Transposable elements contribute to dynamic genome content in maize

Transposable elements (TEs) are ubiquitous components of eukaryotic genomes and can create variation in genomic organization. The majority of maize genomes are composed of TEs. We developed an approach to define shared and variable TE insertions across genome assemblies and applied this method to four maize genomes (B73, W22, Mo17, and PH207). Among these genomes we identified 1.6 Gb of variable TE sequence representing a combination of recent TE movement and deletion of previously existing TEs. Although recent TE movement only accounted for a portion of the TE variability, we identified 4,737 TEs unique to one genome with defined insertion sites in all other genomes. Variable TEs are found for all superfamilies and are distributed across the genome, including in regions of recent shared ancestry among individuals. There are 2,380 genes annotated in the B73 genome located within variable TEs, providing evidence for the role of TEs in contributing to the substantial differences in gene content among these genotypes. The large scope of TE variation present in this limited sample of temperate maize genomes highlights the major contribution of TEs in driving variation in genome organization and gene content. Significance Statement The majority of the maize genome is comprised of transposable elements (TEs) that have the potential to create genomic variation within species. We developed a method to identify shared and non-shared TEs using whole genome assemblies of four maize inbred lines. Variable TEs are found throughout the maize genome and in comparisons of any two genomes we find ~20% of the genome is due to non-shared TEs. Several thousand maize genes are found within TEs that are variable across lines, highlighting the contribution of TEs to gene content variation. This study creates a comprehensive resource for genomic studies of TE variability among four maize genomes, which will enable studies on the consequences of variable TEs on genome function.

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