For a resilient plant production system, durable resistances to pests and diseases, and tolerances to abiotic stresses are critical. Wild crop relatives have been selected for millions of years for resilience. Therefore, plant breeders use these genetic sources. When resistances and tolerances are being introgressed, many undesired traits, so-called linkage drag, come along. For removal of these undesired traits, recombination (crossover) is needed between the resistance gene and the linkage drag. During the meiosis only 0 to ~2 crossovers occur per chromosome. The chance for a crossover neighbouring a resistance gene for removal of the linkage drag, is very small. Moreover, breeders cannot influence the positions of the crossovers.
Therefore, breeders make large populations, hoping for a lucky shot. It would accelerate breeding significantly, if the breeder could control the positions of the crossovers. For this aim we apply CRISPR-Cas. This is a very innovative approach, allowing controlled recombination, and a more efficient breeding for resilient crops.
This approach is also very interesting if resistance genes are clustered, but present in different wild donors. For combining these genes on the same chromosome, preventing segregation during breeding, a crossover is required between these genes in the cluster. This is hardly possible in conventional breeding, but the approach proposed here should make it feasible.
During evolution numerous chromosomal rearrangements have occurred, including inversions. Sometimes, resistance/tolerance genes reside in such inversions. Homologous chromosomes do not show crossovers in inversions. If a resistance gene is located in an inversion, it in unbreakably linked to linkage drag in that inversion. This problem has been known for decades, but has never been solved. This very innovative method expands the possibilities for breeding for resilient, high quality crops.
During the meiosis, the protein SPO11 makes double strand breaks (DSBs) in the DNA for initiation of a crossover. From a scientific perspective, this project will show if it is possible to replace SPO11 by CRISPR-Cas. Moreover, it will show if cold spots of recombination are caused by absence of breaks by SPO11 in these regions, or because of other reasons. Also it will show if these cold spots can become hot spots if CRISPR-Cas replaces SPO11, making only one DSB per chromosome, and therefore only allowing crossovers in that region, and not at other places of the chromosome.