Sterility and structural variation in an arabidopsis pedigree carrying a ring minichromosome

Circular minichromosomes could be useful tools for plant biotechnology, yet their long-term structural stability, heritability, and effects on phenotype remain poorly understood. In this study, we report a multi-generational analysis of the Arabidopsis mini1a ring minichromosome, which originated from the chromosome 1 centromere in a haploid induction cross. Is mini1a unstable, as suggested by classical studies on other ring chromosomes? Using whole-genome sequencing of individuals carrying mini1a representing multiple successive generations, we uncovered a major catastrophe driven by DNA breaks and novel junction formation, resulting in a new version of mini1a, that carries a 1.3 Mb deletion in the centromeric region (mini1aΔ). We identified 20 new breakpoints, of which 7 disrupted gene bodies-a frequency unlikely to occur by chance. Interestingly, both mini1a and mini1aΔ could exist in one or two copies and could co-exist in a single plant. Although they were inherited efficiently, their presence was sometimes associated with plant sectors with 100% sterility. These findings highlight the structural plasticity of mini1a. At the same time, they raise questions regarding the mechanisms underlying the observed reduced plant fertility. In summary, circular minichromosomes can be deleterious and biotechnology applications based on the manipulation of minichromosomes will require careful planning and testing.