The Arabidopsis thaliana DSB formation (AtDFO) gene is required for meiotic double-strand break formation.

DNA double-strand break (DSB) formation is the initial event for meiotic recombination catalyzed by the conserved Spo11 protein. In Arabidopsis, several proteins have been reported to be involved in DSB formation. Here, we report an Arabidopsis DSB forming (DFO) gene in Arabidopsis that is involved in DSB formation. The dfo mutant exhibits reduced fertility, producing polyads with an abnormal number of microspores, unlike the tetrads in the wild type. The dfo meiocytes were defective in homologous chromosome synapsis and segregation. Genetic analysis revealed that the homologous recombination of Atdfo-1 is severely affected in meiotic prophase I. DFO encodes a protein without any known conserved domain. There was no homologue identified outside the plant kingdom, indicating that AtDFO is a plant-specific protein. AtMRE11 has been reported to be responsible for processing SPO11-generated DSBs. The Atmre11 mutant displays chromosome fragmentation during meiosis. However, the Atdfo Atmre11 double mutant had no such chromosome fragmentation, indicating that AtDFO is required for DSB formation.