Arabidopsis thaliana FANCONI ANAEMIA I (FANCI) has roles in the repair of interstrand crosslinks and CRISPR-Cas9 induced DNA double strand breaks.

DNA repair is crucial for genome stability, in particular for plants which are exposed to high levels of damage arising from UV irradiation, soil pollutants and reactive oxygen species. Damage that affects both strands of the DNA duplex is harder to repair due to both the lack of a template strand and the potential for physical separation of fragmented chromosomes. As such, DNA double-strand breaks (DSBs) and interstrand DNA crosslinks (ICL) are particularly cytotoxic forms of damage. Here we report the functions of FANCONI ANAEMIA I (FANCI), an Arabidopsis thaliana homologue of the mammalian ICL repair protein. We show that in plant cells, as in mammals, FANCI forms a nuclear localised complex with FANCD2. Genetic analysis of plants lacking FANCI displays significant hypersensitivity to the DNA crosslinking reagent mitomycin C. Furthermore, mutation of FANCI in combination with mutations in a second ICL repair factor, METHYL METHANESULFONATE AND UV-SENSITIVE PROTEIN 81 (MUS81), results in increased levels of programmed cell death compared to the corresponding single mutants, revealing roles in maintaining plant genome stability. Sequence analysis of mutational repair of CRISPR-Cas9-induced DSBs revealed that FANCI promotes single nucleotide insertions and reduces longer deletions. This pattern of mutations may reflect roles for FA proteins in replication-coupled repair of a subset of DSBs. Taken together, this analysis finds evidence for multiple roles for FANCI in the maintenance of plant genome stability.