Genomic tools development for Aquilegia: construction of a BAC-based physical map.

BACKGROUND: The genus Aquilegia, consisting of approximately 70 taxa, is a member of the basal eudicot lineage, Ranuculales, which is evolutionarily intermediate between monocots and core eudicots, and represents a relatively unstudied clade in the angiosperm phylogenetic tree that bridges the gap between these two major plant groups. Aquilegia species are closely related and their distribution covers highly diverse habitats. These provide rich resources to better understand the genetic basis of adaptation to different pollinators and habitats that in turn leads to rapid speciation. To gain insights into the genome structure and facilitate gene identification, comparative genomics and whole-genome shotgun sequencing assembly, BAC-based genomics resources are of crucial importance. RESULTS: BAC-based genomic resources, including two BAC libraries, a physical map with anchored markers and BAC end sequences, were established from A. formosa. The physical map was composed of a total of 50,155 BAC clones in 832 contigs and 3939 singletons, covering 21X genome equivalents. These contigs spanned a physical length of 689.8 Mb (~2.3X of the genome) suggesting the complex heterozygosity of the genome. A set of 197 markers was developed from ESTs induced by drought-stress, or involved in anthocyanin biosynthesis or floral development, and was integrated into the physical map. Among these were 87 genetically mapped markers that anchored 54 contigs, spanning 76.4 Mb (25.5%) across the genome. Analysis of a selection of 12,086 BAC end sequences (BESs) from the minimal tiling path (MTP) allowed a preview of the Aquilegia genome organization, including identification of transposable elements, simple sequence repeats and gene content. Common repetitive elements previously reported in both monocots and core eudicots were identified in Aquilegia suggesting the value of this genome in connecting the two major plant clades. Comparison with sequenced plant genomes indicated a higher similarity to grapevine (Vitis vinifera) than to rice and Arabidopsis in the transcriptomes. CONCLUSIONS: The A. formosa BAC-based genomic resources provide valuable tools to study Aquilegia genome. Further integration of other existing genomics resources, such as ESTs, into the physical map should enable better understanding of the molecular mechanisms underlying adaptive radiation and elaboration of floral morphology.

A blackberry (Rubus L.) expressed sequence tag library for the development of simple sequence repeat markers.

BACKGROUND: The recent development of novel repeat-fruiting types of blackberry (Rubus L.) cultivars, combined with a long history of morphological marker-assisted selection for thornlessness by blackberry breeders, has given rise to increased interest in using molecular markers to facilitate blackberry breeding. Yet no genetic maps, molecular markers, or even sequences exist specifically for cultivated blackberry. The purpose of this study is to begin development of these tools by generating and annotating the first blackberry expressed sequence tag (EST) library, designing primers from the ESTs to amplify regions containing simple sequence repeats (SSR), and testing the usefulness of a subset of the EST-SSRs with two blackberry cultivars. RESULTS: A cDNA library of 18,432 clones was generated from expanding leaf tissue of the cultivar Merton Thornless, a progenitor of many thornless commercial cultivars. Among the most abundantly expressed of the 3,000 genes annotated were those involved with energy, cell structure, and defense. From individual sequences containing SSRs, 673 primer pairs were designed. Of a randomly chosen set of 33 primer pairs tested with two blackberry cultivars, 10 detected an average of 1.9 polymorphic PCR products. CONCLUSION: This rate predicts that this library may yield as many as 940 SSR primer pairs detecting 1,786 polymorphisms. This may be sufficient to generate a genetic map that can be used to associate molecular markers with phenotypic traits, making possible molecular marker-assisted breeding to compliment existing morphological marker-assisted breeding in blackberry.

New resources for marine genomics: bacterial artificial chromosome libraries for the Eastern and Pacific oysters (Crassostrea virginica and C. gigas).

Large-insert genomic bacterial artificial chromosome (BAC) libraries of two culturally and economically important oyster species, Crassostrea virginica and C. gigas, have been developed as part of an international effort to develop tools and reagents that will advance our ability to conduct genetic and genomic research. A total of 73,728 C. gigas clones with an average insert size of 152 kb were picked and arrayed representing an 11.8-fold genome coverage. A total of 55,296 clones with an average insert size of 150 kb were picked and arrayed for C. virginica, also representing an 11.8-fold genome coverage. The C. gigas and C. virginica libraries were screened with probes derived from selected oyster genes using high-density BAC colony filter arrays. The probes identified 4 to 25 clones per gene for C. virginica and 5 to 50 clones per gene for C. gigas. We conducted a preliminary analysis of genetic polymorphism represented in the C. gigas library. The results suggest that the degree of divergence among similar sequences is highly variable and concentrated in intronic regions. Evidence supporting allelic polymorphism is reported for two genes and allelic and/or locus specific polymorphism for several others. Classical inheritance studies are needed to confirm the nature of these polymorphisms. The oyster BAC libraries are publicly available to the research community on a cost-recovery basis at (www.genome.clemson.edu).

Pulsed-field gel electrophoresis for long-range restriction mapping.

This unit describes procedures for generating long-range restriction maps of genomic DNA and for analysis of large insert clones. The basic protocol details restriction digestion of agarose-embedded DNA, PFGE separation, Southern transfer, and hybridization. Support protocols describe the preparation of high-molecular-weight genomic DNA samples in agarose blocks and in agarose microbeads, respectively. Additional support protocols describe the preparation of DNA size standards from l phage and two yeast species, Saccharomyces cerevisiae and Schizosaccharomyces pombe. An alternative method of preparing S. cerevisiae size standards using lithium dodecyl sulfate (LiDS) solubilization is provided. The final protocol details the preparation of BAC DNA suitable for digestion, mapping, and sequencing.