Isolation and characterization of five rice telomere-associated sequences

Construction of rice mini-chromosomes by telomere-mediated chromosomal truncation

Telomere truncation has been shown to be an efficient technology for the creation of mini-chromosomes that can be used as artificial chromosome platforms for genetic engineering. Artificial chromosome-based genetic engineering is considered to be superior to the existing techniques of randomized gene integration by Agrobacterium or biolistic-mediated genetic transformation. It organizes multiple transgenes as a unique genetic linkage block for subsequent manipulations in breeding. Telomere truncation technology relies on three components: the telomere sequence that mediates chromosomal truncation, a selection marker that allows the selection of transgenic events, and a site-specific recombination system that can be used to accept future genes into the mini-chromosome by gene targeting. These elements are usually pre-assembled before transformation, a process that is both time and labor consuming. We found in this research that the three elements could be mixed to transform plant cells in a biolistic transformation, and produced efficient chromosomal truncations and mini-chromosomes in rice. This system will allow rapid construction of mini-chromosomes with a flexible selection of resistant markers, site-specific recombination systems and other desirable elements. In addition, a rice telotrisomic line was used as the starting material for chromosomal truncations. Mini-chromosomes from the truncations of both the telocentric chromosome and other chromosomes were recovered. The mini-chromosomes remained stable during 2 years of subculture. The construction of mini-chromosomes in rice, an economically important crop, will provide a platform for future artificial chromosome-based genetic engineering of rice for stacking multiple genes.

The centromeric regions of potato chromosomes contain megabase-sized tandem arrays of telomere-similar sequence

Telomere-similar sequences have been found in non-telomeric regions in various eukaryotic species. Centromeric regions often harbor such interstitial telomeric repeats (ITRs). We isolated a 2.8 kb ITR, pSbTC1, in a diploid potato species Solanum bulbocastanum. DNA sequences related to the pSbTC1 family are widely distributed in different Solanum species. The pSbTC1-related sequences are organized into tandem arrays and located mainly in the centromeric regions of potato chromosomes. Most notably, the pSbTC1-related sequences have undergone extensive amplification and a single array can span up to multiple megabases. These results suggest that the pSbTC1-related sequences are not simple relics of ancient events in karyotype evolution, such as chromosomal fusions. We also demonstrated that the pSbTC1-related sequences are heavily methylated and are associated with highly condensed centromeric heterochromatin.