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Abstract

Meiotic chiasmata were analysed in metaphase I pollen mother cells (PMCs) of wild-type Arabidopsis thaliana and in two meiotic mutants. Fluorescence in situ hybridisation (FISH) with 45S rDNA and 5S rDNA as probes was used to identify the five chromosome pairs. A wild-type chiasma frequency of 9.24 per cell was found, consistent with estimated genetic recombination values. Individual bivalent chiasma frequencies varied according to chromosome size; chromosome 1 had the highest mean chiasma frequency (2.14) while the short acrocentric chromosomes had the lowest frequencies (1.54 and 1.56). FISH analysis was extended to two meiotic mutants (asy1 and dsy1) having low residual bivalent and chiasma frequencies. Mutant dsy1 gave no indication of chromosome preference for residual bivalent formation; instead it showed a general reduction in bivalent and chiasma frequencies. In asy1, the longest chromosome (1) had the lowest bivalent frequency and chiasma frequency while the short acrocentric chromosome 2 had the highest frequencies. This chromosome pair may be preferentially involved in synapsis and chiasma formation because of their association with the nucleolus. However, other factors may be operating since the other acrocentric chromosome (4), with similar size and structure to chromosome 2, did not share these chiasma properties.

The condensin complexes play distinct roles to ensure normal chromosome morphogenesis during meiotic division in Arabidopsis

“…The chiasma frequency was scored at metaphase I in chromosome-spread preparations labelled using fluorescence in situ hybridization (FISH) with 45S and 5S ribosomal (rDNA) to distinguish the individual chromosomes (Sanchez-Moran et al ., 2001). A slight reduction in the mean chiasma frequency for both lines was detected, from 9.05 chiasma per cell for the wild-type ( n = 20) to 8.44 in AtSMC4 RNAi-1 ( P = 0.0531, n = 32) and 8.15 in AtSMC4 RNAi-2 ( P = 0.007, n = 25).…”

“…To investigate the integrity of the rDNA during meiosis in the AtSMC4 RNAi lines, FISH analysis was conducted using the 45S and 5S rDNA probes Sanchez-Moran et al ., 2001). There were no obvious differences between the wild type and AtSMC4 RNAi at prophase I, but at metaphase I the signals appeared enlarged in AtSMC4 RNAi (Figure6a–d).…”

Zip4/Spo22 Is Required for Class I CO Formation but Not for Synapsis Completion in Arabidopsis thaliana

“…First, the overall level of meiotic recombination was estimated by measuring the mean number of chiasmata at metaphase I on spread PMC chromosomes, as described in [26]. The Atzip4 alleles are in two different ecotypes (Ws for Atzip4-1 and Atzip4-3 and Col-0 for Atzip4-2 ), and because this measurement is known to vary among genotypes [27], we compared chiasma frequency in all Atzip4 mutants to their respective wild type.…”

On the role of some ARGONAUTE proteins in meiosis and DNA repair in Arabidopsis thaliana

“…On the other hand, condensation represents an advantage when FISH is applied. The chromosomes of Arabidopsis can be individually distinguished for the purpose of chiasma counting following FISH with probes for 45S and 5S rDNA (Sánchez-Morán et al, 2001, 2002; López et al, 2012). …”

“…Fixation of flower buds, slide preparations of PMCs, and fluorescence in situ hybridization (FISH) were carried out according to Sánchez-Morán et al (2001). The DNA probes used comprise ribosomal DNA 5S and 45S loci to identify individual bivalents (Gerlach and Bedbrook, 1979; Campell et al, 1992), and a 180 bp repeat sequence (pAL1) to detect centromeres (Martínez-Zapater et al, 1986).…”