An Update on the Sugar Beet Genome and Its Annotation

Sugar beet (Beta vulgaris ssp. vulgaris) is a diploid plant with n=9 chromosomes and an estimated genome size of 714-758 Mbp. The taxonomical position of the species is within the Amaranthaceae family and in the order Caryophyllales. The plant is an important crop in Europe and the US, accounting for 30% of the yearly global sugar production. While beet varieties cultivated for their leaves have been known since Roman times, sugar beet is one of the most recently domesticated crops. First efforts of breeding sugar beets date back to the end of the 18^th century, following the discovery that the sugar accumulating within the beet’s storage root is chemically identical to sugar extracted from sugar cane.
We sequenced the sugar beet genome and generated an assembly that encompasses 567 Mbp, of which 85% are chromosomally assigned. This genome sequence is the first representative from the Caryophyllales clade, a taxon comprising 11,500 species. In addition to Beta vulgaris and Spinacia oleracea, this clade also includes species such as the cacti, stone plants, and several carnivorous taxa. It has been shown previously that beets share an ancient genome triplication with other eudicot plants. We now constructed phylogenetic trees for each sugar beet gene (collectively referred to as “phylome”) and used the data to infer accurate phlyogenies among eudicot plants. Our analysis revealed the separation of Caryophyllales prior to the split of rosids and asterids. The genome contains about 27,500 protein-coding genes that were predicted with the support of transcript data. Sugar beet contains less genes encoding transcription factors than any other taxon included in our analysis (five rosids, two asterids, two monocots).
The sugar beet genome sequence paves the way for further molecular and comparative studies in sugar beet, Caryophyllales and eudicot plants.