Evidence from a maize desynaptic mutant points to a probable role of synaptonemal complex central region components in provision for subsequent chiasma maintenance

Abstract

Homozygotes for the dsy1 desynaptic mutant of maize show massive failure of chiasma maintenance during diplotene and diakinesis. Although some chiasmata persist until anaphase I in most microsporocytes expressing this mutant, homozygotes are completely or nearly completely sterile, owing apparently to disjunctive irregularities. Pachytene synaptic errors and some synaptic failure also are found, but recombination nodules are common in homologously synapsed regions, and equational separation of a heterozygous knob into univalents or open arms at diakinesis clearly demonstrates that chiasma failure occurs following crossing-over. A wider than normal synaptonemal complex central region and uniform apparent weakness of central region cross connections to spreading procedures strongly suggest the presence of a genetic lesion in a synaptonemal complex central region component. The dsy1 mutant may provide an especially important source of material for molecular studies on the nature of chiasma maintenance mechanism.

Altered Nuclear Distribution of Recombination Protein RAD51 in Maize Mutants Suggests the Involvement of RAD51 in Meiotic Homology Recognition

“…Golubovskaya, unpublished data dsy1-1 High frequency of univalents but bivalents occasionally also present at metaphase I. Axial elements form normally, but synapsis is mostly abnormal: unsynapsed chromosomes, promiscuous synapsis (chromosomes switching pairing partners along their lengths), and intrachromosomal synapsis frequent at pachytene. Golubovskaya and Mashenkov, 1976;Timofeeva and Golubovskaya, 1991;Maguire et al, 1993 dsy9901 Mild defects in chromosome pairing: on average, eight bivalents present at metaphase I. Golubovskaya et al, 2003 dsyCS Severe defects in chromosome pairing: almost exclusively univalents at metaphase I.…”

“…The seven maize meiotic mutants were selected so that they display a range of phenotypes with regard to the severity of their pairing defects. Using information available in the literature (Beadle, 1930;Miller, 1963;Golubovskaya and Mashenkov, 1976;Maguire, 1978aMaguire, , 1978bGolubovskaya and Khristolyubova, 1985;Golubovskaya, 1989;Staiger, 1990;Maguire and Riess, 1991;Timofeeva and Golubovskaya, 1991;Maguire et al, 1993;Golubovskaya et al, 2003), we ordered the mutants relative to each other according to the severity of their phenotypes ( Figure 1). As the main criterion, we used the average number of bivalents at metaphase I (Miller, 1963;Golubovskaya and Mashenkov, 1976;Golubovskaya and Khristolyubova, 1985;.…”

The maize (Zea mays) desynaptic (dy) mutation defines a pathway for meiotic chromosome segregation, linking nuclear morphology, telomere distribution and synapsis

“…The chromosomes in dy appear normal at the pachytene stage of male meiotic prophase, but many of the bivalents separate into univalents by late prophase. In previous studies, the chromosomes at the pachytene stage of prophase I appear fully synapsed at first, but they exhibit extensive precocious desynapsis and chiasma-maintenance failure (Maguire et al, 1991;Maguire et al, 1993). Others have shown dy to affect the control of meiotic recombination (Ji et al, 1999).…”

Isolation and Characterization of SYN1, a RAD21-like Gene Essential for Meiosis in Arabidopsis

“…Based on similarities to meiotic genes identified in other organisms, several genes expressed during meiosis have been identified in Arabidopsis (Sato et al, 1995;Klimyuk and Jones, 1997), lily (Kobayashi et al, 1994), and wheat (Ji and Langridge, 1994). In addition, meiotic mutants have been identified in numerous plants species, including Arabidopsis (Dawson et al, 1993;Chaudhury et al, 1994;He et al, 1996;Peirson et al, 1996;Ross et al, 1997;Spielman et al, 1997;Glover et al, 1998), maize (Golubovskaya et al, 1993(Golubovskaya et al, , 1997Maguire et al, 1993;Staiger and Cande, 1993), rice Omura, 1983, 1984), and tomato (Moens, 1969). The characterization of meiotic mutants and their use in the isolation of the corresponding genes are beginning to provide further insight into the molecular events that accompany meiosis in plants.…”