LegumeSSRdb: A Comprehensive Microsatellite Marker Database of Legumes for Germplasm Characterization and Crop Improvement

Microsatellites, or simple sequence repeats (SSRs), are polymorphic loci that play a major role as molecular markers for genome analysis and plant breeding. The legume SSR database is a webserver which contains simple sequence repeats (SSRs) from genomes of 13 legume species. A total of 3,706,276 SSRs are present in the database, 698,509 of which are genic SSRs, and 3,007,772 are non-genic. This webserver is an integrated tool to perform end-to-end marker selection right from generating SSRs to designing and validating primers, visualizing the results and blasting the genomic sequences at one place without juggling between several resources. The user-friendly web interface allows users to browse SSRs based on the genomic region, chromosome, motif type, repeat motif sequence, frequency of motif, and advanced searches allow users to search based on chromosome location range and length of SSR. Users can give their desired flanking region around repeat and obtain the sequence, they can explore the genes in which the SSRs are present or the genes between which the SSRs are bound design custom primers, and perform in silico validation using PCR. An SSR prediction pipeline is implemented where the user can submit their genomic sequence to generate SSRs. This webserver will be frequently updated with more species, in time. We believe that legumeSSRdb would be a useful resource for marker-assisted selection and mapping quantitative trait loci (QTLs) to practice genomic selection and improve crop health. The database can be freely accessed at http://bioinfo.usu.edu/legumeSSRdb/.     

Genomic Resources of Three Pulsatilla Species Reveal Evolutionary Hotspots,Species-Specific Sites and Variable Plastid Structure in the Family Ranunculaceae

Background: The European continent is presently colonized by nine species of the genus Pulsatilla, five of which are encountered only in mountainous regions of southwest and south-central Europe. The remaining four species inhabit lowlands in the north-central and eastern parts of the continent. Most plants of the genus Pulsatilla are rare and endangered, which is why most research efforts focused on their biology, ecology and hybridization. The objective of this study was to develop genomic resources, including complete plastid genomes and nuclear rRNA clusters, for three sympatric Pulsatilla species that are most commonly found in Central Europe. The results will supply valuable information about genetic variation, which can be used in the process of designing primers for population studies and conservation genetics research. The complete plastid genomes together with the nuclear rRNA cluster can serve as a useful tool in hybridization studies. Methodology/principal findings: Six complete plastid genomes and nuclear rRNA clusters were sequenced from three species of Pulsatilla using the Illumina sequencing technology. Four junctions between single copy regions and inverted repeats and junctions between the identified locally-collinear blocks (LCB) were confirmed by Sanger sequencing. Pulsatilla genomes of 120 unique genes had a total length of approximately 161–162 kb, and 21 were duplicated in the inverted repeats (IR) region. Comparative plastid genomes of newly-sequenced Pulsatilla and the previously-identified plastomes of Aconitum and Ranunculus species belonging to the family Ranunculaceae revealed several variations in the structure of the genome, but the gene content remained constant. The nuclear rRNA cluster (18S-ITS1-5.8S-ITS2-26S) of studied Pulsatilla species is 5795 bp long. Among five analyzed regions of the rRNA cluster, only Internal Transcribed Spacer 2 (ITS2) enabled the molecular delimitation of closely-related Pulsatilla patens and Pulsatillavernalis. Conclusions/significance: The determination of complete plastid genome and nuclear rRNA cluster sequences in three species of the genus Pulsatilla is an important contribution to our knowledge of the evolution and phylogeography of those endangered taxa. The resulting data can be used to identify regions that are particularly useful for barcoding, phylogenetic and phylogeographic studies. The investigated taxa can be identified at each stage of development based on their species-specific SNPs. The nuclear and plastid genomic resources enable advanced studies on hybridization, including identification of parent species, including their roles in that process. The identified nonsynonymous mutations could play an important role in adaptations to changing environments. The results of the study will also provide valuable information about the evolution of the plastome structure in the family Ranunculaceae.