Diversity and determinants of recombination landscapes in flowering plants

Abstract

During meiosis, crossover rates are not randomly distributed along the chromosome and therefore they locally influence the creation of novel genotypes and the efficacy of selection. To date, the broad diversity of recombination landscapes among plants has rarely been investigated, undermining the overall understanding of the constraints driving the evolution of crossover frequency and distribution. The determinants that shape the local crossover rate and the diversity of the resulting landscapes among species and chromosomes still need to be assessed in a formal comparative genomic approach. We gathered genetic maps and genomes for 57 flowering plant species, corresponding to 665 chromosomes, for which we estimated large-scale recombination landscapes. Chromosome length drives the basal recombination rate for each species, but within species we were intrigued to notice that the chromosome-wide recombination rate is proportional to the relative size of the chromosome. Moreover, for larger chromosomes, crossovers tend to accumulate at the ends of the chromosome leaving the central regions as recombination-free regions. Based on identified crossover patterns and testable predictions, we proposed a conceptual model explaining the broad-scale distribution of crossovers where both telomeres and centromeres are important. Finally, we qualitatively identified two recurrent crossover patterns among species and highlighted that these patterns globally correspond to the underlying gene distribution. In addition to the positive correlation between recombination and gene density, we argue that crossover patterns are essential for the efficiency of chromosomal genetic shuffling, even though the ultimate evolutionary potential forged by the diversity of recombination landscapes remains an open question.