Zea mays Genome sequencing and assembly

Zea mays (maize) has the highest world-wide production of all grain crops, yielding 875 million tonnes in 2012 (http://faostat.fao.org/). Although a food staple in many regions of the world, most is used for animal feed and ethanol fuel. Maize was domesticated from wild teosinte in Central America and its cultivation spread throughout the Americas by Pre-Columbian civilizations. In addition to its economic value, maize is an important model organism for studies in plant genetics, physiology, and development. It has a large genome of of about 2.4 gigabases with a haploid chromosome number of 10 (Schnable et al., 2009; Zhang et al., 2009). Maize is distinguished from other grasses in that its genome arose from an ancient tetraploidy event unique to its lineage. The maize B73 reference genome has been revised three times since its initial release as a BAC-by-BAC assembly in 2009 (Schnable et al., 2009). This entirely new assembly of the maize genome (B73 RefGen_v4) is constructed from PacBio Single Molecule Real-Time (SMRT) sequencing at approximately 60-fold coverage and scaffolded with the aid of a high-resolution whole-genome restriction (optical) mapping. The pseudomolecules of maize B73 RefGen_v4 are assembled nearly end-to-end, representing a 52-fold improvement in average contig size relative to the previous reference (B73 RefGen_v3).