Centromere Size and Its Relationship to Haploid Formation in Plants

• Published in: Molecular plant 2018-03, Vol.11 (3), p.398-406
• Main Authors: Wang, Na, Dawe, R. Kelly
• Format: Article
• Language: English
• Subjects: aneuploidy; CENH3; CENP-A; Centromere - genetics; Centromere - metabolism; chromosome loss; genome elimination; Genome, Plant - genetics; Haploidy; kinetochore; Kinetochores - metabolism; Plant Proteins - genetics; Plant Proteins - metabolism
• ISSN: 1674-2052; 1752-9867
• DOI: 10.1016/j.molp.2017.12.009

Wide species crosses often result in uniparental genome elimination and visible failures in centromere function. Crosses involving lines with mutated forms of the CENH3 histone variant that organizes the centromere/kinetochore interface have been shown to have similar effects, inducing haploids at high frequencies. Here, we propose a simple centromere size model that endeavors to explain both observations. It is based on the idea of a quantitative centromere architecture where each centromere in an individual is the same size, and the average size is dictated by a natural equilibrium between bound and unbound CENH3 (and its chaperones or binding proteins). While centromere size is determined by the cellular milieu, centromere positions are heritable and defined by the interactions of a small set of proteins that bind to both DNA and CENH3. Lines with defective or mutated CENH3 have a lower loading capacity and support smaller centromeres. In cases where a line with small or defective centromeres is crossed to a line with larger or normal centromeres, the smaller/defective centromeres are selectively degraded or not maintained, resulting in chromosome loss from the small-centromere parent. The model is testable and generalizable, and helps to explain the counterintuitive observation that inducer lines do not induce haploids when crossed to themselves. Centromere size, defined as the space occupied by Centromeric Histone H3 (CENH3) on a chromosome, varies among species. Wide crosses involving large- and small-centromere species often results in loss of the small-centromere genome. We compare this with the case of CENH3-mediated haploid formation, where plants with altered CENH3 induce haploids, and propose a simple model to explain both observations.