Beyond FANCM, What Limits Meiotic Crossover?

Meiotic crossovers generate genetic diversity by creating new allelic combinations. Intriguingly the meiotic crossover rates are restricted within a very narrow range. A minimum of one crossover is formed per pair of homologous chromosomes per meiosis. This "obligate" crossover ensures correct segregation of the homologs at the first division leading to balanced gametes and ultimately favors fertility of an organism.

A great deal has been discovered about how meiotic crossovers are formed. However, very little is known about what limits their formation despite an abundance of molecular precursors. Crossover frequency does not typically vary above of the range of one to four crossovers per homologous pair. Using a forward genetic screen that identifies mutants with increased meiotic crossover frequency, we revealed that Fanconi Anemia Complementation Group M (FANCM) limits meiotic crossover formation in Arabidopsis thaliana by suppressing a normally minor pathway (1). Fanconi anemia is prevented in humans by at least fifteen proteins involved in DNA repair, however many of them do not appear to be conserved in Arabidopsis. Hence, we are now using forward and reverse genetic approaches that are deciphering the link between the components of this DNA repair pathway and meiotic crossover suppression.

Notably, breeding programs are limited by meiotic recombination rates that FANCM and related machinery keep restrictively low. Understanding that FANCM limits meiotic crossover formation may assist in creating new elite lines suited to the world's needs.

1. Crismani et al. (2012). FANCM Limits Meiotic Crossovers. Science, 336(6088), 1588–1590.