Recovery of a telomere-truncated chromosome via a compensating translocation in maize

Abstract

Maize-engineered minichromosomes are easily recovered from telomere-truncated B chromosomes but are rarely recovered from A chromosomes. B chromosomes lack known genes, and their truncation products are tolerated and transmitted during meiosis. In contrast, deficiency gametes resulting from truncated A chromosomes prevent their transmission. We report here a de novo compensating translocation that permitted recovery of a large truncation of chromosome 1 in maize. The truncation (trunc-1) and translocation with chromosome 6 (super-6) occurred during telomere-mediated truncation experiments and were characterized using single-gene fluorescent in situ hybridization (FISH) probes. The truncation contained a transgene signal near the end of the broken chromosome and transmitted together with the compensating translocation as a heterozygote to approximately 41%-55% of progeny. Transmission as an addition chromosome occurred in ~15% of progeny. Neither chromosome transmitted through pollen. Transgene expression (Bar) cosegregated with trunc-1 transcriptionally and phenotypically. Meiosis in T1 plants revealed eight bivalents and one tetravalent chain composed of chromosome 1, trunc-1, chromosome 6, and super-6 in diplotene and diakinesis. Our data suggest that de novo compensating translocations allow recovery of truncated A chromosomes by compensating deficiency in female gametes and by affecting chromosome pairing and segregation. The truncated chromosome can be maintained as an extra chromosome or together with the super-6 as a heterozygote.

Induction of telomere‐mediated chromosomal truncation and stability of truncated chromosomes in Arabidopsis thaliana

“…Similar observations were made for other A. thaliana minichromosomes (Murata et al, 2008). In contrast, engineered minichromosomes derived from the maize standard A chromosome complement failed to transmit through meiosis in most cases due to deficiency gametes (Yu et al, 2006(Yu et al, , 2007Gaeta et al, 2011). Thus, it is likely that the transmission of minichromosomes is affected by their size reduction and by specific properties of the host species.…”

“…In contrast, engineered minichromosomes derived from the maize standard A chromosome complement failed to transmit through meiosis in most cases due to deficiency gametes (Yu et al. , 2006, 2007; Gaeta et al. , 2011).…”

Telomere-mediated truncation of barley chromosomes

“…Disfavoured transmission of truncated chromosomes was also noted for telomeremediated truncated chromosomes of tetraploid A. thaliana, where transmission rates of truncated chromosomes were in the range of 50% to 65% (Teo et al 2011). In contrast, truncated chromosomes derived from the maize standard A chromosome complement failed to transmit through meiosis in most cases (Gaeta et al 2011;Yu et al 2006Yu et al , 2007. Thus, the transmission of truncated chromosomes seems to be impaired.…”

Induction of telomere‐mediated chromosomal truncation and behavior of truncated chromosomes in Brassica napus

“…Disfavored transfer of truncated chromosomes was also observed in tetraploid A. thaliana , in which transmission rates of truncated minichromosomes ranged from 50% to 65% (Teo et al ., ). Telomere‐mediated truncated chromosomes failed to transfer over generations in most cases for the A chromosomes in maize (Yu et al ., , ; Gaeta et al ., ). In this study, the telomere‐induced truncated chromosome was transferred through meiosis in B. napus at a rate of 31% instead of the expected 75% among the progeny of selfed F 1 plants.…”