Sugar beet (Beta vulgaris ssp. vulgaris) is a young crop plant that originated from wild sea beet (Beta vulgaris ssp. maritima), a coastal plant native to Western and Southern Europe [1]. It has been shown that transposons have influence onto the genome structure and gene functionality of beets [2,3]. Of the many different repeats contained in a genome, only a small subset is intact and fully functional. However, this small portion may have a huge impact on the genome and as consequence on the phenotype as well. By creating alternative splicing patterns, introduction of novel promoters, change of gene regulation or simply by inactivation of gene function [4]. Thus, the genome is constantly in motion: Transposons get inserted into new positions in the genome; thereafter, selection and mutational processes act upon them. Repeats disrupting crucial functions will disappear quickly, while other elements which are neutral or even beneficial will stay on. By comparing different genomic sequence data of domesticated beets and their wild relatives, we assess the mutagenic events that took place in the beet genome in the recent evolutionary past and explore the role that transposons have played in the evolution of the beet genome. Advances in the repeat-related knowledge of the beet genome may discover new insights about recent transposon evolution and will provide a foundation for further improvements of beet as a crop plant.

Fig.1 Repetitive content of B. vulgaris spp. vulgaris, B. vulgaris ssp. maritima and B. patula, besides the assumed repetitive content of sugar beet [5].

Fig.2 Gene disruption (green) found in sugar beet, caused by a transposon insertion (orange), which disrupts gene functionality, causing rhizomania susceptibility. Sea beet (blue) RZ2 gene lacks these insertions, with results in a still functional gene, which provides rhizomania resistance [2].

[1] Dohm et al. (2014): The genome of the recently domesticated crop plant sugar beet (Beta vulgaris). Nature 505, 546-549.

[2] Capistrano-Gossmann et al. (2017): Crop wild relative populations of Beta vulgaris allow direct mapping of agronomically important genes. Nat Commun. 8: 15708.

[3] Pin et al. (2012): The role of a pseudo-response regulator gene in life cycle adaptation and domestication of beet. Curr. Biol. 22, 1095-1101.

[4] Hirsch et al. (2017): Transposable element influences on gene expression in plants. Biochimica et Biophysica Acta (BBA) - Gene Regulatory Mechanisms 1860, 157-167.

[5] Flavell et al. (1974): Genome size and the proportion of repeated nucleotide sequence DNA in plants. Biochem Genet. 12, 4, 257- 269.