Genomics and Cytogenetics Of Arabidopsis Minichromosomes

Engineered minichromosomes have been proposed as a new generation plant breeding tool to stack and propagate desired agronomic traits in crops of interest.  Here we describe a novel method to produce minichromosomes in Arabidopsis thaliana that may be generally applicable to other plants. We previously showed that genetic crosses featuring parental differences in an essential kinetochore protein (CENH3) can lead to drastic chromosome missegregation. This probably occurs because chromosomes containing hypomorphic CENH3 are outcompeted by wild type chromosomes. We have found that chromosome missegregation leads to chromosome fragmentation and DNA repair during zygotic mitosis, generating a series of minichromosomes in A. thaliana. The minichromosomes thus generated varied in size and were stably transmitted over several generations without any compromise to plant fertility. Accurate segregation of minichromosomes during meiosis is a major concern for their exploitation in crop biotechnology. In order to address this, we examined the meiotic behaviour of unpaired minichromosomes in haploid and diploid A.thaliana plants. Further, we describe the meiotic dynamics of paired minichromosomes. Centromeres in Arabidopsis  are heterochromatic and recombination-suppressed, so it will be interesting to see how large minichromosomes must be to ensure an obligate crossover. Lastly, we describe an easy approach for “horizontal transfer” of minichromosomes across different strains which has great implications for its commercial exploitation.

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