Zea mays cultivar:K0326Y Genome sequencing and assembly. Zea mays cultivar:K0326Y

The most abundant storage proteins in maize endosperm are prolamins, called zeins, which are deficient in the essential amino acid lysine, requiring costly dietary supplementation. A natural high-lysine variant lacks the Opaque2 (O2) bZIP transcription factor that regulates the expression of most zein genes. In the o2 mutant, the amount of zein proteins is dramatically reduced, balanced by an increase of non-zein proteins, thereby doubling the lysine levels of total protein compared to normal maize. However, the chalky and soft endosperm texture of o2 prevents the transport and storage of large quantities, mostly due to fungal infections. To circumvent such problems, a long-term breeding effort has achieved the restoration of kernel hardness over the o2 mutation with the introduction of Quantitative Trait Loci (QTLs), distinguished as Quality Protein Maize (QPM). QPM has now been produced in many developing countries, where people consume maize as the sole protein source. However, mechanisms of o2 modification factors are complex and of different impact. The main challenge is how to introduce multiple non-linked o2 modifiers from tropical germplasm into temperate inbred lines, still retaining a homozygous recessive o2 background. Given the enormous sequence variation of maize genomes, a single inbred genome sequence cannot substitute as a reference for such complex breeding projects as QPM, rendering the development of new QPM lines to different location a slow process. To accelerate such efforts and to understand the basis of the chromosomal context, we applied a whole-genome sequencing approach with long sequence reads to a QPM line to allow for a more detailed genomic analysis.