Diversity and Determinants of Meiotic Recombination Landscapes.

Despite the universal importance of meiotic recombination for generating genetic diversity, numbers and distribution of recombination events along chromosomes vary among species, genotypes within species, and between sexes. Some interspecies differences stem from the diversity of genome size and composition among eukaryotes. Large-genome species, such as humans and most crops, display recombination landscapes that are different from those of small-genome yeasts. Chromatin patterns, including histone modifications and DNA methylation, are also responsible for interspecies differences as well as differences between the sexes. Finally, despite the overall recombination pathway conservation, there are species-specific components that result in distinct recombination patterns. Consequently, characteristics that are defining for the recombination landscape and universally shared by all eukaryotes remain largely to be discovered.

Chromosome segregation in plant meiosis.

Faithful chromosome segregation in meiosis is essential for ploidy stability over sexual life cycles. In plants, defective chromosome segregation caused by gene mutations or other factors leads to the formation of unbalanced or unreduced gametes creating aneuploid or polyploid progeny, respectively. Accurate segregation requires the coordinated execution of conserved processes occurring throughout the two meiotic cell divisions. Synapsis and recombination ensure the establishment of chiasmata that hold homologous chromosomes together allowing their correct segregation in the first meiotic division, which is also tightly regulated by cell-cycle dependent release of cohesin and monopolar attachment of sister kinetochores to microtubules. In meiosis II, bi-orientation of sister kinetochores and proper spindle orientation correctly segregate chromosomes in four haploid cells. Checkpoint mechanisms acting at kinetochores control the accuracy of kinetochore-microtubule attachment, thus ensuring the completion of segregation. Here we review the current knowledge on the processes taking place during chromosome segregation in plant meiosis, focusing on the characterization of the molecular factors involved.