A single molecule scaffold for the maize genome.

About 85% of the maize genome consists of highly repetitive sequences that are interspersed by low-copy, gene-coding sequences. The maize community has dealt with this genomic complexity by the construction of an integrated genetic and physical map (iMap), but this resource alone was not sufficient for ensuring the quality of the current sequence build. For this purpose, we constructed a genome-wide, high-resolution optical map of the maize inbred line B73 genome containing >91,000 restriction sites (averaging 1 site/ approximately 23 kb) accrued from mapping genomic DNA molecules. Our optical map comprises 66 contigs, averaging 31.88 Mb in size and spanning 91.5% (2,103.93 Mb/ approximately 2,300 Mb) of the maize genome. A new algorithm was created that considered both optical map and unfinished BAC sequence data for placing 60/66 (2,032.42 Mb) optical map contigs onto the maize iMap. The alignment of optical maps against numerous data sources yielded comprehensive results that proved revealing and productive. For example, gaps were uncovered and characterized within the iMap, the FPC (fingerprinted contigs) map, and the chromosome-wide pseudomolecules. Such alignments also suggested amended placements of FPC contigs on the maize genetic map and proactively guided the assembly of chromosome-wide pseudomolecules, especially within complex genomic regions. Lastly, we think that the full integration of B73 optical maps with the maize iMap would greatly facilitate maize sequence finishing efforts that would make it a valuable reference for comparative studies among cereals, or other maize inbred lines and cultivars.

Shotgun optical mapping of the entire Leishmania major Friedlin genome.

Leishmania is a group of protozoan parasites which causes a broad spectrum of diseases resulting in widespread human suffering and death, as well as economic loss from the infection of some domestic animals and wildlife. To further understand the fundamental genomic architecture of this parasite, and to accelerate the on-going sequencing project, a whole-genome XbaI restriction map was constructed using the optical mapping system. This map supplemented traditional physical maps that were generated by fingerprinting and hybridization of cosmid and P1 clone libraries. Thirty-six optical map contigs were constructed for the corresponding known 36 chromosomes of the Leishmania major Friedlin genome. The chromosome sizes ranged from 326.9 to 2821.3 kb, with a total genome size of 34.7 Mb; the average XbaI restriction fragment was 25.3 kb, and ranged from 15.7 to 77.8 kb on a per chromosomes basis. Comparison between the optical maps and the in silico maps of sequence drawn from completed, nearly finished, or large sequence contigs showed that optical maps served several useful functions within the path to create finished sequence by: guiding aspects of the sequence assembly, identifying misassemblies, detection of cosmid or PAC clones misplacements to chromosomes, and validation of sequence stemming from varying degrees of finishing. Our results also showed the potential use of optical maps as a means to detect and characterize map segmental duplication within genomes.