B chromosomes (Bs) are supernumerary chromosomes, which are often preferentially inherited. When transmission rates of chromosomes are higher than 0.5, not obeying the Mendelian law of equal segregation, the resulting transmission advantage is collectively referred to as 'chromosome drive'. Here we analysed the drive mechanism of Aegilops speltoides Bs. The repeat AesTR-183 of A. speltoides Bs, which also can be detected on the Bs of Aegilops mutica and rye, was used to track Bs during pollen development. Nondisjunction of CENH3-positive, tubulin interacting B sister chromatids and an asymmetric spindle during first pollen grain mitosis are key for the accumulation process. A quantitative flow cytometric approach revealed that, independent of the number of Bs present in the mother plant, Bs accumulate in the generative nuclei to > 93%. Nine out of 11 tested (peri)centromeric repeats were shared by A and B chromosomes. Our findings provide new insights into the process of chromosome drive. Quantitative flow cytometry is a useful and reliable method to study the drive frequency of Bs. Nondisjunction and unequal spindle organization accompany during first pollen mitosis the drive of A. speltoides Bs. The prerequisites for the drive process seems to be common in Poaceae.

Biology Centre Czech Academy of Sciences Ceske Budejovice Czech Republic

Department of Plant Biology College of Agronomy 12900 Montevideo Uruguay

Leibniz Institute of Plant Genetics and Crop Plant Research Gatersleben 06466 Seeland Germany

Triticeae Institute Sichuan Agricultural University 611130 Chengdu China

References provided by Crossref.org

The genetic mechanism of B chromosome drive in rye illuminated by chromosome-scale assembly

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MK283665, MK283666, MK283667, MK283668, LS992081.1, KC290900.1