization of reagents. Due to a high heating rate and greater enhanced thermal stability, this microchip allows larger melting temperature differences for the samples at different percentages of methylated DNA. It has an enhanced discrimination ability and lower volume consumption, compared to the commercial qPCR machine. This chip enables quantification of the methylation levels of the pluripotent stem cell factor Oct-4 in its distal enhancer (DE) region, with a designed probe after bisulfite treatment and asymmetric PCR.

Genotyping by Sequencing Highlights a Polygenic Resistance to Ralstonia pseudosolanacearum in Eggplant (Solanum melongena L.)

Eggplant cultivation is limited by numerous diseases, including the devastating bacterial wilt (BW) caused by the Ralstonia solanacearum species complex (RSSC). Within the RSSC, Ralstonia pseudosolanacearum (including phylotypes I and III) causes severe damage to all solanaceous crops, including eggplant. Therefore, the creation of cultivars resistant to R. pseudosolanacearum strains is a major goal for breeders. An intraspecific eggplant population, segregating for resistance, was created from the cross between the susceptible MM738 and the resistant EG203 lines. The population of 123 doubled haploid lines was challenged with two strains belonging to phylotypes I (PSS4) and III (R3598), which both bypass the published EBWR9 BW-resistance quantitative trait locus (QTL). Ten and three QTLs of resistance to PSS4 and to R3598, respectively, were detected and mapped. All were strongly influenced by environmental conditions. The most stable QTLs were found on chromosomes 3 and 6. Given their estimated physical position, these newly detected QTLs are putatively syntenic with BW-resistance QTLs in tomato. In particular, the QTLs' position on chromosome 6 overlaps with that of the major broad-spectrum tomato resistance QTL Bwr-6. The present study is a first step towards understanding the complex polygenic system, which underlies the high level of BW resistance of the EG203 line.

Saturated genic SNP mapping identified functional candidates and selection tools for the Pinus monticola Cr2 locus controlling resistance to white pine blister rust

Molecular breeding incorporates efficient tools to increase rust resistance in five-needle pines. Susceptibility of native five-needle pines to white pine blister rust (WPBR), caused by the non-native invasive fungus Cronartium ribicola (J.C. Fisch.), has significantly reduced wild populations of these conifers in North America. Major resistance (R) genes against specific avirulent pathotypes have been found in several five-needle pine species. In this study, we screened genic SNP markers by comparative transcriptome and genetic association analyses and constructed saturated linkage maps for the western white pine (Pinus monticola) R locus (Cr2). Phenotypic segregation was measured by a hypersensitive reaction (HR)-like response on the needles and disease symptoms of cankered stems post inoculation by the C. ribicola avcr2 race. SNP genotypes were determined by HRM- and TaqMan-based SNP genotyping. Saturated maps of the Cr2-linkage group (LG) were constructed in three seed families using a total of 34 SNP markers within 21 unique genes. Cr2 was consistently flanked by contig_2142 (encoding a ruvb-like protein) and contig_3772 (encoding a delta-fatty acid desaturase) across the three seed families. Cr2 was anchored to the Pinus consensus LG-1, which differs from LGs where other R loci of Pinus species were mapped. GO annotation identified a set of NBS-LRR and other resistance-related genes as R candidates in the Cr2 region. Association of one nonsynonymous SNP locus of an NBS-LRR gene with Cr2-mediated phenotypes provides a valuable tool for marker-assisted selection (MAS), which will shorten the breeding cycle of resistance screening and aid in the restoration of WPBR-disturbed forest ecosystems.

Should DNA sequence be incorporated with other taxonomical data for routine identifying of plant species?

Background

A variety of plants in Acanthaceae have long been used in traditional Thai ailment and commercialised with significant economic value. Nowadays medicinal plants are sold in processed forms and thus morphological authentication is almost impossible. Full identification requires comparison of the specimen with some authoritative sources, such as a full and accurate description and verification of the species deposited in herbarium. Intake of wrong herbals can cause adverse effects. Identification of both raw materials and end products is therefore needed.

Methods

Here, the potential of a DNA-based identification method, called Bar-HRM (DNA barcoding coupled with High Resolution Melting analysis), in raw material species identification is investigated. DNA barcode sequences from five regions (matK, rbcL, trnH-psbA spacer region, trnL and ITS2) of Acanthaceae species were retrieved for in silico analysis. Then the specific primer pairs were used in HRM assay to generate unique melting profiles for each plants species.

Results

The method allows identification of samples lacking necessary morphological parts. In silico analyses of all five selected regions suggested that ITS2 is the most suitable marker for Bar-HRM in this study. The HRM analysis on dried samples of 16 Acanthaceae medicinal species was then performed using primer pair derived from ITS2 region. 100% discrimination of the tested samples at both genus and species level was observed. However, two samples documented as Clinacanthus nutans and Clinacanthus siamensis were recognised as the same species from the HRM analysis. Further investigation reveals that C. siamensis is now accepted as C. nutans.

Conclusions

The results here proved that Bar-HRM is a promising technique in species identification of the studied medicinal plants in Acanthaceae. In addition, molecular biological data is currently used in plant taxonomy and increasingly popular in recent years. Here, DNA barcode sequence data should be incorporated with morphological characters in the species identification.

High Resolution Melting Analysis is Very Useful to Identify BRCA1 c.4964_4982del19 (rs80359876) Founder Calabrian Pathogenic Variant on Peripheral Blood and Buccal Swab DNA

INTRODUCTION

Detection of pathogenic variants in hereditary breast and ovarian cancer-related breast cancer type 1 and type 2 susceptibility proteins (BRCA1/2) genes is an effective strategy in cancer prevention and treatment. Some ethnic and geographical regions show different BRCA1/2 mutation spectrum and prevalence. In Italy, elucidation of founder effect in BRCA1/2 genes can have an impact on the management of hereditary cancer families on a healthcare system level, making genetic testing more affordable and cost effective in certain regions.

METHODS

The purpose of this paper is to develop a rapid, low-cost, high-throughput single-tube technology for genotyping the Italian founder mutation c.4964_4982del19 (rs80359876) in the BRCA1 gene, starting from peripheral blood and/or buccal swab DNA.

RESULTS

Heterozygote samples for c.4964_4982del19 variant were easily and unambiguously identified by the altered shape of the melting curves and were clearly distinguished by a change in melting temperature that differed by approximately 5 °C. The same results were obtained both with DNA from peripheral blood than buccal swab.

CONCLUSIONS

We provide evidence about application of high-resolution melting analysis (HRMA) in unambiguously genotyping of the founder BRCA1 c.4964_4982del19 variant (rs80359876) in individuals from the Calabria region of Italy. In fact, HRMA was confirmed to be particularly suitable for the identification of BRCA1 c.4964_4982del19 variant, making this approach useful in clinical molecular diagnostics.

HRM and SNaPshot as alternative forensic SNP genotyping methods

Single nucleotide polymorphisms (SNPs) have been widely used in forensics for prediction of identity, biogeographical ancestry (BGA) and externally visible characteristics (EVCs). Single base extension (SBE) assays, most notably SNaPshot® (Thermo Fisher Scientific), are commonly used for forensic SNP genotyping as they can be employed on standard instrumentation in forensic laboratories (e.g. capillary electrophoresis). High resolution melt (HRM) analysis is an alternative method and is a simple, fast, single tube assay for low throughput SNP typing. This study compares HRM and SNaPshot®. HRM produced reproducible and concordant genotypes at 500 pg, however, difficulties were encountered when genotyping SNPs with high GC content in flanking regions and differentiating variants of symmetrical SNPs. SNaPshot® was reproducible at 100 pg and is less dependent on SNP choice. HRM has a shorter processing time in comparison to SNaPshot®, avoids post PCR contamination risk and has potential as a screening tool for many forensic applications.