Comparative assessment of EST-SSR, EST-SNP and AFLP markers for evaluation of genetic diversity and conservation of genetic resources using wild, cultivated and elite barleys

A set of 16 expressed sequence tag (EST)-derived simple sequence repeat (SSR) and 15 EST-derived single nucleotide polymorphism (SNP) markers together with 4 amplified fragment length polymorphism (AFLP) primer combinations were analyzed on 43 wild (Hordeum vulgare ssp. spontaneum – HS), 35 cultivated (H. vulgare ssp. vulgare – HV) and 12 elite (H. vulgare ssp. vulgare – from EU) barley lines. SSR markers were found most polymorphic with an average PIC value of 0.593 and eight alleles per marker, while AFLP markers showed the highest effective multiplex ratio (26.4) and marker index (5.042). The effective marker index (EMI) was recorded highest (0.468) for AFLP markers and lowest (0.341) for the SNP markers while the SSR markers had an intermediate EMI (0.442). Cluster analysis on combined set of SSR, SNP and AFLP genotyping data classified wild, cultivated and elite barley lines in three distinct groups. The present study suggests the SNP markers as the best class of markers for characterizing and conserving the genebank materials and the AFLP and SSR markers more suitable for diversity analysis and fingerprinting

Identification and characterization of expressed sequence tags-derived simple sequence repeats markers from robusta coffee variety 'CxR' (an interspecific hybrid of Coffea canephora x Coffea congensis)

SSR (simple sequence repeats) markers derived from ESTs (expressed sequence tags), commonly called EST-SSRs or genic SSRs provide useful genetic markers for crop improvement. These are easy and economical to develop as by-products of large-scale EST resources that have become available as part of the functional genomic studies in many plant species. Here, we describe for the first time, nine genic-SSRs of coffee that are developed from the microsatellite containing ESTs from a cDNA library of moisture-stressed leaves of coffee variety, ‘CxR’ (a commercial interspecific hybrid between Coffea congensis and Coffea canephora). The markers show considerable allelic diversity with PIC values up to 0.70 and 0.75 for Coffea arabica and Coffea canephora, respectively, and robust cross-species amplification in 16 other related taxa of coffee. The validation studies thus demonstrate the potential utility of the EST-SSRs for genetic analysis of coffee germplasm

Identification, characterization and utilization of EST-derived genic microsatellite markers for genome analyses of coffee and related species

Genic microsatellites or EST–SSRs derived from expressed sequence tags (ESTs) are desired because these are inexpensive to develop, represent transcribed genes, and often a putative function can be assigned to them. In this study we investigated 2,553 coffee ESTs (461 from the public domain and 2,092 in-house generated ESTs) for identification and development of genic microsatellite markers. Of these, 2,458 ESTs (all >100 bp in size) were searched for SSRs using MISA—search module followed by stackPACK clustering that revealed a total of 425 microsatellites in 331 (13.5%) non-redundant ESTs/consensus sequences suggesting an approximate frequency of 1 SSR/2.16 kb of the analysed coffee transcriptome. Identified microsatellites mainly comprised of di-/tri-nucleotide repeats, of which repeat motifs AG and AAG were the most abundant. A total of 224 primer pairs could be designed from the non-redundant SSR-positive ESTs (excluding those with only mononucleotide repeats) for possible use as potential genic markers. Of this set, a total of 24 (10%) primer pairs were tested and 18 could be validated as usable markers. Sixteen of these markers revealed moderate to high polymorphism information content (PIC) across 23 genotypes of C. arabica and C. canephora, while 2 markers were found to be monomorphic. All the markers also showed robust cross-species amplifications across 14 Coffea and 4 Psilanthus species. The apparent broad cross-species/genera transferability was further confirmed by cloning and sequencing of the amplified alleles. Thus, the study provides an insight about the frequency and distribution of SSRs in coffee transcriptome, and also demonstrates the successful development of genic-SSRs. It is expected that the potential markers described here would add to the repertoire of DNA markers needed for genetic studies in cultivated coffee and also related taxa that constitute the important secondary genepool for coffee improvement

Draft Genomes of Two Artocarpus Plants, Jackfruit (A. heterophyllus) and Breadfruit (A. altilis)

Two of the most economically important plants in the Artocarpus genus are jackfruit (A. heterophyllus Lam.) and breadfruit (A. altilis (Parkinson) Fosberg). Both species are long-lived trees that have been cultivated for thousands of years in their native regions. Today they are grown throughout tropical to subtropical areas as an important source of starch and other valuable nutrients. There are hundreds of breadfruit varieties that are native to Oceania, of which the most commonly distributed types are seedless triploids. Jackfruit is likely native to the Western Ghats of India and produces one of the largest tree-borne fruit structures (reaching up to 45 kg). To-date, there is limited genomic information for these two economically important species. Here, we generated 273 Gb and 227 Gb of raw data from jackfruit and breadfruit, respectively. The high-quality reads from jackfruit were assembled into 162,440 scaffolds totaling 982 Mb with 35,858 genes. Similarly, the breadfruit reads were assembled into 180,971 scaffolds totaling 833 Mb with 34,010 genes. A total of 2822 and 2034 expanded gene families were found in jackfruit and breadfruit, respectively, enriched in pathways including starch and sucrose metabolism, photosynthesis, and others. The copy number of several starch synthesis-related genes were found to be increased in jackfruit and breadfruit compared to closely-related species, and the tissue-specific expression might imply their sugar-rich and starch-rich characteristics. Overall, the publication of high-quality genomes for jackfruit and breadfruit provides information about their specific composition and the underlying genes involved in sugar and starch metabolism

The genome of Gynandropsis gynandra provides insights into whole-genome duplications and the evolution of C4 photosynthesis in Cleomaceae

Gynandropsis gynandra (Cleomaceae) is a cosmopolitan leafy vegetable and medicinal plant, which has also been used as a model to study C4 photosynthesis due to its evolutionary proximity to Arabidopsis. Here, we present a high-quality genome sequence of G. gynandra, anchored onto 17 main super- scaffolds with a total length of 740 Mb, an N50 of 42 Mb and 30,933 well-supported gene models. The G. gynandra genome and previously released genomes of C3 relatives in the Cleomaceae and Brassicaceae make an excellent model for studying the role of genome evolution in the transition from C3 to C4 photosynthesis. We revealed that G. gynandra and its C3 relative Tarenaya hassleriana shared a whole-genome duplication event (Gg-α), then an addition of a third genome (Th-α, +1x) took place in T. hassleriana but not in G. gynandra. Analysis of syntenic copy number of C4 photosynthesis-related gene families indicates that G. gynandra generally retained more duplicated copies of these genes than C3 T. hassleriana, and also that the G. gynandra C4 genes might have been under positive selection pressure. Both whole-genome and single-gene duplication were found to contribute to the expansion of the aforementioned gene families in G. gynandra. Collectively, this study enhances our understanding of the impact of gene duplication and gene retention on the evolution of C4 photosynthesis in Cleomaceae

Status of perennial tree germplasm resources in India and their utilization in the context of global genome sequencing efforts

Tree species are characterized by their perennial growth habit, woody morphology, long juvenile period phase, mostly outcrossing behaviour, highly heterozygosity genetic makeup, and relatively high genetic diversity. The economically important trees have been an integral part of the human life system due to their provision of timber, fruit, fodder, and medicinal and/or health benefits. Despite its widespread application in agriculture, industrial and medicinal values, the molecular aspects of key economic traits of many tree species remain largely unexplored. Over the past two decades, research on forest tree genomics has generally lagged behind that of other agronomic crops. Genomic research on trees is motivated by the need to support genetic improvement programmes mostly for food trees and timber, and develop diagnostic tools to assist in recommendation for optimum conservation, restoration and management of natural populations. Research on long-lived woody perennials is extending our molecular knowledge and understanding of complex life histories and adaptations to the environment, enriching a field that has traditionally drawn its biological inference from a few short-lived herbaceous species. These concerns have fostered research aimed at deciphering the genomic basis of complex traits that are related to the adaptive value of trees. This review summarizes the highlights of tree genomics and offers some priorities for accelerating progress in the next decade

Chromosome evolution and the genetic basis of agronomically important traits in greater yam

The nutrient-rich tubers of the greater yam Dioscorea alata L. provide food and income security for millions of people around the world. Despite its global importance, however, greater yam remains an “orphan crop.” Here we address this resource gap by presenting a highly-contiguous chromosome-scale genome assembly of greater yam combined with a dense genetic map derived from African breeding populations. The genome sequence reveals an ancient lineage-specific genome duplication, followed by extensive genome-wide reorganization. Using our new genomic tools we find quantitative trait loci for susceptibility to anthracnose, a damaging fungal pathogen of yam, and several tuber quality traits. Genomic analysis of breeding lines reveals both extensive inbreeding as well as regions of extensive heterozygosity that may represent interspecific introgression during domestication. These tools and insights will enable yam breeders to unlock the potential of this staple crop and take full advantage of its adaptability to varied environments