Is partial desynapsis in cauliflower (Brassica oleracea L. var. botrytis) pollen mother cells linked to aneuploidy in the crop?

Trisomic cauliflower plants (Brassica oleracea L. var. botrytis) display abnormal curd phenotypes that seriously decrease commercial value of the crop. Despite extensive breeding efforts, selection of genotypes producing euploid gametes remains unsuccessful due to unknown genetic and environmental factors. To reveal an eventual role of an-euploid gametes, we analyzed chromosome pairing, chiasma formation and chromosome segregation in pollen mother cells of selected cauliflower genotypes. To this end we compared three genotypes exhibiting Low with < 5%, Moderate with 5-10% and High with > 10% aberrant offspring, respectively. Although chromosome pairing at pachytene was regular, cells at diakinesis and metaphase I showed variable numbers of univalents, suggesting partial desynapsis. Cells at anaphase I-telophase II exhibit various degrees of unbalanced chromosome numbers, that may explain the aneuploid offspring. Immunofluorescence probed with an MLH1 antibody demonstrated fluorescent foci in all genotypes, but their lower numbers do not correspond to the number of putative 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 chromatin connections seem 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 does show interchromosomal connections, but there are no indications for partial desynapsis. The causality of the curd development on the desynapsis in cauliflower is still a matter of debate.