Genome-wide characterization of microsatellites in Triticeae species: abundance, distribution and evolution

TriticeaeSSRdb: a comprehensive database of simple sequence repeats in Triticeae

Microsatellites, known as simple sequence repeats (SSRs), are short tandem repeats of 1 to 6 nucleotide motifs found in all genomes, particularly eukaryotes. They are widely used as co-dominant markers in genetic analyses and molecular breeding. Triticeae, a tribe of grasses, includes major cereal crops such as bread wheat, barley, and rye, as well as abundant forage and lawn grasses, playing a crucial role in global food production and agriculture. To enhance genetic work and expedite the improvement of Triticeae crops, we have developed TriticeaeSSRdb, an integrated and user-friendly database. It contains 3,891,705 SSRs from 21 species and offers browsing options based on genomic regions, chromosomes, motif types, and repeat motif sequences. Advanced search functions allow personalized searches based on chromosome location and length of SSR. Users can also explore the genes associated with SSRs, design customized primer pairs for PCR validation, and utilize practical tools for whole-genome browsing, sequence alignment, and in silico SSR prediction from local sequences. We continually update TriticeaeSSRdb with additional species and practical utilities. We anticipate that this database will greatly facilitate trait genetic analyses and enhance molecular breeding strategies for Triticeae crops. Researchers can freely access the database at http://triticeaessrdb.com/.

The Triticeae CBF Gene Cluster-To Frost Resistance and Beyond

The pivotal role of CBF/DREB1 transcriptional factors in Triticeae crops involved in the abiotic stress response has been highlighted. The CBFs represent an important hub in the ICE-CBF-COR pathway, which is one of the most relevant mechanisms capable of activating the adaptive response to cold and drought in wheat, barley, and rye. Understanding the intricate mechanisms and regulation of the cluster of CBF genes harbored by the homoeologous chromosome group 5 entails significant potential for the genetic improvement of small grain cereals. Triticeae crops seem to share common mechanisms characterized, however, by some peculiar aspects of the response to stress, highlighting a combined landscape of single-nucleotide variants and copy number variation involving CBF members of subgroup IV. Moreover, while chromosome 5 ploidy appears to confer species-specific levels of resistance, an important involvement of the ICE factor might explain the greater tolerance of rye. By unraveling the genetic basis of abiotic stress tolerance, researchers can develop resilient varieties better equipped to withstand extreme environmental conditions. Hence, advancing our knowledge of CBFs and their interactions represents a promising avenue for improving crop resilience and food security.

CRISPR/Cas9 Editing Sites Identification and Multi-Elements Association Analysis in Camellia sinensis

CRISPR/Cas9 is an efficient genome-editing tool, and the identification of editing sites and potential influences in the Camellia sinensis genome have not been investigated. In this study, bioinformatics methods were used to characterise the Camellia sinensis genome including editing sites, simple sequence repeats (SSRs), G-quadruplexes (GQ), gene density, and their relationships. A total of 248,134,838 potential editing sites were identified in the genome, and five PAM types, AGG, TGG, CGG, GGG, and NGG, were observed, of which 66,665,912 were found to be specific, and they were present in all structural elements of the genes. The characteristic region of high GC content, GQ density, and PAM density in contrast to low gene density and SSR density was identified in the chromosomes in the joint analysis, and it was associated with secondary metabolites and amino acid biosynthesis pathways. CRISPR/Cas9, as a technology to drive crop improvement, with the identified editing sites and effector elements, provides valuable tools for functional studies and molecular breeding in Camellia sinensis.

Genetic Diversity and Population Structure in Türkiye Bread Wheat Genotypes Revealed by Simple Sequence Repeats (SSR) Markers

Wheat genotypes should be improved through available germplasm genetic diversity to ensure food security. This study investigated the molecular diversity and population structure of a set of Türkiye bread wheat genotypes using 120 microsatellite markers. Based on the results, 651 polymorphic alleles were evaluated to determine genetic diversity and population structure. The number of alleles ranged from 2 to 19, with an average of 5.44 alleles per locus. Polymorphic information content (PIC) ranged from 0.031 to 0.915 with a mean of 0.43. In addition, the gene diversity index ranged from 0.03 to 0.92 with an average of 0.46. The expected heterozygosity ranged from 0.00 to 0.359 with a mean of 0.124. The unbiased expected heterozygosity ranged from 0.00 to 0.319 with an average of 0.112. The mean values of the number of effective alleles (Ne), genetic diversity of Nei (H) and Shannon's information index (I) were estimated at 1.190, 1.049 and 0.168, respectively. The highest genetic diversity (GD) was estimated between genotypes G1 and G27. In the UPGMA dendrogram, the 63 genotypes were grouped into three clusters. The three main coordinates were able to explain 12.64, 6.38 and 4.90% of genetic diversity, respectively. AMOVA revealed diversity within populations at 78% and between populations at 22%. The current populations were found to be highly structured. Model-based cluster analyses classified the 63 genotypes studied into three subpopulations. The values of F-statistic (Fst) for the identified subpopulations were 0.253, 0.330 and 0.244, respectively. In addition, the expected values of heterozygosity (He) for these sub-populations were recorded as 0.45, 0.46 and 0.44, respectively. Therefore, SSR markers can be useful not only in genetic diversity and association analysis of wheat but also in its germplasm for various agronomic traits or mechanisms of tolerance to environmental stresses.

Characterization of Simple Sequence Repeat (SSR) Markers Mined in Whole Grape Genomes

SSR (simple sequence repeat) DNA markers are widely used for genotype DNA identification, QTL mapping, and analyzing genetic biodiversity. However, SSRs in grapes are still in their early stages, with a few primer pairs accessible. With the whole-genome sequencing (WGS) of several grape varieties, characterization of grape SSR changed to be necessary not only to genomics but to also help SSR development and utility. Based on this, we identified the whole-genome SSR of nine grape cultivars (‘PN40024’, ‘Cabernet Sauvignon’, ‘Carménère’, ‘Chardonnay’, ‘Merlot’, ‘Riesling’, ‘Zinfandel’, ‘Shine Muscat’, and ‘Muscat Hamburg’) with whole-genome sequences released publicly and found that there are great differences in the distribution of SSR loci in different varieties. According to the difference in genome size, the number of SSRs ranged from 267,385 (Cabernet Sauvignon) to 627,429 (Carménère), the density of the SSR locus in the genome of nine cultivars was generally 1 per Kb. SSR motif distribution characteristic analysis of these grape cultivars showed that the distribution patterns among grape cultivars were conservative, mainly enriched in A/T. However, there are some differences in motif types (especially tetranucleotides, pentanucleotides, and hexanucleotides), quantity, total length, and average length in different varieties, which might be related to the size of the assembled genome or the specificity of variety domestication. The distribution characteristics of SSRs were revealed by whole-genome analysis of simple repeats of grape varieties. In this study, 32 pairs of primers with lower polymorphism have been screened, which provided an important research foundation for the development of molecular markers of grape variety identification and the construction of linkage maps of important agronomic traits for crop improvement.

Cytogenetic identification and molecular marker development of a novel wheat-Leymus mollis 4Ns(4D) alien disomic substitution line with resistance to stripe rust and Fusarium head blight

Leymus mollis (Trin.) Pilg. (2n = 4x = 28, NsNsXmXm) potentially harbours useful genes that might contribute to the improvement of wheat. We describe M862 as a novel wheat-L. mollis alien disomic substitution line from a cross between wheat cv. 7182 and octoploid Tritileymus M47. Cytological observations indicate that M862 has a chromosome constitution of 2n = 42 = 21II. Two 4D chromosomes of wheat substituted by two L. mollis Ns chromosomes were observed, using the GISH and ND-FISH analyses. Molecular marker, 55K SNP array and wheat-P. huashanica liquid array (GenoBaits^®WheatplusPh) analyses further indicate that the alien chromosomes are L. mollis 4Ns. Therefore, it was deduced that M862 was a wheat-L. mollis 4Ns(4D) alien disomic substitution line. There were also changes in chromosomes 1A, 1D, 2B and 5A detected by ND-FISH analysis. Transcriptome sequencing showed that the structural variation of 1D, 1A and 5A may have smaller impact on gene expression than that for 2B. In addition, a total of 16 markers derived from Lm#4Ns were developed from transcriptome sequences, and these proved to be highly effective for tracking the introduced chromosome. M862 showed reduced height, larger grains (weight and width), and was highly resistance to CYR32 and CYR34 stripe rust races at the seedling stage and mixed stripe rust races (CYR32, CYR33 and CYR34) at the adult stage. It was also resistance to Fusarium head blight (FHB). This alien disomic substitution line M862 may be exploited as an important genetic material in the domestication of stipe rust and FHB resistance wheat varieties.

A Pipeline for the Development of Microsatellite Markers using Next Generation Sequencing Data

Background: Also known as Simple Sequence Repetitions (SSRs), microsatellites are profoundly informative molecular markers and powerful tools in genetics and ecology studies on plants. Objective: This research presents a workflow for developing microsatellite markers using genome skimming. Methods: The pipeline was proposed in several stages that must be performed sequentially: obtaining DNA sequences, identifying microsatellite regions, designing primers, and selecting candidate microsatellite regions to develop the markers. Our pipeline efficiency was analyzed using Illumina sequencing data from the non-model tree species Pterodon emarginatus Vog. Results: The pipeline revealed 4,382 microsatellite regions and drew 7,411 pairs of primers for P. emarginatus. However, a much larger number of microsatellite regions with the potential to develop markers were discovered from our pipeline. We selected 50 microsatellite regions with high potential for developing markers and organized 29 microsatellite regions in sets for multiplex PCR. Conclusion: The proposed pipeline is a powerful tool for fast and efficient development of microsatellite markers on a large scale in several species, especially nonmodel plant species.

Rapid Genome-Wide Location-Specific Polymorphic SSR Marker Discovery in Black Pepper by GBS Approach

Black pepper (Piper nigrum), the "King of Spices," is an economically important spice in India and is known for its medicinal and cultural values. SSRs, the tandem repeats of small DNA sequences, are often polymorphic in nature with diverse applications. For population structure, QTL/gene discovery, MAS, and diversity analysis, it is imperative to have their location specificity. The existing PinigSSRdb catalogs ~70K putative SSR markers but these are anonymous (unknown chromosomal location), based on 916 scaffolds rather than 26 chromosomes. Under this study, we generated ddRAD sequence data of 29 black pepper genotypes from all over India, being low-cost and most efficient technique for the identification of polymorphic markers. The major limitation of ddRAD with compromised/non-uniform coverage has been successfully overcome by taking advantage of chromosome-wise data availability. The latest black pepper genome assembly was used to extract genome-wide SSRs. A total of 276,230 genomic SSRs were mined distributed over 26 chromosomes, with relative density of 362.88 SSRs/Mb and average distance of 2.76 Kb between two SSRs. This assembly was also used to find the polymorphic SSRs in the generated GBS data of 29 black pepper genotypes utilizing rapid and cost-effective method giving 3,176 polymorphic SSRs, out of which 2015 were found to be hypervariable. The developed web-genomic resource, BlackP2MSATdb (http://webtom.cabgrid.res.in/blackp2msatdb/), is the largest and first reported web resource for genomic and polymorphic SSRs of black pepper, which is useful to develop varietal signature, coreset, physical map, QTL/gene identification, and MAS in endeavor of black pepper production.

Genome-wide simple sequence repeat markers in potato: abundance, distribution, composition, and polymorphism

Simple sequence repeats (SSRs) are important sources of genetic diversity and are widely used as markers in genetics and molecular breeding. In this study, we examined four potato genomes of DM1-3 516 R44 (DM) from Solanum phureja, RH89039-16 (RH) from Solanum tuberosum, M6 from Solanum chacoense and Solanum commersonii to determine SSR abundance and distribution and develop a larger list of polymorphic markers for a potentially wide range of uses for the potato community. A total of 1,734,619 SSRs were identified across the four genomes with an average of 433,655 SSRs per genome and 2.31kb per SSR. The most abundant repeat units for mono-, di-, tri-, and tetra-nucleotide SSRs were (A/T)n, (AT/AT)n, (AAT/ATT)n, and (ATAT/ATAT)n, respectively. The SSRs were most abundant (78.79%) in intergenic regions and least abundant (3.68%) in untranslated regions. On average, 168,069 SSRs with unique flanking sequences were identified in the four genomes. Further, we identified 16,245 polymorphic SSR markers among the four genomes. Experimental validation confirmed 99.69% of tested markers could generate target bands. The high-density potato SSR markers developed in this study will undoubtedly facilitate the application of SSR markers for genetic research and marker-pyramiding in potato breeding.

Genome-wide characterization of simple sequence repeats in Palmae genomes

Background

Microsatellites or simple sequence repeats (SSRs) have become the most significant DNA marker technology used in genetic research. The availability of complete draft genomes for a number of Palmae species has made it possible to perform genome-wide analysis of SSRs in these species. Palm trees are tropical and subtropical plants with agricultural and economic importance due to the nutritional value of their fruit cultivars.

Objective

This is the first comprehensive study examining and comparing microsatellites in completely-sequenced draft genomes of Palmae species.

Methods

We identified and compared perfect SSRs with 1–6 bp nucleotide motifs to characterize microsatellites in Palmae species using PERF v0.2.5. We analyzed their relative abundance, relative density, and GC content in five palm species: Phoenix dactylifera, Cocos nucifera, Calamus simplicifolius, Elaeis oleifera, and Elaeis guineensis.

Results

A total of 118241, 328189, 450753, 176608, and 70694 SSRs were identified, respectively. The six repeat types were not evenly distributed across the five genomes. Mono- and dinucleotide SSRs were the most abundant, and GC content was highest in tri- and hexanucleotide SSRs.

Conclusion

We envisage that this analysis would further substantiate more in-depth computational, biochemical, and molecular studies on the roles SSRs may play in the genome organization of the palm species. The current study contributes a detailed characterization of simple sequence repeats in palm genomes.

Electronic supplementary material

The online version of this article (10.1007/s13258-020-00924-w) contains supplementary material, which is available to authorized users.

Detection and application of genome-wide variations in peach for association and genetic relationship analysis

BACKGROUND

Peach (Prunus persica L.) is a diploid species and model plant of the Rosaceae family. In the past decade, significant progress has been made in peach genetic research via DNA markers, but the number of these markers remains limited.

RESULTS

In this study, we performed a genome-wide DNA markers detection based on sequencing data of six distantly related peach accessions. A total of 650,693~1,053,547 single nucleotide polymorphisms (SNPs), 114,227~178,968 small insertion/deletions (InDels), 8386~12,298 structure variants (SVs), 2111~2581 copy number variants (CNVs) and 229,357~346,940 simple sequence repeats (SSRs) were detected and annotated. To demonstrate the application of DNA markers, 944 SNPs were filtered for association study of fruit ripening time and 15 highly polymorphic SSRs were selected to analyze the genetic relationship among 221 accessions.

CONCLUSIONS

The results showed that the use of high-throughput sequencing to develop DNA markers is fast and effective. Comprehensive identification of DNA markers, including SVs and SSRs, would be of benefit to genetic diversity evaluation, genetic mapping, and molecular breeding of peach.

Genome-wide identification of microsatellite markers from cultivated peanut (Arachis hypogaea L.)

Background

Microsatellites, or simple sequence repeats (SSRs), represent important DNA variations that are widely distributed across the entire plant genome and can be used to develop SSR markers, which can then be used to conduct genetic analyses and molecular breeding. Cultivated peanut (A. hypogaea L.), an important oil crop worldwide, is an allotetraploid (AABB, 2n = 4× = 40) plant species. Because of its complex genome, genomic marker development has been very challenging. However, sequencing of cultivated peanut genome allowed us to develop genomic markers and construct a high-density physical map.

Results

A total of 8,329,496 SSRs were identified, including 3,772,653, 4,414,961, and 141,882 SSRs that were distributed in subgenome A, B, and nine scaffolds, respectively. Based on the flanking sequences of the identified SSRs, a total of 973,984 newly developed SSR markers were developed in subgenome A (462,267), B (489,394), and nine scaffolds (22,323), with an average density of 392.45 markers per Mb. In silico PCR evaluation showed that an average of 88.32% of the SSR markers generated only one in silico-specific product in two tetraploid A. hypogaea varieties, Tifrunner and Shitouqi. A total of 39,599 common SSR markers were identified among the two A. hypogaea varieties and two progenitors, A. duranensis and A. ipaensis. Additionally, an amplification effectiveness of 44.15% was observed by real PCR validation. Moreover, a total of 1276 public SSR loci were integrated with the newly developed SSR markers. Finally, a previously known leaf spot quantitative trait locus (QTL), qLLS_T13_A05_7, was determined to be in a 1.448-Mb region on chromosome A05. In this region, a total of 819 newly developed SSR markers were located and 108 candidate genes were detected.

Conclusions

The availability of these newly developed and public SSR markers both provide a large number of molecular markers that could potentially be used to enhance the process of trait genetic analyses and improve molecular breeding strategies for cultivated peanut.

Molecular genotyping, diversity studies and high-resolution molecular markers unveiled by microsatellites in Giardia duodenalis

BACKGROUND

Giardia duodenalis (synonyms G. lamblia and G. intestinalis) is an enteric protozoan parasite of a wide range of mammalian hosts, including humans and various domestic and wild animals. There is considerable genetic variability in G. duodenalis and isolates of this parasite have been divided into eight genetic assemblages. Microsatellites markers can be used to discriminate isolates with a high level of sensitivity. This study was conducted to identify and characterize genomic microsatellites (simple sequence repeats-SSRs), sequences of one- to six-nucleotide motifs repeated in tandem, present in the available genomes of G. duodenalis and to develop new markers that can serve as a tool for detection and for characterizing the genetic diversity of this parasite.

METHODOLOGY/ PRINCIPAL FINDINGS

For each genetic assemblage, polymorphism levels for the microsatellite markers were evaluated. After performing the analysis using the MISA and SciRoKo software, 1,853 simple sequence repeats (SSRs) were identified. In all the genomes, trinucleotide repeats were the most common class followed by tetranucleotide. Many of the SSR loci are assemblage-specific, and 36 SSR loci shared among all the genomes were identified. Together with hypothetical proteins, variant-specific surface proteins represented nearly half of the annotated SSR loci. The results regarding the most common repeat among the SSRs led us to infer that positive selection occurred to avoid frameshift mutations. Additionally, based on inter- and intra-genetic assemblages polymorphism analyses, we unveiled previously undetected genetic variation, indicating that the microsatellite markers we developed are useful molecular tools for epidemiological inferences based on population genetics patterns and processes.

CONCLUSIONS

There is increasing demand for the development of new molecular markers and for the characterization of pathogens at a higher resolution level. In this study, we present 60 G. duodenalis microsatellites markers that exhibited high polymerase chain reaction (PCR) amplification efficiency among the different genetic assemblages. Twenty of these markers presented nucleotide sequence polymorphisms and may be used as a genotyping tool. The monomorphic markers can be used for the detection of the parasite at the species and genetic assemblage level. These polymorphic markers revealed a genetic diversity that was previously undetectable, thus they can be considered valuable molecular tools for high resolution markers in future studies investigating Giardia and may also be used for epidemiological inferences based on populations genetics patterns and processes.

Genome-wide characterization of microsatellites and genetic diversity assessment of spinach in the Chinese germplasm collection

Spinach is a nutritional leafy green vegetable, and it also serves as a model species for studying sex chromosome evolution. Genetic marker development and genome structure analysis are important in breeding practice and theoretical evolution studies of spinach. In this study, the frequency and distribution of different microsatellites in the recently released draft spinach genome were characterized. A total of 261,002 perfect microsatellites were identified (estimated frequency: ~262.1 loci/Mbp). The most abundant microsatellites were tetranucleotide and trinucleotide, accounting for 33.2% and 27.7% of the total number of microsatellites, respectively. A total of 105 primer pairs were designed and screened, and 34 were polymorphic among the detected spinach cultivars. Combined with seven primer sets developed previously, 41 primer pairs were used to investigate genetic diversity among 43 spinach cultivars in China. The average polymorphism information content value of the 41 markers was 0.43, representing an intermediate level. The spinach cultivars had a low genetic diversity, and no detectable common factors were shared by each group in the UPGMA dendrogram. This study's findings facilitate further investigations on the organization of the microsatellites in spinach genome and provide clues for future breeding applications of spinach in China.

Putative Microsatellite DNA Marker-Based Wheat Genomic Resource for Varietal Improvement and Management

Wheat fulfills 20% of global caloric requirement. World needs 60% more wheat for 9 billion population by 2050 but climate change with increasing temperature is projected to affect wheat productivity adversely. Trait improvement and management of wheat germplasm requires genomic resource. Simple Sequence Repeats (SSRs) being highly polymorphic and ubiquitously distributed in the genome, can be a marker of choice but there is no structured marker database with options to generate primer pairs for genotyping on desired chromosome/physical location. Previously associated markers with different wheat trait are also not available in any database. Limitations of in vitro SSR discovery can be overcome by genome-wide in silico mining of SSR. Triticum aestivum SSR database (TaSSRDb) is an integrated online database with three-tier architecture, developed using PHP and MySQL and accessible at http://webtom.cabgrid.res.in/wheatssr/. For genotyping, Primer3 standalone code computes primers on user request. Chromosome-wise SSR calling for all the three sub genomes along with choice of motif types is provided in addition to the primer generation for desired marker. We report here a database of highest number of SSRs (476,169) from complex, hexaploid wheat genome (~17 GB) along with previously reported 268 SSR markers associated with 11 traits. Highest (116.93 SSRs/Mb) and lowest (74.57 SSRs/Mb) SSR densities were found on 2D and 3A chromosome, respectively. To obtain homozygous locus, e-PCR was done. Such 30 loci were randomly selected for PCR validation in panel of 18 wheat Advance Varietal Trial (AVT) lines. TaSSRDb can be a valuable genomic resource tool for linkage mapping, gene/QTL (Quantitative trait locus) discovery, diversity analysis, traceability and variety identification. Varietal specific profiling and differentiation can supplement DUS (Distinctiveness, Uniformity, and Stability) testing, EDV (Essentially Derived Variety)/IV (Initial Variety) disputes, seed purity and hybrid wheat testing. All these are required in germplasm management as well as also in the endeavor of wheat productivity.

Large-scale analysis reveals that the genome features of simple sequence repeats are generally conserved at the family level in insects

BACKGROUND

Simple sequence repeats (SSR), also called microsatellites, have been widely used as genetic markers, and have been extensively studied in some model insects. At present, the genomes of more than 100 insect species are available. However, the features of SSRs in most insect genomes remain largely unknown.

RESULTS

We identified 15.01 million SSRs across 136 insect genomes. The number of identified SSRs was positively associated with genome size in insects, but the frequency and density per megabase of genomes were not. Most insect SSRs (56.2-93.1%) were perfect (no mismatch). Imperfect (at least one mismatch) SSRs (average length 22-73 bp) were longer than perfect SSRs (16-30 bp). The most abundant insect SSRs were the di- and trinucleotide types, which accounted for 27.2% and 22.0% of all SSRs, respectively. On average, 59.1%, 36.8%, and 3.7% of insect SSRs were located in intergenic, intronic, and exonic regions, respectively. The percentages of various types of SSRs were similar among insects from the same family. However, they were dissimilar among insects from different families within orders. We carried out a phylogenetic analysis using the SSR frequencies. Species from the same family were generally clustered together in the evolutionary tree. However, insects from the same order but not in the same family did not cluster together. These results indicated that although SSRs undergo rapid expansions and contractions in different populations of the same species, the general genomic features of insect SSRs remain conserved at the family level.

CONCLUSION

Millions of insect SSRs were identified and their genome features were analyzed. Most insect SSRs were perfect and were located in intergenic regions. We presented evidence that the variance of insect SSRs accumulated after the differentiation of insect families.

Genome-Wide Discovery of Microsatellite Markers from Diploid Progenitor Species, Arachis duranensis and A. ipaensis, and Their Application in Cultivated Peanut (A. hypogaea)

Despite several efforts in the last decade toward development of simple sequence repeat (SSR) markers in peanut, there is still a need for more markers for conducting different genetic and breeding studies. With the effort of the International Peanut Genome Initiative, the availability of reference genome for both the diploid progenitors of cultivated peanut allowed us to identify 135,529 and 199,957 SSRs from the A (Arachis duranensis) and B genomes (Arachis ipaensis), respectively. Genome sequence analysis showed uneven distribution of the SSR motifs across genomes with variation in parameters such as SSR type, repeat number, and SSR length. Using the flanking sequences of identified SSRs, primers were designed for 51,354 and 60,893 SSRs with densities of 49 and 45 SSRs per Mb in A. duranensis and A. ipaensis, respectively. In silico PCR analysis of these SSR markers showed high transferability between wild and cultivated Arachis species. Two physical maps were developed for the A genome and the B genome using these SSR markers, and two reported disease resistance quantitative trait loci (QTLs), qF2TSWV5 for tomato spotted wilt virus (TSWV) and qF2LS6 for leaf spot (LS), were mapped in the 8.135 Mb region of chromosome A04 of A. duranensis. From this genomic region, 719 novel SSR markers were developed, which provide the possibility for fine mapping of these QTLs. In addition, this region also harbors 652 genes and 49 of these are defense related genes, including two NB-ARC genes, three LRR receptor-like genes and three WRKY transcription factors. These disease resistance related genes could contribute to resistance to viral (such as TSWV) and fungal (such as LS) diseases in peanut. In summary, this study not only provides a large number of molecular markers for potential use in peanut genetic map development and QTL mapping but also for map-based gene cloning and molecular breeding.

Enabling Molecular Technologies for Trait Improvement in Wheat

Wheat is the major staple food crop and a source of calories for humans worldwide. A steady increase in the wheat production is essential to meet the demands of an ever-increasing global population and to achieve food security. The large size and structurally intricate genome of polyploid wheat had hindered the genomic analysis. However, with the advent of new genomic technologies such as next generation sequencing has led to genome drafts for bread wheat and its progenitors and has paved the way to design new strategies for crop improvement. Here we provide an overview of the advancements made in wheat genomics together with the available "omics approaches" and bioinformatics resources developed for wheat research. Advances in genomic, transcriptomic, and metabolomic technologies are highlighted as options to circumvent existing bottlenecks in the phenotypic and genomic selection and gene transfer. The contemporary reverse genetics approaches, including the novel genome editing techniques to inform targeted manipulation of a single/multiple genes and strategies for generating marker-free transgenic wheat plants, emphasize potential to revolutionize wheat improvement shortly.

Genome-Wide Analysis of Simple Sequence Repeats in Bitter Gourd (Momordica charantia)

Bitter gourd (Momordica charantia) is widely cultivated as a vegetable and medicinal herb in many Asian and African countries. After the sequencing of the cucumber (Cucumis sativus), watermelon (Citrullus lanatus), and melon (Cucumis melo) genomes, bitter gourd became the fourth cucurbit species whose whole genome was sequenced. However, a comprehensive analysis of simple sequence repeats (SSRs) in bitter gourd, including a comparison with the three aforementioned cucurbit species has not yet been published. Here, we identified a total of 188,091 and 167,160 SSR motifs in the genomes of the bitter gourd lines 'Dali-11' and 'OHB3-1,' respectively. Subsequently, the SSR content, motif lengths, and classified motif types were characterized for the bitter gourd genomes and compared among all the cucurbit genomes. Lastly, a large set of 138,727 unique in silico SSR primer pairs were designed for bitter gourd. Among these, 71 primers were selected, all of which successfully amplified SSRs from the two bitter gourd lines 'Dali-11' and 'K44'. To further examine the utilization of unique SSR primers, 21 SSR markers were used to genotype a collection of 211 bitter gourd lines from all over the world. A model-based clustering method and phylogenetic analysis indicated a clear separation among the geographic groups. The genomic SSR markers developed in this study have considerable potential value in advancing bitter gourd research.