Sequence exchange between homologous chromosomes through crossing over and gene conversion is highly conserved among eukaryotes, contributing to genome stability and genetic diversity. Lack of recombination limits breeding efforts in crops, therefore increasing recombination rates can reduce linkage-drag and generate new genetic combinations. We use computational analysis of 13 recombinant inbred mapping populations to assess crossover and gene conversion frequency in the hexaploid genome of wheat (Triticum aestivum). We observe that high frequency crossover sites are shared between populations and that closely related parental founders lead to populations with more similar crossover patterns. We demonstrate that gene conversion is more prevalent and covers more of the genome in wheat than in other plants, making it a critical process in the generation of new haplotypes, particularly in centromeric regions where crossovers are rare. We have identified QTL for altered gene conversion and crossover frequency and confirm functionality for a novel RecQ helicase gene that belongs to an ancient clade that is missing in some plant lineages including Arabidopsis. This is the first gene to be demonstrated to be involved in gene conversion in wheat. Harnessing the RecQ helicase has the potential to break linkage-drag utilizing widespread gene conversions.
Main Text:There is an evolutionary requirement for genetic diversity across a species. Shuffling of material between homologous chromosomes, or genetic recombination, breaks linkage between genes resulting in offspring that have combinations of alleles that differ from those found in either of the parents. During meiosis, double-strand breaks (DSBs) can generate sequence variation in gametes via the DSB repair model (Szostak et al., 1983). DSBs are resolved either by homologous recombination as crossovers (COs) i.e. the reciprocal exchange of large regions between chromosomes, or otherwise as non-crossovers (NCOs). A minimum of one CO per chromosome during meiosis is a requirement for proper chromosome segregation (Pardo-Manuel De Villena and Sapienza, 2001). When both COs and NCOs are resolved, they can also give rise to gene conversions (GCs) as a mechanism of DSB repair involving the non-reciprocal transfer of short DNA segments between homologous non-sister chromatids (Sun et al., 2012;Halldorsson et al., 2016). GCs can be