Non-homologous chromosome pairing during meiosis in haploid Brassica rapa

Key message Cytological observations of chromosome pairing showed that evolutionarily genome duplication might reshape non-homologous pairing during meiosis in haploid B. rapa. A vast number of flowering plants have evolutionarily undergone whole genome duplication (WGD) event. Typically, Brassica rapa is currently considered as an evolutionary mesohexaploid, which has more complicated genomic constitution among flowering plants. In this study, we demonstrated chromosome behaviors in haploid B. rapa to understand how meiosis proceeds in presence of a single homolog. The findings showed that a diploid-like chromosome pairing was generally adapted during meiosis in haploid B. rapa. Non-homologous chromosomes in haploid cells paired at a high-frequency at metaphase I, over 50% of examined meiocytes showed at least three pairs of bivalents then equally segregated at anaphase I during meiosis. The fluorescence immunostaining showed that the cytoskeletal configurations were mostly well-organized during meiosis. Moreover, the expressed genes identified at meiosis in floral development was rather similar between haploid and diploid B. rapa, especially the expression of known hallmark genes pivotal to chromosome synapsis and homologous recombination were mostly in haploid B. rapa. Whole-genome duplication evolutionarily homology of genomic segments might be an important reason for this phenomenon, which would reshape the first division course of meiosis and influence pollen development in plants.

Automated summary

The cytological observations suggest that evolutionary genome duplication may impact non-homologous chromosome pairing in haploid B. rapa during meiosis. The study demonstrates diploid-like chromosome pairing behavior and well-organized cytoskeletal configurations in haploid B. rapa, indicating a similarity in gene expression patterns related to chromosome synapsis and homologous recombination between haploid and diploid plants. This phenomenon may be attributed to the evolutionary homology of genomic segments resulting from whole-genome duplication, which could reshape the meiosis division course and affect pollen development in plants.