Expanding the BonnMu sequence-indexed repository of transposon induced maize (Zea mays L.) mutations in dent and flint germplasm

The BonnMu resource is a transposon-tagged mutant collection designed for functional genomics studies in maize. To expand this resource, we crossed an active Mutator (Mu) line with dent (B73, Co125) and flint (DK105, EP1 and F7) germplasm, resulting in the generation of 8,064 mutagenized BonnMu F2-families. Sequencing of these Mu-tagged families revealed 425,924 heritable Mu insertions affecting 36,612 (83%) of the 44,303 high-confidence gene models of maize (B73v5). On average, we observed 12 Mu insertions per gene (425,924 total insertions/ 36,612 affected genes) and 53 insertions per BonnMu F2-family (425,924 total insertions/ 8,064 families). Mu insertions and photos of seedling phenotypes from segregating BonnMu F2-families can be accessed through the Maize Genetics and Genomics Database (MaizeGDB). Downstream examination via the automated Mutant-seq Workflow Utility (MuWU) identified 94% of the germinal insertion sites in genic regions and only a small fraction of 6% inserting in non-coding intergenic sequences of the genome. Consistently, Mu insertions aligned with gene-dense chromosomal arms. In total, 42% of all BonnMu insertions were located in the 5 untranslated region (UTR) of genes, corresponding to accessible chromatin. Furthermore, for 38% of the insertions (163,843 of 425,924 total insertions) Mu1, Mu8 and MuDR were confirmed to be the causal Mu elements. Our publicly accessible European BonnMu resource has archived insertions covering two major germplasm groups, thus facilitating both forward and reverse genetics studies.