Distribution Of Simple Sequence Repeats Research Articles

Complete Chloroplast Genome Sequences of Kaempferia Galanga and Kaempferia Elegans: Molecular Structures and Comparative Analysis

Kaempferia galanga and Kaempferia elegans, which belong to the genus Kaempferia family Zingiberaceae, are used as valuable herbal medicine and ornamental plants, respectively. The chloroplast genomes have been used for molecular markers, species identification and phylogenetic studies. In this study, the complete chloroplast genome sequences of K. galanga and K. elegans are reported. Results show that the complete chloroplast genome of K. galanga is 163,811 bp long, having a quadripartite structure with large single copy (LSC) of 88,405 bp and a small single copy (SSC) of 15,812 bp separated by inverted repeats (IRs) of 29,797 bp. Similarly, the complete chloroplast genome of K. elegans is 163,555 bp long, having a quadripartite structure in which IRs of 29,773 bp length separates 88,020 bp of LSC and 15,989 bp of SSC. A total of 111 genes in K. galanga and 113 genes in K. elegans comprised 79 protein-coding genes and 4 ribosomal RNA (rRNA) genes, as well as 28 and 30 transfer RNA (tRNA) genes in K. galanga and K. elegans, respectively. The gene order, GC content and orientation of the two Kaempferia chloroplast genomes exhibited high similarity. The location and distribution of simple sequence repeats (SSRs) and long repeat sequences were determined. Eight highly variable regions between the two Kaempferia species were identified and 643 mutation events, including 536 single-nucleotide polymorphisms (SNPs) and 107 insertion/deletions (indels), were accurately located. Sequence divergences of the whole chloroplast genomes were calculated among related Zingiberaceae species. The phylogenetic analysis based on SNPs among eleven species strongly supported that K. galanga and K. elegans formed a cluster within Zingiberaceae. This study identified the unique characteristics of the entire K. galanga and K. elegans chloroplast genomes that contribute to our understanding of the chloroplast DNA evolution within Zingiberaceae species. It provides valuable information for phylogenetic analysis and species identification within genus Kaempferia.

Determination of Repeat Number and Expression States of Phase-Variable Loci Through Next Generation Sequencing and Bioinformatic Analysis.

Phase variation (PV) enables high frequency, reversible switches in expression of genetic loci across numerous species of bacteria. A major mechanism of PV in bacteria is the use of slipped strand mispairing across simple sequence repeats (SSRs). The generation and online availability of genomic datasets enables a comprehensive analysis of the distribution and composition of SSRs across multiple bacterial genomes of a species. PhasomeIt is a program that was developed to rapidly identify SSRs, to determine whether these SSRs mediate PV and to find homologous PV loci across multiple genomes. We describe use of this program for analysis of neisserial genomes. We further describe a method to reassemble specific PV loci to allow analysis of large repeat tracts which are often poorly assembled due to inherent drawbacks of the Illumina next generation sequencing (NGS) platform. These methodologies allow for rapid analysis of a major mechanism of PV across numerous species of Neisseria and other bacterial species.

The complete chloroplast genome of the miracle tree Neolamarckia cadamba and its comparison in Rubiaceae family

Neolamarckia cadamba is a miracle tree species with considerable economic potential used as a timber wood and traditional medicine resource in South and Southeast Asia. To better understand the molecular basis of its chloroplast biology, we sequenced and characterised the complete chloroplast genome using Illumina pair-end sequencing. The analysis showed a chloroplast genome size of 154,999 bp in length, harbouring a pair of inverted repeats (IRs) of 25,634 bp separated by a large single copy (LSC) sequence of 85,880 bp and a small single copy (SSC) sequence of 17,851 bp. Of the 130 genes present, 96 were unique and 17 were duplicated in the IRs. The coding regions comprised 79 protein genes, 30 tRNA genes and 4 rRNA genes. In the protein-coding genes, nine genes contained one intron each, while another two genes comprised two introns. The overall GC content of the chloroplast genome was 37.6%. Simple sequence repeat (SSR) analysis revealed that most SSRs were A/T-rich, which contributed to the overall AT richness of the N. cadamba chloroplast genome. Additionally, fewer SSRs distributed in the protein-coding sequences compared to the non-coding regions, indicating an uneven distribution of SSRs within the chloroplast genome. A maximum likelihood phylogenetic analysis showed that N. cadamba was closely related to Morinda officinalis and Emmenopterys henryi, which belong to the Rubiaceae family. This complete chloroplast genome will offer valuable information for the development of highly variable DNA markers for future conservation, genetic engineering studies and variety selection of this miracle tree.

Common, Unique and Polymorphic Simple Sequence Repeats in Chloroplast Genomes of genus Arabidopsis

Simple sequence repeats (SSRs) consists of 1–6 nucleotides and are widely used molecular marker. These repeats are found in almost all organisms. However, the distribution of chloroplast SSRs (cpSSRs) is not well understood in genus A rabidopsis. To annotate the current knowledge of putative polymorphic, common, and unique cpSSRs of genus Arabidopsis, a sum of 628 cpSSRs were mined. Mononucleotides (338, 53.82%) were most abundant followed by tetranucleotides (133, 21.18%), di-nucleotides (79, 12.58%), tri-nucleotides (41, 6.53%), penta-nucleotides (19, 3.03%), and hexa-nucleotide (8, 1.27%) repeats. Apart from this, 10 compound (1.60%) cpSSRs were detected. Common, unique, and polymorphic cpSSRs were also identified. Primer pairs were designed to study cross species transferability. The cpSSRs identified in this study can be helpful in species identification, genetic mapping, and diversity studies of genus Arabidopsis.

WGSSAT: A High-Throughput Computational Pipeline for Mining and Annotation of SSR Markers From Whole Genomes.

Mining and characterization of Simple Sequence Repeat (SSR) markers from whole genomes provide valuable information about biological significance of SSR distribution and also facilitate development of markers for genetic analysis. Whole genome sequencing (WGS)-SSR Annotation Tool (WGSSAT) is a graphical user interface pipeline developed using Java Netbeans and Perl scripts which facilitates in simplifying the process of SSR mining and characterization. WGSSAT takes input in FASTA format and automates the prediction of genes, noncoding RNA (ncRNA), core genes, repeats and SSRs from whole genomes followed by mapping of the predicted SSRs onto a genome (classified according to genes, ncRNA, repeats, exonic, intronic, and core gene region) along with primer identification and mining of cross-species markers. The program also generates a detailed statistical report along with visualization of mapped SSRs, genes, core genes, and RNAs. The features of WGSSAT were demonstrated using Takifugu rubripes data. This yielded a total of 139 057 SSR, out of which 113 703 SSR primer pairs were uniquely amplified in silico onto a T. rubripes (fugu) genome. Out of 113 703 mined SSRs, 81 463 were from coding region (including 4286 exonic and 77 177 intronic), 7 from RNA, 267 from core genes of fugu, whereas 105 641 SSR and 601 SSR primer pairs were uniquely mapped onto the medaka genome. WGSSAT is tested under Ubuntu Linux. The source code, documentation, user manual, example dataset and scripts are available online at https://sourceforge.net/projects/wgssat-nbfgr.

Microsatellite Diversity and Complexity in Eighteen Staphylococcus Phage Genomes

: The present study focused on Staphylococcus phage genomes, which have been classified to 3 categories on the basis of their size. Overall, 18 classes of II Staphylococcus phage genomes with genome size around 40 kbp were investigated to elucidate the presence, distribution, and complexity of SSRs therein. The full length genome sequences from NCBI were analyzed using the IMEx software. A total of 3656 simple sequence repeats (SSRs) and 213 compound SSRs (cSSR) were present in the studied genomes. The incident frequency of SSR and cSSR per genome ranged from 183 to 308 and 8 to 19, respectively. The SSRs distribution across genomes was non-linear and so was its conversion to cSSR (the range of cSSR percentage was from 4.15 to 9.13) implicating a non-uniform incidence and clustering in genomes. The AT rich content of genomes was reflected in the prevalence of repeats with A, AT/TA, and AAG/GAA being the highest represented mono-, di-, and tri-nucleotide repeat motifs, respectively. An increase in dMAX was accompanied by greater cSSRs in the genomes yet the increase was neither uniform across genomes nor linear. The SSRs and cSSRs are predominantly localized on the coding region. The non-coding region accounts for ~ 19% in SSR and ~ 30% in cSSR while a hypothetical protein accounted for ~30% in SSRs as well as cSSR. The relative frequencies and distribution of different classes of simple and compound microsatellites within and across genomes are suggestive of these sequences being involved in genome evolution and adaptation.

Identification of Expressed Sequence Tag-simple Sequence Repeat Markers from the De Novo Transcriptome Sequence of Red Raspberry (Rubus idaeus L.)

Rubus idaeus has remarkable economic and cultural value. Developing efficient simple sequence repeat (SSR) markers is necessary for the molecular breeding of red raspberry. In this study, SSR mining was performed using the de novo transcriptome sequence of R. idaeus. In total, 14,210 SSR sequences were identified from 11,158 SSR-containing unigenes. In all the SSR sequences, mononucleotide, dinucleotide, and trinucleotide repeats were the most common, and their number and percentage were 1323 (9.31%), 6752 (47.52%), and 4897 (34.46%), respectively. Of the mononucleotide and dinucleotide repeats, A/T, AG/CT, AT/AT, and AC/GT were more abundant and accounted for 9.09%, 37.82%, 6.51%, and 3.14% of the total repeat number, respectively. In the trinucleotide, tetranucleotide, pentanucleotide, and hexanucleotide repeats, the nucleotide (NT) patterns AAG/CTT, AAAG/CTTT, AAAAG/CTTTT, and AAGAGG/CCTCTT were the most frequent, and accounted for 14.11%, 0.38%, 0.57%, and 0.23% of the total SSRs, respectively. Of the 480 SSR-containing unigenes with gene ontology (GO) annotation, the classification results showed that they were mainly involved in binding, catalytic, and transporter molecular functions. Most of the 3441 SSR-containing unigenes with the Kyoto Encyclopedia of Genes and Genomes (KEGG) annotation were involved in the following top five pathways: metabolic, RNA transport, spliceosome, protein processing in the endoplasmic reticulum, and mRNA surveillance. Thirty pairs of primers derived from the red raspberry transcriptome were randomly selected to assess their polymorphism by using 15 red raspberry germplasms, in which the polymorphism information content (PIC) values ranged from 0.50 to 0.86, with a mean of 0.73, thereby indicating a high level of polymorphism. The unweighted pair group method with arithmetic mean clustering results indicated that the thirty pairs of primers could precisely distinguish the germplasms. This study reveals the SSR distribution characteristics of red raspberry and provides a scientific basis for further genetic diversity studies and genetic linkage map construction for this species.

느타리버섯 품종 '흑타리'와 '미소'의 초위성체 특성구명

SSR은 병렬적으로 반복되는 작은 DNA서열을 말하며, 다양한 마커 기반 연구에 활용되고 있다. 국내의 주요 느타리품종인 '흑타리'와 '미소'의 유전체를 Pacbio를 이용하여 해독하였고 이 서열 정보에서 생물정보학을 이용하여 SSR을 분리하여 특성구명을 하였다. '흑타리'와 '미소' 유래 단핵균사의 유전체의 크기는 각각 40.8 Mbp와 40.3 Mbp로 밝혀졌고, 이는 사철느타리의 단핵균사 PC9과 PC15보다 컸으나, 큰느타리보다는 작았다. 총 949개와 968개의 SSR이 '흑타리'와 '미소'의 유전체 분석을 통하여 각각 검출되었다. 5개의 느타리류 유전체의 SSR 분포와 특징을 비교분석한 결과 흑타리와 미소의 SSR 갯수가 가장 많았으며, 이들의 반복서열의 분포는 다른 느타리류와 비슷한 경향을 보였다. 3-mers, 6-mers와 8-mers가 가장 발견빈도가 높은 패턴이었다. Simple sequence repeats (SSR), also referred to "microsatellites" consist of tandemly repeated short DNA sequence motifs and have been applied in various marker-based studies. SSRs were isolated and characterized from 'Heuktari' and 'Miso', which are major oyster mushroom cultivars in Korea, by genome sequencing and bioinformatic analysis. The genome sizes of 'Heuktari' and 'Miso' were estimated to be 40.8 and 40.3 Mb, respectively, which are larger than those of other P. ostreatus species (PC9 and PC10) and smaller than those of P. eryngii (KNR2312P5). In total, 949 and 968 SSRs were found in the 'Heuktari' and 'Miso' genomes, respectively. Comparative analysis of five mushrooms including P. ostreatus var. florida (PC9 and PC15) and P. eryngii revealed that the number of SSRs in 'Heuktari' and 'Miso' were the highest among them. All mushrooms studied showed similar SSR distribution patterns. Tri-, hexa-, and octanucleotide motifs accounted for the top three fractions of all SSRs.

Cytogenetic Diversity of Simple Sequences Repeats in Morphotypes of Brassica rapa ssp. chinensis.

A significant fraction of the nuclear DNA of all eukaryotes is comprised of simple sequence repeats (SSRs). Although these sequences are widely used for studying genetic variation, linkage mapping and evolution, little attention had been paid to the chromosomal distribution and cytogenetic diversity of these sequences. In this paper, we report the distribution characterization of mono-, di-, and tri-nucleotide SSRs in Brassica rapa ssp. chinensis. Fluorescence in situ hybridization was used to characterize the cytogenetic diversity of SSRs among morphotypes of B. rapa ssp. chinensis. The proportion of different SSR motifs varied among morphotypes of B. rapa ssp. chinensis, with tri-nucleotide SSRs being more prevalent in the genome of B. rapa ssp. chinensis. We determined the chromosomal locations of mono-, di-, and tri-nucleotide repeat loci. The results showed that the chromosomal distribution of SSRs in the different morphotypes is non-random and motif-dependent, and allowed us to characterize the relative variability in terms of SSR numbers and similar chromosomal distributions in centromeric/peri-centromeric heterochromatin. The differences between SSR repeats with respect to abundance and distribution indicate that SSRs are a driving force in the genomic evolution of B. rapa species. Our results provide a comprehensive view of the SSR sequence distribution and evolution for comparison among morphotypes B. rapa ssp. chinensis.

Genome-wide distribution and organization of microsatellites in six species of birds

Simple sequence repeats (SSRs), or microsatellites, are important genetic markers and play a significant role in genome organization. The genome-wide analyses of microsatellite distributions in six bird species (Gallus gallus, Meleagris gallopavo, Taeniopygia guttata, Geospiza fortis, Melopsittacus undulates, and Columba livia) were performed using in silico data mining approach. Under our search criteria, the total numbers of 1–6 bp perfect microsatellites detected ranged from 90,346 to 282,728 and covered from 0.13 to 0.49% in the complete genomes of the six bird species. The SSR abundance was not correlated with genome size, and mononucleotide repeats outnumbered other SSR categories in all of the six species examined. However, there is was a little difference in the most common repeat motifs for each length among the six different bird species considered, with obvious relation to the AT-richness of their genomes. The distribution of SSRs in the different genomic regions of three bird genomes (G. gallus, M. meleagris, and T. guttata) indicated that the intergenic regions exhibited the highest relative abundance compared to the intron and exon regions in all the six motif lengths. In the genome of G. gallus, the motif of (AGGA)n made up the most iterated microsatellite locus (spanning 108 repetitions) and 83.6% of these most abundant SSR motifs had a repeat number less than 12. What’s more, the number of microsatellites in different chromosomes was positively correlated with the size of the chromosomes in the genome of G. gallus.

Genome-Wide Comparative Analysis of Microsatellites in Pineapple

Pineapple (Ananas comosus (L.) Merrill) is the second most important tropical fruit in term of international trade. The availability of whole genomic sequences and expressed sequence tags (ESTs) offers an opportunity to identify and characterize microsatellite or simple sequence repeat (SSR) markers in pineapple. A total of 278,245 SSRs and 41,962 SSRs with an overall density of 728.57 SSRs/Mb and 619.37 SSRs/Mb were mined from genomic and ESTs sequences, respectively. 5′-untranslated regions (5′-UTRs) had the greatest amount of SSRs, 3.6–5.2 fold higher SSR density than other regions. For repeat length, 12 bp was the predominant repeat length in both assembled genome and ESTs. Class I SSRs were underrepresented compared with class II SSRs. For motif length, dinucleotide repeats were the most abundant in genomic sequences, whereas trinucleotides were the most common motif in ESTs. Tri- and hexanucleotides of total SSRs were more prevalent in ESTs than in the whole genome. The SSR frequency decreased dramatically as repeat times increased. AT was the most frequent single motif across the entire genome while AG was the most abundant motif in ESTs. Across six examined plant species, the pineapple genome displayed the highest density, substantially more than the second-place cucumber. Annotation and expression analyses were also conducted for genes containing SSRs. This thorough analysis of SSR markers in pineapple provided valuable information on the frequency and distribution of SSRs in the pineapple genome. This genomic resource will expedite genomic research and pineapple improvement.

Identification, evaluation, and application of the genomic-SSR loci in ramie

To provide a theoretical and practical foundation for ramie genetic analysis, simple sequence repeats (SSRs) were identified in the ramie genome and employed in this study. From the 115 369 sequences of a specific-locus amplified fragment library, a type of reduced representation library obtained by high-throughput sequencing, we identified 4774 sequences containing 5064 SSR motifs. SSRs of ramie included repeat motifs with lengths of 1 to 6 nucleotides, and the abundance of each motif type varied greatly. We found that mononucleotide, dinucleotide, and trinucleotide repeat motifs were the most prevalent (95.91%). A total of 98 distinct motif types were detected in the genomic-SSRs of ramie. Of them, The A/T mononucleotide motif was the most abundant, accounting for 41.45% of motifs, followed by AT/TA, accounting for 20.30%. The number of alleles per locus in 31 polymorphic microsatellite loci ranged from 2 to 7, and observed and expected heterozygosities ranged from 0.04 to 1.00 and 0.04 to 0.83, respectively. Furthermore, molecular identity cards (IDs) of the germplasms were constructed employing the ID Analysis 3.0 software. In the current study, the 26 germplasms of ramie can be distinguished by a combination of five SSR primers including Ibg5-5, Ibg3-210, Ibg1-11, Ibg6-468, and Ibg6-481. The allele polymorphisms produced by all SSR primers were used to analyze genetic relationships among the germplasms. The similarity coefficients ranged from 0.41 to 0.88. We found that these 26 germplasms were clustered into five categories using UPGMA, with poor correlation between germplasm and geographical distribution. Our study is the first large-scale SSR identification from ramie genomic sequences. We have further studied the SSR distribution pattern in the ramie genome, and proposed that it is possible to develop SSR loci from genomic data for population genetics studies, linkage mapping, quantitative trait locus mapping, cultivar fingerprinting, and as genetic diversity studies.

Genome-wide mining, characterization, and development of microsatellite markers in Marsupenaeus japonicus by genome survey sequencing

The kuruma prawn, Marsupenaeus japonicus, is one of the most cultivated and consumed species of shrimp. However, very few molecular genetic/genomic resources are publically available for it. Thus, the characterization and distribution of simple sequence repeats (SSRs) remains ambiguous and the use of SSR markers in genomic studies and marker-assisted selection is limited. The goal of this study is to characterize and develop genome-wide SSR markers in M. japonicus by genome survey sequencing for application in comparative genomics and breeding. A total of 326 945 perfect SSRs were identified, among which dinucleotide repeats were the most frequent class (44.08%), followed by mononucleotides (29.67%), trinucleotides (18.96%), tetranucleotides (5.66%), hexanucleotides (1.07%), and pentanucleotides (0.56%). In total, 151 541 SSR loci primers were successfully designed. A subset of 30 SSR primer pairs were synthesized and tested in 42 individuals from a wild population, of which 27 loci (90.0%) were successfully amplified with specific products and 24 (80.0%) were polymorphic. For the amplified polymorphic loci, the alleles ranged from 5 to 17 (with an average of 9.63), and the average PIC value was 0.796. A total of 58 256 SSR-containing sequences had significant Gene Ontology annotation; these are good functional molecular marker candidates for association studies and comparative genomic analysis. The newly identified SSRs significantly contribute to the M. japonicus genomic resources and will facilitate a number of genetic and genomic studies, including high density linkage mapping, genome-wide association analysis, marker-aided selection, comparative genomics analysis, population genetics, and evolution.

Molecular characterization and recombination analysis of an Indian isolate of Onion yellow dwarf virus

This study presents the first whole genome sequence of Onion yellow dwarf virus (OYDV isolate RR1) from onion (Allium cepa) in India along with phylogenetic and recombination studies. We examined the sequence variability, distribution of simple sequence repeats (SSRs), and recombination breakpoints of different OYDV geographical isolates. The P1 and P3 regions of OYDV show a higher rate of sequence variability in amino acid and nucleotide sequences than other genomic regions. Entropy peaks of deduced amino acid sequences were higher in both regions (P1 and P3) of different OYDVs. The observed frequency of microsatellites was also higher in the P3 region of all OYDV genomes. The Indian isolate RR1 showed 75–98 % similarity with the other OYDV isolates in nucleotide and amino acid sequences and has 43 microsatellites and two compound microsatellites. It was most closely related to garlic isolate MS/SW1 from Australia. Isolate RR1 contained six recombination breakpoints in different genomic regions with the major parent related to the MS/SW1 (Australian) and SG1 (Spanish) OYDV isolates. The phylogenetic and recombination study demonstrated the divergence of Indian isolate RR1 from OYDV isolate from Australia.

Comparative analysis of microsatellites in chloroplast genomes of lower and higher plants

Microsatellites, or simple sequence repeats (SSRs), contain repetitive DNA sequence where tandem repeats of one to six base pairs are present number of times. Chloroplast genome sequences have been shown to possess extensive variations in the length, number and distributionof SSRs. However, a comparative analysis of chloroplast microsatellites is not available. Considering their potential importance in generating genomic diversity, we have systematically analysed the abundance and distribution of simple and compound microsatellites in 164 sequenced chloroplast genomes from wide range of plants. The key findings of these studies are (1) a large number of mononucleotide repeats as compared to SSR(2-6)(di-, tri-, tetra-, penta-, hexanucleotide repeats) are present in all chloroplast genomes investigated, (2) lower plants such as algae show wide variation in relative abundance, density and distribution of microsatellite repeats as compared to flowering plants, (3) longer SSRs are excluded from coding regions of most chloroplast genomes, (4) GC content has a weak influence on number, relative abundance and relative density of mononucleotide as well as SSR(2-6). However, GC content strongly showed negative correlation with relative density (R (2)=0.5, P<0.05) and relative abundance (R (2)=0.6, P<0.05) of cSSRs. In summary, our comparative studies of chloroplast genomes illustrate the variable distribution of microsatellites and revealed that chloroplast genome of smaller plants possesses relatively more genomic diversity compared to higher plants.

Occurrence, distribution and possible functional roles of simple sequence repeats in phytoplasma genomes

Phytoplasmas are unculturable, cell-wall-less bacteria that parasitize plants and insects. This transkingdom life cycle requires rapid responses to vastly different environments, including transitions from plant phloem sieve elements to various insect tissues and alternations among diverse plant hosts. Features that enable such flexibility in other microbes include simple sequence repeats (SSRs) - mutation-prone, phase-variable short DNA tracts that function as 'evolutionary rheostats' and enhance rapid adaptations. To gain insights into the occurrence, distribution and potentially functional roles of SSRs in phytoplasmas, we performed computational analysis on the genomes of five completely sequenced phytoplasma strains, 'Candidatus Phytoplasma asteris'-related strains OYM and AYWB, 'Candidatus Phytoplasma australiense'-related strains CBWB and SLY and 'Candidatus Phytoplasma mali'-related strain AP-AT. The overall density of SSRs in phytoplasma genomes was higher than in representative strains of other prokaryotes. While mono- and trinucleotide SSRs were significantly overrepresented in the phytoplasma genomes, dinucleotide SSRs and other higher-order SSRs were underrepresented. The occurrence and distribution of long SSRs in the prophage islands and phytoplasma-unique genetic loci indicated that SSRs played a role in compounding the complexity of sequence mosaics in individual genomes and in increasing allelic diversity among genomes. Findings from computational analyses were further complemented by an examination of SSRs in varied additional phytoplasma strains, with a focus on potential contingency genes. Some SSRs were located in regions that could profoundly alter the regulation of transcription and translation of affected genes and/or the composition of protein products.

Homologous simple sequence repeats (SSRs) analysis in tetraploid (AD1) and diploid (A₂, D₅) genomes of Gossypium

Simple sequence repeats (SSRs)are a class of repetitive DNA sequences, which are commonly used for genome analysis. Comparison of the homologous SSRs among different genomes is helpful to understand the evolutionary process in relative species. In this study, SSR scanning was performed to investigate their distribution and length variation among the genomes of G. raimondii (D₅), G. arboretum (A₂) and G. hirsutum (AD₁). The results demonstrated that the distribution of SSRs in A genome was very similar with that in D genome, while the length variation of homologous SSRs between A and AD genome was more conserved than that between D and AD genome. Compared with SSRs in AD genome, the number of SSRs with longer motif length in A genome was about five times of those with shorter motif length, while it was about three times in D genome. This implied that the length variation rates of homologous SSRs between diploid cotton and tetraploid cotton were different during the parallel evolution due to the subgenome fusion, and the motif length of most SSRs in tetraoploid genome tended to become shorter than homologous SSRs in diploid genome during the process of evolution. This study comprehensively compared the SSRs in three cotton genomes and revealed the significant difference among them, providing a foundation for further evolutionary study of Gossypium genome.

Distribution and analysis of SSR in mung bean (Vigna radiata L.) genome based on an SSR-enriched library

Simple sequence repeats (SSR) are widely distributed in plant genomes, have been popular genetic markers and can be involved in gene function. We report an SSR analysis of mung bean (Vigna radiata L.), based on an SSR-enriched library. A total of 308,509 SSRs (56.9 % simple and 43.1 % compound) were discovered from 167,628 sequences. Both di- and tri-nucleotide were the most prevalent repeat types (each accounts for 48.6 %). The most frequent motifs were AAC/GTT, accounting for 45.14 % of all, followed by AC/GT at 41.80 %. After filtering the SSRs, 70,104 flanking sequences were used as BLAST queries and corresponded to 574 non-redundant gene ontology terms against the protein database from Arabidopsis thaliana. The three main categories were biological processes (23.8 %), cellular components (44.4 %) and molecular functions (31.8 %). A total of 6,100 non-repeated primer pairs were designed and validated by PCR analysis. The results showed that 60 % of primers were effective in mung bean and 35.2, 34.0 and 25.9 % could be transferred to rice bean, adzuki bean and cowpea, respectively. 9.1 % of the 6,100 displayed polymorphism between a wild and cultivated mung bean genotype, and 367 were mapped onto chromosomes using a RIL population derived from a wild × a cultivated cross. However, only 49 of 1,700 effective primer pairs showed polymorphism among 32 Chinese cultivated mung bean accessions. A total of 46,565 loci on mung bean chromosomes from the draft genome were hit by the 70,104 flanking sequences using BLASTn. The present study, especially the newly published 387 markers that have been validated and mapped, will significantly enhance genetic linkage map construction, QTL mapping and marker-assisted selection in mung bean and breeding in closely related crop species.

&amp;lt;i&amp;gt;In Silico&amp;lt;/i&amp;gt; Exploration of &amp;lt;i&amp;gt;Cannabis sativa&amp;lt;/i&amp;gt; L. Genome for Simple Sequence Repeats (SSRs)

Simple sequence repeat (SSR) or microsatellite markers, are a valuable tool for several purposes such as evaluation of genetic diversity, fingerprinting, marker assisted selection, and breeding. Recent developments in sequencing technologies and bioinformatics analyses provide new opportunity to produce a high number of less costly SSRs. Here, we used for the first time a wholegenome shotgun sequencing of the nuclear genome and transcriptome of hemp to develop microsatellite markers for C. sativa L. (hemp). Hemp is an ancient crop that is widely cultivated as a source of fiber, seeds and medicine. The analysis using the MISA program revealed a total of 407,491 SSRs (from mono-nucleotide to deca-nucleotide) in the hemp genome and 15,655 SSRs in the transcriptome. Analysis of the frequency and distribution of SSRs showed that the mono-nucleotide repeats were the most abundant (55.4%) in the genome whereas the tri-nucleotide motifs (30.4%) resulted highly predominant in the transcriptome. Poly A/T was predominant over poly G/C in both genome and transcriptome sequences. Among the tri-nucleotide repeats AAG/CTT (34.5%) resulted the most abundant in the transcriptome. Repeats larger than tri-nucleotide were also observed in the hemp genome and transcriptome. Dinucleotide and tri-nucleotide repeat expansion of 8605 and 1401 times iteration were observed however, other SSR expansion more than 387 times repetition was not found. Primers were designed for amplification of few long microsatellite sequences which could be used to identify polymorphism and to study genetic diversity among hemp cultivars.

Analysis of simple sequence repeats in mammalian cell cycle genes.

Simple sequence repeats (SSRs), or microsatellites are hyper-mutable and can lead to disorders. Here we explore SSR distribution in cell cycle-associated genes [grouped into: checkpoint; regulation; replication, repair, and recombination (RRR); and transition] in humans and orthologues of eight mammals. Among the gene groups studied, transition genes have the highest SSR density. Trinucleotide repeats are not abundant and introns have higher repeat density than exons. Many repeats in human genes are conserved; however, CG motifs are conserved only in regulation genes. SSR variability in cell cycle genes represents a genetic Achilles' heel, yet SSRs are common in all groups of genes. This tolerance many be due to i) positions in introns where they do not disrupt gene function, ii) essential roles in regulation, iii) specific value of adaptability, and/or iv) lack of negative selection pressure. Present study may be useful for further exploration of their medical relevance and potential functionality.