Development of genomic microsatellites in Gleditsia triacanthos (Fabaceae) using Illumina sequencing

Repetitive genomic elements in Campomanesia xanthocarpa: prospection, characterization and cross amplification of molecular markers

Repetitive genomic elements were prospected in Campomanesia xanthocarpa, aiming to characterize these elements in a non-model plant species and to develop species-specific microsatellite markers. Approximately 4.12% of the partial genome of C. xanthocarpa is composed of repetitive elements, being retrotransposons the most widely represented. A total of nine polymorphic microsatellite markers were obtained: four nuclear-neutral, two nuclear EST, two plastidial and one mitochondrial. Levels of population genetic diversity of four natural populations of C. xanthocarpa were characterized using these markers. In addition, the cross-species amplification of the microsatellite markers was tested in seven species of tribe Myrteae (Myrtaceae). The characterized microsatellite markers revealed low to moderate levels of genetic diversity (expected heterozygosity range: 0.33-0.57; observed heterozygosity: 0.26-0.74 and number of alleles: 2.25-4.25). Cross-species amplification was successful for all loci, except Cxant76. These nine markers will contribute for studies on genetic diversity, gene flow, plant selection and breeding of this species, towards the conservation of natural populations, as well as its commercial use.

Optimizing depth and type of high-throughput sequencing data for microsatellite discovery

PREMISE

Simple sequence repeat (SSR) markers (microsatellites) are a mainstay of many labs, especially when working on a limited budget, carrying out preliminary analyses, and in teaching. Whether SSRs mined from plant genomes or transcriptomes are preferred for certain applications, and the depth of sequencing needed to allow efficient SSR discovery, has not been tested.

METHODS

I used genome and transcriptome high-throughput sequencing data at a range of sequencing depths to compare efficacy of SSR identification. I then tested primers from tomato for amplification, polymorphism, and transferability to related species.

RESULTS

Small assemblies (two million read pairs) identified ca. 200-2000 potential markers from the genome assemblies and ca. 600-3650 from the transcriptome assemblies. Genome-derived contigs were often short, potentially precluding primer design. Genomic SSR primers were less transferable across species but exhibited greater variation (partially explained by being composed of more repeat units) than transcriptome-derived primers.

DISCUSSION

Small high-throughput sequencing resources may be sufficient for identification of hundreds of SSRs. Genomic data may be preferable in species with low polymorphism, but transcriptome data may result in longer loci (more amenable to primer design) and primers may be more transferable to related species.

Characterization of Plastidial and Nuclear SSR Markers for Understanding Invasion Histories and Genetic Diversity of Schinus molle L

Invasive plant species are expected to display high dispersal capacity but low levels of genetic diversity due to the founder effect occurring at each invasion episode. Understanding the history of invasions and the levels of genetic diversity of such species is an important task for planning management and monitoring strategy for these events. Peruvian Peppertree (Schinus molle L.) is a pioneer tree species native from South America which was introduced in North America, Europe and Africa, becoming a threat to these non-native habitats. In this study, we report the discovery and characterization of 17 plastidial (ptSSR) and seven nuclear (nSSR) markers for S. molle based on low-coverage whole-genome sequencing data acquired through next-generation sequencing. The markers were tested in 56 individuals from two natural populations sampled in the Brazilian Caatinga and Pampa biomes. All loci are moderately to highly polymorphic and revealed to be suitable for genetic monitoring of new invasions, for understanding the history of old invasions, as well as for genetic studies of native populations in their natural occurrence range and of orchards established with commercial purposes.

Microsatellite markers: what they mean and why they are so useful

Microsatellites or Single Sequence Repeats (SSRs) are extensively employed in plant genetics studies, using both low and high throughput genotyping approaches. Motivated by the importance of these sequences over the last decades this review aims to address some theoretical aspects of SSRs, including definition, characterization and biological function. The methodologies for the development of SSR loci, genotyping and their applications as molecular markers are also reviewed. Finally, two data surveys are presented. The first was conducted using the main database of Web of Science, prospecting for articles published over the period from 2010 to 2015, resulting in approximately 930 records. The second survey was focused on papers that aimed at SSR marker development, published in the American Journal of Botany's Primer Notes and Protocols in Plant Sciences (over 2013 up to 2015), resulting in a total of 87 publications. This scenario confirms the current relevance of SSRs and indicates their continuous utilization in plant science.

Preliminary Genomic Characterization of Ten Hardwood Tree Species from Multiplexed Low Coverage Whole Genome Sequencing

Forest health issues are on the rise in the United States, resulting from introduction of alien pests and diseases, coupled with abiotic stresses related to climate change. Increasingly, forest scientists are finding genetic/genomic resources valuable in addressing forest health issues. For a set of ten ecologically and economically important native hardwood tree species representing a broad phylogenetic spectrum, we used low coverage whole genome sequencing from multiplex Illumina paired ends to economically profile their genomic content. For six species, the genome content was further analyzed by flow cytometry in order to determine the nuclear genome size. Sequencing yielded a depth of 0.8X to 7.5X, from which in silico analysis yielded preliminary estimates of gene and repetitive sequence content in the genome for each species. Thousands of genomic SSRs were identified, with a clear predisposition toward dinucleotide repeats and AT-rich repeat motifs. Flanking primers were designed for SSR loci for all ten species, ranging from 891 loci in sugar maple to 18,167 in redbay. In summary, we have demonstrated that useful preliminary genome information including repeat content, gene content and useful SSR markers can be obtained at low cost and time input from a single lane of Illumina multiplex sequence.