Gene

Meiosis

Organic chemistry

Chemistry

Nondisjunction

Aneuploidy

Toxicity

Chromosome

Small supernumerary marker chromosome

Micronucleus test

Karyotype

Anaphase

Genetics

Chromatid

B chromosome

Chromatin

Biology

Mitosis

Cell biology

Nature Communications

Not necessarily all cells of an organism contain the same genome. Some eukaryotes exhibit dramatic differences between cells of different organs, resulting from programmed elimination of chromosomes or their fragments. Here, we present a detailed analysis of programmed B chromosome elimination in plants. Using goatgrass Aegilops speltoides as a model, we demonstrate that the elimination of B chromosomes is a strictly controlled and highly efficient root-specific process. At the onset of embryo differentiation B chromosomes undergo elimination in proto-root cells. Independent of centromere activity, B chromosomes demonstrate nondisjunction of chromatids and lagging in anaphase, leading to micronucleation. Chromatin structure and DNA replication differ between micronuclei and primary nuclei and degradation of micronucleated DNA is the final step of B chromosome elimination. This process might allow root tissues to survive the detrimental expression, or overexpression of B chromosome-located root-specific genes with paralogs located on standard chromosomes.

Supernumerary B chromosomes of Aegilops speltoides undergo precise elimination in roots early in embryo development