A new set of universal de novo sequencing primers for extensive coverage of noncoding chloroplast DNA: new opportunities for phylogenetic studies and cpSSR discovery

We present a new set of universal de novo sequencing primers targeting noncoding chloroplast DNA. The set of 107 polymerase chain reaction (PCR) primers span approximately 86% of the noncoding nucleotides in the large single copy region of Nicotiana tabacum, Oryza sativa and the orchid Phalaenopsis aphrodite. PCR tests confirmed the primers are effective in a wide range of monocots and dicots. More than 19.5 kb of cpDNA sequence was obtained across representative orchid genera with up to 82 chloroplast simple sequence repeats (cpSSRs) detected per genus. This primer set will facilitate both phylogenetic studies and rapid discovery of cpSSRs for plants, such as orchids, where there are limited genomic resources.     

Development,cross-species/genera transferability of novel EST-SSR markers and their utility in revealing population structure and genetic diversity in sugarcane

Sugarcane (Saccharum spp. hybrid) with complex polyploid genome requires a large number of informative DNA markers for various applications in genetics and breeding. Despite the great advances in genomic technology, it is observed in several crop species, especially in sugarcane, the availability of molecular tools such as microsatellite markers are limited. Now-a-days EST-SSR markers are preferred to genomic SSR (gSSR) as they represent only the functional part of the genome, which can be easily associated with desired trait. The present study was taken up with a new set of 351 EST-SSRs developed from the 4085 non redundant EST sequences of two Indian sugarcane cultivars. Among these EST-SSRs, TNR containing motifs were predominant with a frequency of 51.6%. Thirty percent EST-SSRs showed homology with annotated protein. A high frequency of SSRs was found in the 5′UTR and in the ORF (about 27%) and a low frequency was observed in the 3′UTR (about 8%). Two hundred twenty-seven EST-SSRs were evaluated, in sugarcane, allied genera of sugarcane and cereals, and 134 of these have revealed polymorphism with a range of PIC value 0.12 to 0.99. The cross transferability rate ranged from 87.0% to 93.4% in Saccharum complex, 80.0% to 87.0% in allied genera, and 76.0% to 80.0% in cereals. Cloning and sequencing of EST-SSR size variant amplicons revealed that the variation in the number of repeat-units was the main source of EST-SSR fragment polymorphism. When 124 sugarcane accessions were analyzed for population structure using model-based approach, seven genetically distinct groups or admixtures thereof were observed in sugarcane. Results of principal coordinate analysis or UPGMA to evaluate genetic relationships delineated also the 124 accessions into seven groups. Thus, a high level of polymorphism adequate genetic diversity and population structure assayed with the EST-SSR markers not only suggested their utility in various applications in genetics and genomics in sugarcane but also enriched the microsatellite marker resources in sugarcane.     

Molecular genetic diversity of Punica granatum L. (pomegranate) as revealed by microsatellite DNA markers (SSR)

Pomegranate (Punica granatum L.) is one of the oldest known edible fruits and more and more it arouse interest of scientific community given its numerous biological activities. However, information about its genetic resources and characterization using reliable molecular markers are still scarce. In the present study, we report the development of 4 new polymorphic SSR markers. They have been used in addition to 11 SSRs previously published to investigate molecular diversity of 33 P. granatum ecotypes. Based on the multi-locus profiles, twenty-two distinctive genotypes were identified. Globally, quite low genetic diversity has been revealed, as measured by allele richness (2.83 per locus) and heterozygosity (He = 0.245; Ho = 0.243), reflecting the narrow genetic background of the plant material. Four synonymous groups could be detected involving 15 accessions. Results of ordination and cluster analysis suggested that almost all the Tunisian cultivars share similar genetic background, and are likely derived from a small number of introductions in ancient times. Results issued from this study provide essential information to project a pomegranate core-collection without plant material duplication and for sustainable management of pomegranate landraces at national and international level. Furthermore, these SSR markers are powerful tool for marker assisted selection (MAS) program and for QTL studies.