Meiotic Aberrations Leading To Aneuploidy In Cauliflower (Brassica Oleracea L. var. Botrytis)

Abstract

Aneuploid cauliflower plants (Brassica oleracea L. var. botrytis) display abnormal curd phenotypes causing serious commercial problems in offspring populations. Despite extensive breeding efforts, selection of genotypes producing euploid gametes remains unsuccessful due to unknown genetic and environmental factors. To reveal the origin of aneuploid gametes, we analyzed chromosome pairing, chiasma formation and chromosome segregation in pollen mother cells of selected cauliflower genotypes. To this end we compared different genotypes exhibiting Low with < 5%, Moderate with 5-10% and High with > 10% aberrant offspring. Microscopic observations revealed regular chromosome pairing at pachytene. However, cells at diakinesis and metaphase I showed variable numbers of univalents, suggesting that chiasma formation during meiotic prophase is incomplete or disrupted and results in a partial desynaptic phenotype. Cells at anaphase I – telophase II exhibited various degrees of unbalanced chromosome numbers explaining the aneuploid offspring. Immunofluorescence probed with an MLH1 antibody demonstrated fluorescent foci in all genotypes, but their lower numbers do not correspond to the putative sites of chiasmata. Interchromosomal connections between chromosomes and bivalents are common at diakinesis and metaphase I, and they contain centromeric and 45S rDNA tandem repeats, but such threads seemed not to affect proper disjoin of the half bivalents at anaphase I. Moreover, male meiosis in the arabidopsis APETALA1/ CAULIFLOWER double mutant with the typical cauliflower phenotype did show interchromosomal connections, but there were no indications for partial desynapsis. We now hypothesize that the occurrence of desynapsis in cauliflower is a developmental out-of-phase phenomenon partially or completely controlled by genes involved in flower and curd development.

Epigenomic and structural events preclude recombination in Brassica napus

“…Using oligo‐FISH on pachytene chromosomes, we did not detect an inversion loop in the heterozygous hybrid DChEM (for the A10 inversion), and only 3.8% of the analyzed cells presented an absence of coalignment. Similar results were described in Arabidopsis (Ji, 2014; Fransz et al ., 2016), where no synapsis was observed despite a linear coalignment of the inverted region. In this study, the genome alignment of the parental lines of the DChEM F 1 hybrid allowed us to identify a total of three pericentric (1.7–5.6 Mb) and nine paracentric (1.0–2.7 Mb) inversions, for which six paracentric nonpericentromeric regions were analyzed.…”