Association of homologous chromosomes during floral development

Abstract

Reduction in chromosome number and genetic recombination during meiosis require the prior association of homologous chromosomes, and this has been assumed to be a central event in meiosis. Various studies have suggested, however, that while the reduction division of meiosis is a universally conserved process, the pre-meiotic association of homologues differs among organisms. In the fruit fly Drosophila melanogaster, some somatic tissues also show association of homologues [1,2]. In the budding yeast Saccharomyces cerevisiae, there is some evidence for homologue association during the interphase before meiotic division [3,4], and it has been argued that such associations lead directly to meiotic homologue pairing during prophase I [5]. The available evidence for mammals suggests that homologous chromosomes do not associate in germ cells prior to meiotic prophase [6]. To study the occurrence of homologue pairing in wheat, we have used vibratome tissue sections of wheat florets to determine the location of homologous chromosomes, centromeres and telomeres in different cell types of developing anthers. Fluorescence in situ hybridization followed by confocal microscopy demonstrated that homologous chromosomes associate pre-meiotically in meiocytes (germ-line cells). Surprisingly, association of homologues was observed simultaneously in all the surrounding somatic tapetum cells. Homologues failed to associate at equivalent stages in a homologue recognition mutant. These results demonstrate that the factors responsible for the recognition and association of homologues in wheat act before the onset of meiotic prophase. The observation of homologue association in somatic tapetum cells demonstrates that this process and meiotic division are separable.

Higher Levels of Organization in the Interphase Nucleus of Cycling and Differentiated Cells

“…However, this might not be the case in derived differentiated cell types. Aragon-Alcaide et al (6) used GISH with total genomic DNA from barley and observed homologue pairing of two barley chromosomes in premeiotic anther cells of a wheat cultivar carrying a barley substitution. Interestingly, when homologue pairing becomes apparent in the developing meiocytes, the tapetal cells that surround them, which do not themselves undergo meiosis, also show homologous chromosome associations.…”

Examination of Interchromosomal Interactions in Vegetatively Growing DiploidSchizosaccharomyces pombeCells by Cre/loxP Site-Specific Recombination

“…In other higher eukaryotes, somatic pairing is restricted to specific loci/sequences or cell types or suspected from the existence of transsensing effects. In plants, somatic pairing has been detected in the floral tissue of wheat (Aragon-Alcaide et al 1997). In mammals' chromosomal regions, somatic pairing is generally absent, but examples of time-and stage-specific pairing of particular loci have been described (e.g., at centromeres in the cerebellum (Arnoldus et al 1989) and, most recently, as part of X chromosome inactivation in the female (Xu et al 2006).…”

Plant chromosome homology: hypotheses relating rendezvous, recognition and reciprocal exchange

“…Early alignment also was seen for a pair of rye chromosome arms added to wheat (Schwarzacher, 1997). Aragon-Alcaide et al (1997) have shown that, in the presence of the Ph gene (but not in its absence), barley homologous chromosomes (added to wheat) are closely aligned and separated from homeologs in premeiotic G2. Additionally the Ph locus "demands" a high level of homology.…”