Engineered minichromosomes in plants.

Artificial chromosome platforms are described in plants. Because the function of centromeres is largely epigenetic, attempts to produce artificial chromosomes with plant centromere DNA have failed. The removal of the centromeric sequences from the cell strips off the centromeric histone that is the apparent biochemical marker of centromere activity. Thus, engineered minichromosomes have been produced by telomere mediated chromosomal truncation. The introduction of telomere repeats will cleave the chromosome at the site of insertion and attach the accompanying transgenes in the process. Such truncation events have been documented in maize, Arabidopsis, barley, rice, Brassica and wheat. Truncation of the nonvital supernumerary B chromosome of maize is a favorite target but engineered minichromosomes derived from the normal A chromosomes have also been recovered. Transmission through mitosis of small chromosomes is apparently normal but there is loss during meiosis. Potential solutions to address this issue are discussed. With procedures now well established to produce the foundation for artificial chromosomes in plants, current efforts are directed at building them up to specification using gene stacking methods and editing techniques.