An overview of recent advances on wheat homologous and homoeologous recombination.

Crop breeding relies on the creation of high-performance varieties that possess a genotype containing numerous agronomical traits of interest. The specific combination of traits is generated in the parents by meiotic recombination, a highly conserved and controlled cellular process. Improvement of recombination, both in terms of quantity of crossovers and control of their localisation, would enhance the breeding capacities for all crops. This includes allopolyploid wheats, particularly tetraploid durum wheat (Triticum turgidum ssp. durum, AABB genome) and hexaploid bread wheat (Triticum aestivum, AABBDD), two of the most important cultivated species on the planet. As allopolyploid species, recombination in wheat is subjected to two levels of control: (1) recombination between homologous chromosomes that is biologically favoured but has low frequency and uneven distribution; (2) recombination between homoeologous chromosomes that is prevented, although this is the process that allows the introduction of diversity from related species. During the last ten years, a lot of effort has been focused on identifying and studying genes involved in controlling the rate and distribution of homologous and homoeologous recombination in wheat. In this review, we focus on recent results and propose a model for the control of these two processes.