Insertions Or Deletions Research Articles

A comprehensive guide to bioinformatics tools and databases

The interest in the functional aspects of the genome has increased eventually with the expansion of genomic databases. In this review, various genetic alterations within the genome, such as Single Nucleotide Polymorphisms (SNPs), disease-associated mutations, neutral polymorphisms, and small insertions or deletions (INDELs), have been identified and characterized. These polymorphisms, particularly SNPs, have become widely employed in genetic analyses, serving as valuable molecular markers. They are applied across diverse genetic studies, including the reconstruction of haplotypes. In addition to experimental methods for investigating specific genetic variants, there has been a significant surge in bioinformatics research over the past decade, aimed at the molecular consequences of these genetic alterations. Haplotypes, which represent various alleles of a gene, can be reconstructed not only for entire chromosomes but also for specific genes, utilizing the information derived from SNPs. The computational approach to SNP and haplotype discovery has gained prominence due to the continuous expansion of sequence data within public databases. This growth enables more precise identification of SNPs. This article aims to introduce easily accessible and practical online tools for researchers. In summary, SNP and haplotype identification tools are indispensable in bioinformatics for studying genetic variation, population genetics, disease associations, and personalized medicine. They provide valuable insights into the genetic underpinnings of various traits and diseases, helping advance our understanding of genetics and its applications in healthcare.

Molecular profiling of Chinese systemic anaplastic large cell lymphoma patients: novel evidence of genetic heterogeneity.

BackgroundAnaplastic large cell lymphoma (ALCL) is a rare non-Hodgkin lymphoma. A comprehensive understanding of the genetic and clinical heterogeneity of ALCL may help to improve the clinical management of patients with ALCL. However, due to the rarity of the disease, the genetic heterogeneity of ALCL has not been well elucidated. This study aimed to comprehensively elucidate the mutational landscape of tumor tissue samples from patients with systemic ALCL.MethodsThirty-six patients with systemic ALCL were enrolled in this retrospective study. Immunohistochemistry (IHC) was performed on tumor tissues at baseline to identify anaplastic lymphoma kinase (ALK) fusions. Capture-based targeted next-generation sequencing (NGS) with a panel spanning 112 lymphoma-related genes, including ALK rearrangements, was also performed on tumor tissue samples.ResultsA total of 102 mutations were identified in the entire cohort. Among the 36 patients included in this analysis, 14 (38.8%) were ALK positive, as determined by IHC, while NGS showed 12 patients (33.3%) to harbor ALK rearrangements. Younger patients were more likely to have ALK-positive ALCL (P=0.011). Patients with wild-type (WT) ALK were more likely to have single-nucleotide variants (SNVs) and insertions or deletions (INDELs) than patients with ALK rearrangements (P=0.027). Among the 22 patients with WT ALK, the most commonly mutated genes were TP53 (n=6, 27.3%), followed by NOTCH1 (n=5, 22.7%), KMT2D (n=3, 13.6%), KRAS (n=3, 13.6%), TET2 (n=3, 13.6%), and JAK1 (n=2, 9.1%). Mutations in PRDM1, a commonly mutated gene in ALK-negative patients, were not detected in our ALK-negative cohort. Start-loss of beta-2-microglobulin (B2M) was detected in another patient; this patient had a favorable prognosis, with an overall survival exceeding 19 months.ConclusionsOur study revealed the unique genomic profiles of Chinese ALCL patients and represents an incremental step in deepening the understanding of the genetic heterogeneity of ALCL patients.

Genomic profiling of pulmonary lymphoepithelioma-like carcinoma (PLELC).

1572 Background: PLELC, a rare and distinct type of primary lung cancer, is characterized by Epstein-Barr virus (EBV) infection. Histologically, it resembles undifferentiated nasopharyngeal carcinomas (NPC). Only a few hundred cases have been reported since its discovery. Due to the extreme rareness, its genomic landscape remains elusive. Methods: Tissue samples of 27 PLELC patients (13 males and 14 females) with various stages (Ib to IV) were subjected to targeted sequencing using a panel consisting of 520 cancer-related genes, spanning 1.6Mb of human genome. Results: Collectively, we identified 184 somatic mutations spanning 109 genes, including 107 SNVs, 12 insertions or deletions (INDELs) and 65 copy-number amplifications (CNAs). Approximately, 50% of patients had CNAs. One patient had no mutation detected from this panel. Except for 2 patients, 1 with HER2 amplification and another with KRAS mutation, no other classic NSCLC driver genes were detected. The most frequently mutated genes were CCND1, TP53, DAXX and NF kBIA, occurring in 30%, 26%, 22% and 22% of patients, respectively. Interestingly, 78% (21/27) patients had mutations in epigenetic regulators. Of the 184 mutations identified, 51 occurred in epigenetics-related genes. Pathway analysis also revealed an enrichment of genes participating in chromatin remodeling and organization. Next, we compared the genomic profile of PLELC with lung adenocarcinoma and EBV positive NPC. The frequency of TP53 mutations was significantly higher in lung adenocarcinoma (68% vs 26%, p = 0.021). Comparing to NPC, PLELC had significantly more mutations in epigenetic regulators. TMB analysis revealed a median TMB of 1.6/Mb, significantly lowered than lung adenocarcinomas (p < 0.01). We also assessed PD-L1expression and revealed that 67% had an overexpression of PD-L1. Interestingly, TP53-mutant patients were more likely to associated low PD-L1 expression (p < 0.01). Conclusions: In this study, we elucidated a distinct genomic landscape associated with PLELC with no classic NSCLC driver mutation but an enrichment of mutations in epigenetic regulators. The observation of high expression of PD-L1 and lack of canonical druggable driver mutation raises the potential of immunocheckpoint blockade therapy for PLELC.

Abstract P4-04-05: Spatial heterogeneity revealed by genomic profiles comparing 60 matched primary breast tumors and metastatic lymph nodes

Abstract Background: Genomic profiling in primary breast tumors has been extensively performed and reveals the heterogenous complexity in mutational landscape of the disease. However, little is known about differential mutation spectrums in synchronous breast tumors and matched metastasis in axillary lymph nodes. To characterize the spatial heterogeneity and identify potential biological mechanisms involved in the lymph node metastasis, we determined the genomic mutational profiles in synchronous primary lesion (PL) and metastatic lymph nodes (MLN) by using ultra-deep targeted sequencing. Methods: Targeted deep sequencing was performed using a panel including 520 cancer-related genes and spanning 1.6MB of human genome. The mutational profiles were compared between the matched PL and MLN samples from 60 of treatment-naïve patients with invasive breast cancer and axillary lymph node metastasis. KEGG enrichment analysis was further performed between specific and shared mutations in either PL or MLN samples. The relationship between spatial heterogeneity and clinical characteristics was also explored. Results: The cohort had a median age of 45 (ranging from 28-67), with a majority (86.7%) of them diagnosed with infiltrating ductal carcinoma. In this 60-paired cohort, 961 genomic aberrations were identified in 242 genes, including 405 single nucleotide variants (SNVs), 66 insertions or deletions (INDELs), 482 copy-number amplifications (CNAs), and 8 translocations. Although 584 (60.8%) events were shared in PL and MLN samples, 226 (23.5%) mutations spanning 51 genes and 151 (15.7%) mutations involving 46 genes were specific PL and MLN samples, respectively. In addition, 7 of patients (11.7%), all of whom are hormonal receptor (HR) positive, harbored completely similar mutation spectrum between PL and MLN. Twenty-one patients (35%) had PL specific mutations, but had no MLN specific mutations. In contrast, 6 patients (10%) only had MLN specific mutations and the remaining 26 patients (43.3%) had both PL and MLN specific mutations. Interestingly, the Ki67-based proliferation index in 7 of patients with completely similar mutation spectrum were significantly lower than other patients with differential mutational landscapes between PL and MLN (p=0.019). Furthermore, KEGG pathway enrichment analysis revealed that deregulation in PI3K/AKT and Ras signaling pathway were enriched in both PL and MLN samples. More importantly, we found that aberrant activation of Proteoglycans pathway and JAK-STAT signaling, as well as aberrant HIF-1 pathway, was specifically occurred in the MLN samples, suggesting crucial roles for these signaling pathways in the involvement of lymph node metastasis. Conclusions: Our study revealed genomic heterogeneity between primary tumors and lymph nodes, and identified mutations as well as pathways that are potentially relevant to lymph node metastasis, emphasizing that such spatial heterogeneity may contribute to the evolution of the disease and result in differential responses of subsequent treatments. This study was supported by funding from National Natural Science Foundation of China (Grant No. 81602645) and Guangdong Provincial Natural Science Foundation (Grant No. 2016A030313768). Citation Format: Liao N, Zhang G, Wang Y, Guo L, Cao L, Ren C, Wen L, Li K, Jia M, Chuai S, Chen X. Spatial heterogeneity revealed by genomic profiles comparing 60 matched primary breast tumors and metastatic lymph nodes [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P4-04-05.

Clinical Utility of a Next-Generation Sequencing Panel for Acute Myeloid Leukemia Diagnostics

Next-generation sequencing (NGS) has redefined the genetic landscape of acute myeloid leukemia (AML), providing new molecular markers for diagnostic and prognostic classifications. However, its application in the clinical setting is still challenging. We hypothesized that a 19-gene AML-targeted NGS panel could be a valid approach to obtain clinically relevant information. Thus, we assessed the ability of this panel to classify AML patients according to diagnostic and prognostic indexes in a cohort of 162 patients. The assay yielded a median read depth >2000×, with 88% of on-target reads and a mean uniformity >93% without significant global strand bias. The method was sensitive and specific, with a valid performance at the clinical variant allele frequency cutoff of 3% for point mutations and 5% for insertions or deletions (INDELs). Three-hundred thirty-nine variants were found (36% INDELs and 64% single nucleotide variants). Concordance between NGS and other conventional techniques was 100%, but the NGS approach was able to identify more clinically relevant mutations. Finally, all patients could be classified into one of the 2016 World Health Organization diagnostic categories and virtually all into the recently proposed prognostic indexes (2017 European LeukemiaNet and Genomic classification). To sum up, we validate a reliable and reproducible method for AML diagnosis and demonstrate that small, well-designed NGS panels are sufficient to guide clinical decisions according to the current standards.

Unintentional Genomic Changes Endow Cupriavidus metallidurans with an Augmented Heavy-Metal Resistance.

For the past three decades, Cupriavidus metallidurans has been one of the major model organisms for bacterial tolerance to heavy metals. Its type strain CH34 contains at least 24 gene clusters distributed over four replicons, allowing for intricate and multilayered metal responses. To gain organic mercury resistance in CH34, broad-spectrum mer genes were introduced in a previous work via conjugation of the IncP-1β plasmid pTP6. However, we recently noted that this CH34-derived strain, MSR33, unexpectedly showed an increased resistance to other metals (i.e., Co2+, Ni2+, and Cd2+). To thoroughly investigate this phenomenon, we resequenced the entire genome of MSR33 and compared its DNA sequence and basal gene expression profile to those of its parental strain CH34. Genome comparison identified 11 insertions or deletions (INDELs) and nine single nucleotide polymorphisms (SNPs), whereas transcriptomic analysis displayed 107 differentially expressed genes. Sequence data implicated the transposition of IS1088 in higher Co2+ and Ni2+ resistances and altered gene expression, although the precise mechanisms of the augmented Cd2+ resistance in MSR33 remains elusive. Our work indicates that conjugation procedures involving large complex genomes and extensive mobilomes may pose a considerable risk toward the introduction of unwanted, undocumented genetic changes. Special efforts are needed for the applied use and further development of small nonconjugative broad-host plasmid vectors, ideally involving CRISPR-related and advanced biosynthetic technologies.

Comparative Genomic Analysis and Characterization of Two Salmonella enterica Serovar Enteritidis Isolates From Poultry With Notably Different Survival Abilities in Egg Whites.

Salmonella enterica serovar Enteritidis (Salmonella Enteritidis) is a globally important foodborne pathogen, and the contaminated chicken eggs are the major source of salmonellosis in humans. Salmonella Enteritidis strains are differentially susceptible to the hostile environment of egg whites. Strains with superior survival ability in egg whites are more likely to contaminate eggs and consequently infect humans. However, the genetic basis for this phenotype is unclear. We characterized two Salmonella Enteritidis strains isolated from chicken meat that had similar genetic backgrounds but large differences in survival ability in egg whites. Although genome comparisons indicated that the gene content and genomic synteny were highly conserved, variations including six insertions or deletions (INDELs) and 70 single nucleotide polymorphisms (SNPs) were observed between the two genomes. Of these, 38 variations including four INDELs and 34 non-synonymous SNPs (nsSNP) were annotated to result in amino acid substitutions or INDELs in coding proteins. These variations were located in 38 genes involved in lysozyme inhibition, vitamin biosynthesis, cell division and DNA damage response, osmotic and oxidative protection, iron-related functions, cell envelope maintenance, amino acid and carbohydrate metabolism, antimicrobial resistance, and type III secretion system. We carried out allelic replacements for two nsSNPs in bioC (biotin synthesis) and pliC (lysozyme inhibition), and two INDELs in ftsK and yqiJ (DNA damage response) by homologous recombination, and these replacements did not alter the bacterial survival ability in egg whites. However, the bacterial survival ability in egg whites was reduced when deletion mutation of the genes bioC and pliC occurred. This study provides initial correlations between observed genotypes and phenotypes and serves as an important caveat for further functional studies.

Abstract A183: Blood-based genomic profiling of cell-free tumor DNA (ctDNA) in patients with biliary tract cancer

Abstract Background: Targeted therapies are increasingly under evaluation in clinical trials for the treatment of biliary tract cancer (BTC), and cell-free tumor DNA assays are an emerging technology for the detection of actionable alterations. Methods: ctDNA analysis was performed in patients with BTC using the CLIA-certified Guardant360 liquid biopsy assay as part of routine clinical care. The assay screens up to 73 genes for single-nucleotide variants (SNVs), 23 for insertions or deletions (INDELs), 18 for copy number variations (CNVs), and 6 for fusions. Results: 855 samples were analyzed from 751 unique BTC patients. Median age was 64 years (range, 29-89), 53% were female, and 631 (84%) had at least one alteration in their first sample. In the 751 patients, the most common genes altered were TP53 (39%), KRAS (15%), PIK3CA (13%), ARID1A (13%), EGFR (11%), FGFR2 (11%), ERBB2 (11%), NF1 (10%), IDH1 (10%), APC (9%), BRAF (9%), MYC (8%), MET (7%), CCNE1 (7%), and FGFR1 (7%). Alterations in DNA damage response genes were also seen, including BRCA2 (6%), BRCA1 (5%), ATM (4%), and MLH1 (1%). The median number of alterations per sample was 3 (range, 0-40). In a clinically annotated dataset from the Massachusetts General Hospital Cancer Center, 112 samples were obtained from 61 unique patients. Among these, 52 (85%) had intrahepatic cholangiocarcinoma (ICC), 3 (5%) had extrahepatic cholangiocarcinoma, and 6 (10%) had gallbladder cancer. 20/61 (33%) patients were treated with targeted therapy. Among 20 patients with both ctDNA and tumor sequencing results, the targetable mutation was found in both ctDNA and tumor tissue in 7/20 (35%), solely in ctDNA in 1/20 (5%), and solely in tissue in 12/20 (60%) patients. The patient with the alteration detected solely in ctDNA had insufficient tissue for analysis; she was found to have an FGFR2 F276C mutation and benefited for 8.5 months from an FGFR inhibitor on a clinical trial. Of the 12 patients whose targetable mutation was not detected in plasma, 10 (83%) had an FGFR2 fusion, 1 had an INDEL in FGFR2 (Leu262_Ala266delinsAsp), and 1 had an FGFR3 splice site mutation. 15/20 (75%) patients treated with targeted therapy were followed with serial ctDNA analysis, and a potential resistance mechanism was identified in 5/15 (33%). All 5 patients had FGFR2-fusion positive ICC and developed mutations in the FGFR2 kinase domain as a potential resistance mechanism to FGFR inhibition, including the FGFR2 V564F gatekeeper mutation in 4/5 patients. Conclusions: In patients with BTC, ctDNA-based genomic profiling can detect alterations in IDH, FGFR, PIK3CA, ERBB2, BRAF, and MET. The technology is still evolving for the detection of FGFR2 fusions, which is hindered in capture-based methods in plasma by the large number of unique breakpoints and fusion partners. ctDNA analysis may also provide a noninvasive mechanism to study resistance to targeted therapy and clonal dynamics in BTC. Citation Format: Lipika Goyal, Robin Kate Kelley, Lesli Kiedrowski, Daniel Catenacci, Kabir Mody, Rachna Shroff, Aparna Parikh, Stephanie Reyes, Jordan R. Maurer, Ryan B. Corcoran, Paul Fanta, Mike Cusnir, Becky Nagy, Richard Lanman, Michael Morse, Benjamin Tan, Milind Javle, Andrew Zhu. Blood-based genomic profiling of cell-free tumor DNA (ctDNA) in patients with biliary tract cancer [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2017 Oct 26-30; Philadelphia, PA. Philadelphia (PA): AACR; Mol Cancer Ther 2018;17(1 Suppl):Abstract nr A183.

Whole Genome Sequence Analysis of Mutations Accumulated in rad27Δ Yeast Strains with Defects in the Processing of Okazaki Fragments Indicates Template-Switching Events.

Okazaki fragments that are formed during lagging strand DNA synthesis include an initiating primer consisting of both RNA and DNA. The RNA fragment must be removed before the fragments are joined. In Saccharomyces cerevisiae, a key player in this process is the structure-specific flap endonuclease, Rad27p (human homolog FEN1). To obtain a genomic view of the mutational consequence of loss of RAD27, a S. cerevisiae rad27Δ strain was subcultured for 25 generations and sequenced using Illumina paired-end sequencing. Out of the 455 changes observed in 10 colonies isolated the two most common types of events were insertions or deletions (INDELs) in simple sequence repeats (SSRs) and INDELs mediated by short direct repeats. Surprisingly, we also detected a previously neglected class of 21 template-switching events. These events were presumably generated by quasi-palindrome to palindrome correction, as well as palindrome elongation. The formation of these events is best explained by folding back of the stalled nascent strand and resumption of DNA synthesis using the same nascent strand as a template. Evidence of quasi-palindrome to palindrome correction that could be generated by template switching appears also in yeast genome evolution. Out of the 455 events, 55 events appeared in multiple isolates; further analysis indicates that these loci are mutational hotspots. Since Rad27 acts on the lagging strand when the leading strand should not contain any gaps, we propose a mechanism favoring intramolecular strand switching over an intermolecular mechanism. We note that our results open new ways of understanding template switching that occurs during genome instability and evolution.

Variation in Copy Number of MTUS1 Gene among Healthy Individuals and Cancer Patients from Gujarat

Genome variations in the form of single nucleotide polymorphism, INDELs (insertions or deletions) and, duplications, inversions and copy number variations are more widely prevalent than initially predicted. Mitochondrial tumor suppressor gene maps on chromosome 8p, in which exon 4-specific deletion is associated with susceptibility towards breast and various other forms of cancer. In this study, 41 head and neck cancer, 15 breast cancer patients and 280 healthy control individuals were analyzed for mitochondrial tumor suppressor gene copy number variation. The frequencies of wt/wt (homozygous wild-type), wt/Del (heterozygous variant) and Del/Del (homozygous deletion variant) mitochondrial tumor suppressor gene genotypes were found to be 73.3%, 26.7%, and 0% in breast cancer patients, 41.5%, 58.5%, and 0% in head and neck cancer patients and 43%, 57%, and 0% in healthy individuals, respectively. A significant association of the deletion variant with breast cancer (odds ratio = 0.27, 95% confidence interval = 0.08–0.87, P = 0.0207) was found in our population. In addition, the allele and genotype frequency varied significantly (P<0.0001) among Indian and German populations, reflecting ethnic diversity. This pilot case-control study highlighted the indicative role of mitochondrial tumor suppressor gene deletion in protection from breast cancer in Indian population. However, the findings need to be investigated in larger patient sample size before any conclusive role of mitochondrial tumor suppressor gene copy number variation on cancer risk.

Using synthetic bacterial enhancers to reveal a looping-based mechanism for quenching-like repression.

We explore a model for ‘quenching-like' repression by studying synthetic bacterial enhancers, each characterized by a different binding site architecture. To do so, we take a three-pronged approach: first, we compute the probability that a protein-bound dsDNA molecule will loop. Second, we use hundreds of synthetic enhancers to test the model's predictions in bacteria. Finally, we verify the mechanism bioinformatically in native genomes. Here we show that excluded volume effects generated by DNA-bound proteins can generate substantial quenching. Moreover, the type and extent of the regulatory effect depend strongly on the relative arrangement of the binding sites. The implications of these results are that enhancers should be insensitive to 10–11 bp insertions or deletions (INDELs) and sensitive to 5–6 bp INDELs. We test this prediction on 61 σ54-regulated qrr genes from the Vibrio genus and confirm the tolerance of these enhancers' sequences to the DNA's helical repeat.

DYRK1A haploinsufficiency causes a new recognizable syndrome with microcephaly, intellectual disability, speech impairment, and distinct facies.

Dual-specificity tyrosine-(Y)-phosphorylation-regulated kinase 1 A (DYRK1A ) is a highly conserved gene located in the Down syndrome critical region. It has an important role in early development and regulation of neuronal proliferation. Microdeletions of chromosome 21q22.12q22.3 that include DYRK1A (21q22.13) are rare and only a few pathogenic single-nucleotide variants (SNVs) in the DYRK1A gene have been described, so as of yet, the landscape of DYRK1A disruptions and their associated phenotype has not been fully explored. We have identified 14 individuals with de novo heterozygous variants of DYRK1A; five with microdeletions, three with small insertions or deletions (INDELs) and six with deleterious SNVs. The analysis of our cohort and comparison with published cases reveals that phenotypes are consistent among individuals with the 21q22.12q22.3 microdeletion and those with translocation, SNVs, or INDELs within DYRK1A. All individuals shared congenital microcephaly at birth, intellectual disability, developmental delay, severe speech impairment, short stature, and distinct facial features. The severity of the microcephaly varied from -2 SD to -5 SD. Seizures, structural brain abnormalities, eye defects, ataxia/broad-based gait, intrauterine growth restriction, minor skeletal abnormalities, and feeding difficulties were present in two-thirds of all affected individuals. Our study demonstrates that haploinsufficiency of DYRK1A results in a new recognizable syndrome, which should be considered in individuals with Angelman syndrome-like features and distinct facial features. Our report represents the largest cohort of individuals with DYRK1A disruptions to date, and is the first attempt to define consistent genotype-phenotype correlations among subjects with 21q22.13 microdeletions and DYRK1A SNVs or small INDELs.

Identification and validation of loss of function variants in clinical contexts

The choice of an appropriate variant calling pipeline for exome sequencing data is becoming increasingly more important in translational medicine projects and clinical contexts. Within GOSgene, which facilitates genetic analysis as part of a joint effort of the University College London and the Great Ormond Street Hospital, we aimed to optimize a variant calling pipeline suitable for our clinical context. We implemented the GATK/Queue framework and evaluated the performance of its two callers: the classical UnifiedGenotyper and the new variant discovery tool HaplotypeCaller. We performed an experimental validation of the loss-of-function (LoF) variants called by the two methods using Sequenom technology. UnifiedGenotyper showed a total validation rate of 97.6% for LoF single-nucleotide polymorphisms (SNPs) and 92.0% for insertions or deletions (INDELs), whereas HaplotypeCaller was 91.7% for SNPs and 55.9% for INDELs. We confirm that GATK/Queue is a reliable pipeline in translational medicine and clinical context. We conclude that in our working environment, UnifiedGenotyper is the caller of choice, being an accurate method, with a high validation rate of error-prone calls like LoF variants. We finally highlight the importance of experimental validation, especially for INDELs, as part of a standard pipeline in clinical environments.

High Resolution Melting Analysis Is a More Sensitive and Effective Alternative to Gel-Based Platforms in Analysis of SSR – An Example in Citrus

High resolution melting curve analysis (HRM) has been used as an efficient, accurate and cost-effective tool to detect single nucleotide polymorphisms (SNPs) or insertions or deletions (INDELs). However, its efficiency, accuracy and applicability to discriminate microsatellite polymorphism have not been extensively assessed. The traditional protocols used for SSR genotyping include PCR amplification of the DNA fragment and the separation of the fragments on electrophoresis-based platform. However, post-PCR handling processes are laborious and costly. Furthermore, SNPs present in the sequences flanking repeat motif cannot be detected by polyacrylamide-gel-electrophoresis based methods. In the present study, we compared the discriminating power of HRM with the traditional electrophoresis-based methods and provided a panel of primers for HRM genotyping in Citrus. The results showed that sixteen SSR markers produced distinct polymorphic melting curves among the Citrus spp investigated through HRM analysis. Among those, 10 showed more genotypes by HRM analysis than capillary electrophoresis owing to the presence of SNPs in the amplicons. For the SSR markers without SNPs present in the flanking region, HRM also gave distinct melting curves which detected same genotypes as were shown in capillary electrophoresis (CE) analysis. Moreover, HRM analysis allowed the discrimination of most of the 15 citrus genotypes and the resulting genetic distance analysis clustered them into three main branches. In conclusion, it has been approved that HRM is not only an efficient and cost-effective alternative of electrophoresis-based method for SSR markers, but also a method to uncover more polymorphisms contributed by SNPs present in SSRs. It was therefore suggested that the panel of SSR markers could be used in a variety of applications in the citrus biodiversity and breeding programs using HRM analysis. Furthermore, we speculate that the HRM analysis can be employed to analyse SSR markers in a wide range of applications in all other species.

Comparative sequence analyses of the major quantitative trait locus phosphorus uptake 1 (Pup1) reveal a complex genetic structure

The phosphorus uptake 1 (Pup1) locus was identified as a major quantitative trait locus (QTL) for tolerance of phosphorus deficiency in rice. Near-isogenic lines with the Pup1 region from tolerant donor parent Kasalath typically show threefold higher phosphorus uptake and grain yield in phosphorus-deficient field trials than the intolerant parent Nipponbare. In this study, we report the fine mapping of the Pup1 locus to the long arm of chromosome 12 (15.31-15.47 Mb). Genes in the region were initially identified on the basis of the Nipponbare reference genome, but did not reveal any obvious candidate genes related to phosphorus uptake. Kasalath BAC clones were therefore sequenced and revealed a 278-kbp sequence significantly different from the syntenic regions in Nipponbare (145 kb) and in the indica reference genome of 93-11 (742 kbp). Size differences are caused by large insertions or deletions (INDELs), and an exceptionally large number of retrotransposon and transposon-related elements (TEs) present in all three sequences (45%-54%). About 46 kb of the Kasalath sequence did not align with the entire Nipponbare genome, and only three Nipponbare genes (fatty acid alpha-dioxygenase, dirigent protein and aspartic proteinase) are highly conserved in Kasalath. Two Nipponbare genes (expressed proteins) might have evolved by at least three TE integrations in an ancestor gene that is still present in Kasalath. Several predicted Kasalath genes are novel or unknown genes that are mainly located within INDEL regions. Our results highlight the importance of sequencing QTL regions in the respective donor parent, as important genes might not be present in the current reference genomes.