Misdivision analysis of centromere structure in maize.

Abstract

The size and organization of a representative plant centromere from the supernumerary B chromosome were determined using a repeated sequence specific to the centric region. Several derivatives of the B chromosome that suffered from misdivision of the centromere were analyzed for the content and organization of their B repeat. In all these derivatives, major rearrangements were detected. Some misdivisions produced a significant reduction in size of the B‐specific cluster. These results demonstrate that the B repeat is part of the functional centromere, that it is spread throughout its length, and that plant centromeres are composed of repeat units that can be significantly changed in copy number without a change in function.

Arabidopsis thaliana Centromere Regions: Genetic Map Positions and Repetitive DNA Structure

“…The A. thaliana centromere regions are rich in repetitive DNAs, which is a hallmark of the molecularly characterized centromere regions from humans (Willard and Wayne 1987), mice (Kipling et al 1991;Narayanswami et al 1992), maize (Alfenito and Birchler 1993;Kaszás and Birchler 1996), Drosophila (Le et al 1995;Murphy and Karpen 1995), Neurospora (Centola and Carbon 1994), and fission yeast (Nakaseko et al 1986;Clarke 1990). A. thaliana centromeres contain long arrays of 180-bp repeats with little or no interspersion, in addition to the more complex arrays of 180-bp repeats mixed with other repeat elements characterized previously (Richards et al 1991;Pelissier et al 1996;Thompson et al 1996a,b).…”

“…The current physical maps of the A. thaliana genome based on overlapping genomic clones do not represent the large 180-bp arrays described here, and we believe that the centromeres are missing from these maps (Schmidt et al 1995;Zachgo et al 1996). It may be necessary to analyze A. thaliana centromeres that have been pared down in subchromosomal derivatives rather than rely on assembly of centromeric regions from constituent genomic clones Brown et al 1994;Le et al 1995;Murphy and Karpen 1995;Kaszás and Birchler 1996).…”

Do These Sequences Make CENs Yet?

“…Analysis of a normal plant centromere from the supernumerary B chromosome of maize (Alfenito and Birchler 1993;Kaszas and Birchler 1996) indicated that this centromere spans ∼9 Mb and is composed of a sequence repeat, highly degenerate in length but that has a plurality unit of 1.4 kb. Part of this repeat shows strong homology to a maize neocentromere unit sequence of 90 bp.…”

“…Analysis of the B chromosome of maize provided a demonstration that the repetitive sequences at plant centromeres are included in the functional kinetochore (Alfenito and Birchler 1993;Kaszas and Birchler 1996). By using successively rearranged chromosomes caused by centromere fission or misdivision, the central portion of the B centromere was displaced to a new location.…”

“…However, the divisibility of centromeres because of their repetitive structure provides hope that attempts to produce predesigned artificial chromosomes will soon be possible. The centromere of the maize B chromosome was divided by successive misdivision from a progenitor size of ∼9 Mb to derivatives with centromeres of only a few hundred kilobases (Kaszas and Birchler 1996). Because the breaks involved to produce these chromosomes were random and a small sample, it is likely that centromeres in the 100-to 200-kb range might function sufficiently well.…”