Finding the “M-gene”

Sugarbeet is a prime example of how a single breeding discovery can significantly improve performance. Prior to the discovery of the monogerm mutant by the Ukrainian scientist Viacheslav F. Savitsky in the 1940s, cultivated sugarbeet was multigerm, where two or more seedlings emerge from one seedball and labor-intensive thinning is needed. Nowadays, all economically grown sugarbeet is monogerm hybrid, which can be mechanically planted and harvested, thus requiring far fewer working hours per hectare.

Origins of sugarbeet genetics

For KWS, the monogerm discovery was initially a harsh lesson: Other companies were quicker at adapting the new finding. KWS’ approach at the time, manual splitting of the seed, was far from being as effective as the genetic monogermity.

Since those times, our understanding of sugarbeet genetics has taken huge leaps forward, while KWS has grown to its role as a hub of collaborative sugarbeet research. Britta Schulz, Principal Scientist in Traits & Genomics, remembers when she started her career at KWS 25 years ago: “Those were the early days of genomics. There were few research resources available for sugarbeet, and we needed to start from scratch in setting up the genomic tools.”

Before publishing: Verification of the M-gene

In 2011, the approximate location of the gene had been defined. This meant that collaborators at Bielefeld University, Berndt Weisshaar and Daniela Holtgräwe, were able to identify the candidate gene. This was made possible by the first version of the sugarbeet reference genome with annotated gene models.

But the work was still not finished: To publish such a research finding, the gene needs to be verified. Genome editing is one of the approaches that can be used for gene verification. “At that time, we were reaching out to the breeders to find an open question linked with a visible phenotype, to demonstrate the power of genome editing,” notes Klaus Schmidt, Group Lead in Cell Biology. The M-gene was a perfect match.

“In the case of the M-gene, the difference between multigerm and monogerm genotypes was only one base pair,” explains Natalja Beying, who works as Scientist in Genome Editing with her focus on sugarbeet. “We took the multigerm genotype and produced a so-called knock-out of the gene with the SDN-1 approach.” In SDN-1, small, targeted deletions or insertions are introduced into the genome of a plant. “The knock-out produced a monogerm phenotype, and this was the final proof for the candidate gene,” she concludes.

Genome editing: a powerful research tool

“This was one of the first times that genome editing was applied successfully to validate a gene in sugarbeet,” says Klaus Schmidt. “Now that we have seen that it works, we can apply the same approaches to other genes, where the phenotype is not so visible.”

Gene validation is currently one of the most important ways in which genome editing is used at KWS. The current EU regulatory framework sees all genome editing methods as genetic modification, which effectively hinders its use for product development.

Gene validation is an important tool for breeders, for example in resistance development. Natalja Beying gives an example of another project where they worked together with Britta Schulz, developing Fusarium (soil-borne fungus) resistance: “By knocking out just one gene, we made plants susceptible to Fusarium attack.” With this kind of information, for example, molecular markers for the functional gene can be effectively used to select pathogen-resistant individuals at an early stage of development. “Genome editing is the tool of choice, especially when you want to know the function of a specific gene,” confirms Britta Schulz. |