The B chromosome of maize: Drive and Genomic Conflict

University Of Missouri-Columbia, Columbia MO

Investigators

Abstract

Varieties of corn have an extra chromosome that is not essential called the B chromosome. This chromosome has properties that, based on analysis of its DNA sequence, have allowed it to persist from one generation to the next for millions of years, despite the fact that it is not needed for the plant. While these properties are beneficial to the success of the B chromosome, they often have negative consequences for the normal corn chromosomes such as chromosome fracture and the activation of transposable elements that have the potential to jump around the genome and cause mutations. A genetic and molecular analysis will be conducted to learn the nature of these B chromosome properties and how the corn genome has been impacted by the presence of the B chromosome. The B chromosome appears to have been involved in restructuring the corn chromosomes, so an understanding of these properties will help provide insight into the nature of, and variation in the maize genome. The research will involve participants at all educational levels and will involve training in genetics, genomics, and computational biology. The supernumerary B chromosome of maize is a novel, selfish genetic system involving a whole chromosome that impacts genomic processes in general. The B chromosome has manipulated cellular processes to ensure proper segregation in male meiosis by increasing recombination in heterochromatin, by using a novel meiotic process to stabilize itself in meiosis, by delaying replication of the centromere at the one mitosis that makes the two sperm, and by mediating fertilization of the egg by B containing sperm. Experiments will examine the mechanism of centromere nondisjunction, the identity and function of the trans-acting factors needed for nondisjunction, the nature of the univalent stabilization process, the nature of the modulation of recombination across the genome, and aspects of genomic conflict such as de-silencing of transposable elements, identifying the gene responsible for genomic shattering by B chromosomes in some backgrounds, and the gene responsible for variation in preferential fertilization. The completion of this project will provide data that support a new paradigm in the understanding of a suite of co-opted functions by a mega selfish genetic entity. The interdisciplinary team will seek to understand this selfish entity to gain new insight into concepts previously unexplored in any system about genetic drive and genomic conflict. A training program across biological disciplines with computational analyses will be conducted at all educational levels. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.