Involved in the promotion of spontaneous somatic homologous recombination (HR) events, which is opposite to the function of FANCM in ordered HR. Only FANCM is essential for replicative repair in the absence of the endonuclease MUS81 (PubMed:24635147). Acts in the same pathway as FANCM to restrain class II meiotic crossing over (CO), and acts with FANCM during meiosis to repair interstrand cross-links (ICLs) (PubMed:24635147, PubMed:25038251). This common pathway between MHF1 and FANCM is in parallel to the pathway that involves the RECQ4A helicase (PubMed:24635147). No visible phenotype under normal growth conditions, but mutant plants exhibit a defect in somatic homologous recombination. Belongs to the TAF9 family. CENP-S/MHF1 subfamily.