The centromere structure in Robertsonian wheat-rye translocation chromosomes indicates that centric breakage-fusion can occur at different positions within the primary constriction

Abstract

Univalent chromosomes at meiotic metaphase I have a tendency to misdivide at the centromeres. Fusion of the misdivision products may produce Robertsonian translocations. The fine structure of the centromeres in Robertsonian wheat-rye translocation chromosomes was analyzed by fluorescence in situ hybridization (FISH) using two centromere-specific DNA clones: pRCS1, derived from rice, and pAWRC1, derived from rye. Clone pRCS1 hybridizes to the centromeres of all grasses including wheat and rye, whereas clone pAWRC1 is rye specific and hybridizes only to the centromeres of rye. Four of the six wheat-rye translocations derived from a single centric misdivision event (1st generation translocations) had hybrid centromeres, with approximately half of the centromere derived from rye and half from wheat. In the two other 1st generation translocations, the entire centromere was derived from rye. Among eight reconstructed wheat and rye chromosomes that originated from two consecutive centric misdivision-fusion events (2nd generation translocations), T1BS.1BL (derived from T1BS.1RL and T1RS.1BL) and one of three T2BS.2BL (derived from T2RS.2BL and T2BS.2RL) had hybrid centromeres. T1RS.1RL (derived from T1BS.1RL and T1RS.1BL), two of three T2BS.2BL, and all three T2RS.2RL (derived from T2RS.2BL and T2BS.2RL) had rye centromeres. All three 3rd generation translocations had hybrid centromeres with approximately half of the centromere derived from rye. There were no indications that the composite structure of the centromere in these chromosomes affected their behavior in mitosis or meiosis. These observations support the notion of a compound structure of the centromere in higher organisms, and indicate that during the centric breakage-fusion event, centromere breakage may occur in different positions along the segment of the chromosome that interacts with the spindle fibers. Normal behavior of the 1st, 2nd, and 3rd generation centric translocations in mitosis and meiosis indicates that, at least in wheat and rye, centromeres are not chromosome specific.

A Molecular-Cytogenetic Method for Locating Genes to Pericentromeric Regions Facilitates a Genomewide Comparison of Synteny Between the Centromeric Regions of Wheat and Rice

“…The Dt stocks of wheat and those of other Triticeae species often arise from breaks in the centromere (Sears and Steinitz-Sears 1978;Zhang et al 2001). Briefly, if an RFLP fragment is assigned to a specific chromosome but is not missing in either of the telosomic stocks for that chromosome then it is assigned to the centromeric region ( Figure 1a).…”

Classical and Molecular Cytogenetic Tools to Resolve the Bixa Karyotypes

“…This result suggests that the Robertsonian translocation between 2 smaller chromosomes may have occurred during the evolution of Bixa. Robertsonian interchange is characterized by centromeric fusion (Jones 1998, Zhang et al 2001, Oakey and Beechey 2002, Switonski et al 2003 between 2 acrocentric (Gupta and Gupta 1991) or telocentric (Zhang et al 2001) non-homologous chromosomes, resulting in one metacentric chromosome (Gupta and Gupta 1991, Jones 1998, Zhang et al 2001, Oakey and Beechey 2002. Considering that many species present the SC in the distal portion of the short arm (Leitch and HeslopHarrison 1992, Hanson et al 1996, Liu et al 1997) and the morphometric data of the chromosome 1, a break involving the long arm of 1 chromosome and the short arm of the other probably led to the formation of the metacentric chromosome 1 with the SC adjacent to the centromere, during the genomic evolution of these species.…”

Functional Rice Centromeres Are Marked by a Satellite Repeat and a Centromere-Specific Retrotransposon

“…Mapping the break points of centromere misdivisions is an important approach in defining the functional centromeres Birchler, 1996, 1998;Zhang et al, 2001). We have developed numerous rice telotrisomic stocks, which contain 24 normal chromosomes and one telocentric chromosome, in Zhongxian 3037 (Cheng et al, 2001c).…”