Construction and Applications of Engineered Minichromosomes in Plants

Synthetic/artificial chromosome platforms in plants have been produced via telomere-mediated chromosomal truncation. The telomere repeats when introduced during a transformation event cleave the chromosome at the site of introduction. The frequency of such events is sufficiently high that very small chromosomes can be produced that carry an endogenous centromere together with introduced genes and sites that will allow further additions to the minichromosome. This approach bypasses the epigenetic aspects of centromere specification in plants in that centromere sequences are neither necessary nor sufficient for centromere activity. The ability to modify engineered minichromosomes in vivo has been demonstrated. A proof of concept using supernumerary B chromosomes as an example illustrates that this technology could be combined with doubled haploid breeding. By incorporating a minichromosome into a maize haploid inducer line, it should be possible to transfer the minichromosome to maternal haploids at a workable frequency to introduce them into multiple lines or to test the reaction of a transgene in different genetic backgrounds with a bypass of extensive introgression. With the ability to make further additions to the artificial chromosome platform, it should be possible to introduce whole biochemical pathways to plants to confer new properties upon them or to use plants as factories for the large-scale production of useful metabolites or pharmaceuticals. Useful properties that could be combined on a synthetic chromosome include herbicide, insect, fungal, viral and bacterial resistances, drought tolerance, efficient nitrogen utilization, nutritional improvements and favorable quantitative traits to improve yield.