title: 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.
authors.affiliation: Department of Biological Sciences, University of Missouri-Columbia, Columbia, MO 65211, USA.
authors.forename: Robert T
authors.initials: RT
authors.lastname: Gaeta
authors.forename: Tatiana V
authors.initials: TV
authors.lastname: Danilova
authors.forename: Changzeng
authors.initials: C
authors.lastname: Zhao
authors.forename: Rick E
authors.initials: RE
authors.lastname: Masonbrink
authors.forename: Morgan E
authors.initials: ME
authors.lastname: McCaw
authors.forename: James A
authors.initials: JA
authors.lastname: Birchler
mesh_terms: D015139:Blotting, Southern; D032461:Chromosomes, Plant / Q000235:genetics*; D020869:Gene Expression Profiling; D005818:Genetic Engineering / Q000379:methods*; D017404:In Situ Hybridization, Fluorescence; D040582:Inheritance Patterns / Q000235:genetics; D007621:Karyotyping; D011058:Pollen / Q000235:genetics; D016615:Telomere / Q000235:genetics*; D019076:Transgenes / Q000235:genetics; D014178:Translocation, Genetic / Q000235:genetics*; D003313:Zea mays / Q000235:genetics*