Arabidopsis Epichrom
The diploid genome of the model plant Arabidopsis thaliana consists of 10 chromosomes. By inducing CRISPR/Cas-induced breaks at chromosome-specific subcentromeric and subtelomeric sequences, we were able to fuse entire chromosome arms with other chromosomes, obtaining a chromosome number reduction in the process. In the first step, telocentric chromosomes were obtained and in the second step, the remaining arms were relocated. As the remaining centromeric minichromosomes were lost from the progeny, we were able to obtain two genetically distinct 8-chromosome-lines that both lack wild type chromosome 3. In the first line, both arms of chromosome 3 were fused to chromosome 1. In the other line, one arm was transferred to chromosomes 1 and the other to chromosome 5. Both chromosome number-reduced lines are fully fertile, and phenotyping demonstrates no growth retardation in comparison to wild type plants. The progeny of crosses of the 8-chromosome lines with the wild type genotype shows reduced fertility. Interestingly, the meiotic recombination patterns of the transferred chromosome arms drastically changed in comparison to 10-chromosome lines. Thus, the directed change of chromosome numbers in plants will enable new breeding strategies as linkage groups can be redefined and genetic barriers newly established. Moreover, our data indicate that plants are highly robust to engineered karyotype changes, proving a central mechanism of plant genome evolution.