FANCM interacts with the MHF1-MHF2 complex to limit crossover frequency during rice meiosis

Crossovers (COs) are necessary for generating genetic diversity that breeders can select, but there are conserved mechanisms that regulate their frequency and distribution. Increasing CO frequency may raise the efficiency of selection by increasing the chance of integrating more desirable traits. In this study, we characterize rice FANCM and explore its functions in meiotic CO control. FANCM mutations do not affect fertility in rice, but they cause a great boost in the overall frequency of COs in both inbred and hybrid rice, according to genetic analysis of the complete set of fancm zmm (hei10, ptd, shoc1, mer3, zip4, msh4, msh5, and heip1) mutants. Although the early homologous recombination events proceed normally in fancm, the meiotic extra COs are not marked with HEI10 and require MUS81 resolvase for resolution. FANCM depends on PAIR1, COM1, DMC1, and HUS1 to perform its functions. Simultaneous disruption of FANCM and MEICA1 synergistically increases CO frequency, but it is accompanied by nonhomologous chromosome associations and fragmentations. FANCM interacts with the MHF complex, and ablation of rice MHF1 or MHF2 could restore the formation of 12 bivalents in the absence of the ZMM gene ZIP4. Our data indicate that unleashing meiotic COs by mutating any member of the FANCM-MHF complex could be an effective procedure to accelerate the efficiency of rice breeding.