B chromosome and its non-Mendelian inheritance in Atractylodes lancea

Supernumerary B chromosomes contribute to intraspecific karyotypic variation. B chromosomes have been detected in more than 2000 organisms; they possess unique and diverse features, including non-Mendelian inheritance. Here, we report one or more B chromosomes in the gynodioecious plant Atractylodes lancea. Among 54 A. lancea lines, 0-2 B chromosomes were detected in both hermaphroditic and female plants, with the B chromosomes appearing as DAPI-bright regions within the nuclei. Genomic in situ hybridization revealed that the B chromosomes had no conserved A chromosome DNA sequences, confirmed by fluorescence in situ hybridization probed with independently dissected B chromosomes. In male meiosis, the B chromosome did not pair with an A chromosome and was therefore eliminated; accordingly, only 20.1% and 18.6% of these univalent B chromosomes remained at the end of meiosis for the 1B lines of KY17-148 and KY17-118, respectively. However, we also found that B chromosomes were transmitted from male parents in 40.8%-44.2% and 47.2% of the next generation; although these transmission rates from male parents were not essentially different from Mendelian inheritance (0.5), the transmission of gametes carrying B chromosomes increased through fertilization or seed development. B chromosomes were transmitted from three of four 1B female parents to 64.3%-92.6% of the next generation, suggesting B chromosome accumulation. We propose that the B chromosome of A. lancea has a specific sequence and persists via non-Mendelian inheritance from female parents. Overall, A. lancea, with its unique characteristics, is a promising model for understanding the structure, evolution, and mechanism of non-Mendelian inheritance of B chromosomes.