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      Simple Sequence Repeat Polymorphisms (SSRPs) for Evaluation of Molecular Diversity and Germplasm Classification of Minor Crops

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          Abstract

          Evaluation of the genetic diversity among populations is an essential prerequisite for the preservation of endangered species. Thousands of new accessions are introduced into germplasm institutes each year, thereby necessitating assessment of their molecular diversity before elimination of the redundant genotypes. Of the protocols that facilitate the assessment of molecular diversity, SSRPs (simple sequence repeat polymorphisms) or microsatellite variation is the preferred system since it detects a large number of DNA polymorphisms with relatively simple technical complexity. The paucity of information on DNA sequences has limited their widespread utilization in the assessment of genetic diversity of minor or neglected crop species. However, recent advancements in DNA sequencing and PCR technologies in conjunction with sophisticated computer software have facilitated the development of SSRP markers in minor crops. This review examines the development and molecular nature of SSR markers, and their utilization in many aspects of plant genetics and ecology.

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          Most cited references122

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          Exploiting EST databases for the development and characterization of gene-derived SSR-markers in barley (Hordeum vulgare L.).

          A software tool was developed for the identification of simple sequence repeats (SSRs) in a barley ( Hordeum vulgare L.) EST (expressed sequence tag) database comprising 24,595 sequences. In total, 1,856 SSR-containing sequences were identified. Trimeric SSR repeat motifs appeared to be the most abundant type. A subset of 311 primer pairs flanking SSR loci have been used for screening polymorphisms among six barley cultivars, being parents of three mapping populations. As a result, 76 EST-derived SSR-markers were integrated into a barley genetic consensus map. A correlation between polymorphism and the number of repeats was observed for SSRs built of dimeric up to tetrameric units. 3'-ESTs yielded a higher portion of polymorphic SSRs (64%) than 5'-ESTs did. The estimated PIC (polymorphic information content) value was 0.45 +/- 0.03. Approximately 80% of the SSR-markers amplified DNA fragments in Hordeum bulbosum, followed by rye, wheat (both about 60%) and rice (40%). A subset of 38 EST-derived SSR-markers comprising 114 alleles were used to investigate genetic diversity among 54 barley cultivars. In accordance with a previous, RFLP-based, study, spring and winter cultivars, as well as two- and six-rowed barleys, formed separate clades upon PCoA analysis. The results show that: (1) with the software tool developed, EST databases can be efficiently exploited for the development of cDNA-SSRs, (2) EST-derived SSRs are significantly less polymorphic than those derived from genomic regions, (3) a considerable portion of the developed SSRs can be transferred to related species, and (4) compared to RFLP-markers, cDNA-SSRs yield similar patterns of genetic diversity.
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            A draft sequence of the rice genome (Oryza sativa L. ssp. indica).

            J. Yu (2002)
            We have produced a draft sequence of the rice genome for the most widely cultivated subspecies in China, Oryza sativa L. ssp. indica, by whole-genome shotgun sequencing. The genome was 466 megabases in size, with an estimated 46,022 to 55,615 genes. Functional coverage in the assembled sequences was 92.0%. About 42.2% of the genome was in exact 20-nucleotide oligomer repeats, and most of the transposons were in the intergenic regions between genes. Although 80.6% of predicted Arabidopsis thaliana genes had a homolog in rice, only 49.4% of predicted rice genes had a homolog in A. thaliana. The large proportion of rice genes with no recognizable homologs is due to a gradient in the GC content of rice coding sequences.
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              Genic microsatellite markers in plants: features and applications.

              Expressed sequence tag (EST) projects have generated a vast amount of publicly available sequence data from plant species; these data can be mined for simple sequence repeats (SSRs). These SSRs are useful as molecular markers because their development is inexpensive, they represent transcribed genes and a putative function can often be deduced by a homology search. Because they are derived from transcripts, they are useful for assaying the functional diversity in natural populations or germplasm collections. These markers are valuable because of their higher level of transferability to related species, and they can often be used as anchor markers for comparative mapping and evolutionary studies. They have been developed and mapped in several crop species and could prove useful for marker-assisted selection, especially when the markers reside in the genes responsible for a phenotypic trait. Applications and potential uses of EST-SSRs in plant genetics and breeding are discussed.
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                Author and article information

                Journal
                Molecules
                Molecules
                molecules
                Molecules
                Molecular Diversity Preservation International
                1420-3049
                10 November 2009
                November 2009
                : 14
                : 11
                : 4546-4569
                Affiliations
                [1 ] Department of Plant Sciences, Kongju National University, Yesan 340-702, Korea
                [2 ] Division of Bio-Resources Technology, Kangwon National University, Chunchon 200-701, Korea
                [3 ] Department of Molecular Biosciences, Kangwon National University, Chunchon 200-701, Korea
                [4 ] Institute of Biosciences and Biotechnology, Kangwon National University, Chunchon 200-701, Korea
                Author notes
                [* ] Author to whom correspondence should be addressed; E-Mail: kimnamsu@ 123456kangwon.ac.kr
                Article
                molecules-14-04546
                10.3390/molecules14114546
                6255041
                19924085
                be036100-6122-41a9-a064-49292e8602aa
                © 2009 by the authors;

                licensee Molecular Diversity Preservation International, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution license ( http://creativecommons.org/licenses/by/3.0/).

                History
                : 13 September 2009
                : 05 November 2009
                : 10 November 2009
                Categories
                Review

                genetic diversity,germplasm,dna polymorphism,molecular markers,ssr

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