Nicolas Blavet, Hua Yang, Handong Su, Pavel Solansky, Ryan N. Douglas, Miroslava Karafiátová, Lucie Simková, Jing Zhang, Yalin Liu, Jie Hou, Xiaowen Shi, Chen Chen, Mohamed El-Walid, Morgan E. McCaw, Patrice S. Albert, Zhi Gao, Changzeng Zhao, Gil Ben-Zvi, Lior Glick, Guy Kol, Jinghua Shi, Jan Vrána, Hana Simková, Jonathan C. Lamb, Kathleen Newton, R. Kelly Dawe, Jaroslav Dolezel, Tieming Ji, Kobi Baruch, Jianlin Cheng, Fangpu Han, James A. Birchler, and Jan Bartos.
PNAS
DOI:10.1073/pnas.2104254118
Abstract B chromosomes are enigmatic elements in thousands of plant and animal genomes that persist in populations despite being nonessential. They circumvent the laws of Mendelian inheritance but the molecular mechanisms underlying this behavior remain unknown. Here we present the sequence, annotation, and analysis of the maize B chromosome providing insight into its drive mechanism. The sequence assembly reveals detailed locations of the elements involved with the cis and trans functions of its drive mechanism, consisting of nondisjunction at the second pollen mitosis and preferential fertilization of the egg by the B-containing sperm. We identified 758 protein-coding genes in 125.9 Mb of B chromosome sequence, of which at least 88 are expressed. Our results demonstrate that transposable elements in the B chromosome are shared with the standard A chromosome set but multiple lines of evidence fail to detect a syntenic genic region in the A chromosomes, suggesting a distant origin. The current gene content is a result of continuous transfer from the A chromosomal complement over an extended evolutionary time with subsequent degradation but with selection for maintenance of this nonvital chromosome. |
