Functional Validation of the Melon Fom-1 Gene, Controlling Resistance to Fusarium oxysporum Races 0 and 2, by...

Functional validation of NLR genes is critical for confirming their specific roles and developing durable disease-resistant crops. The Fom-1 gene of Cucumis melo, controlling resistance to races 0 and 2 of F. oxysporum f. sp. melonis (FOM), had been identified by map-based cloning as MELO3C022146, which encodes a TIR-NBS-LRR (TNL) protein. It resides in a head-to-head orientation adjacent to another TNL gene, Prv, controlling resistance to papaya ring spot virus (PRSV). In this study we validated the function of Fom-1 in mediating FOM resistance by applying CRISPR/Cas9 editing to the resistant cultivar, Védrantais. Two gRNAs were designed to target exons 1 and 2, respectively, and mutations were introduced at both target sites, resulting in truncated open reading frames in both alleles. Inoculation assays of T₁ plants with FOM races 2 and 0 revealed a breakdown of resistance, manifested by leaf necrosis and wilting, and susceptibility was stably inherited in the T₂ generation. This proved that MELO3C022146, the candidate gene for Fom-1, is responsible for resistance in melon cultivar Védrantais. Future studies will address the molecular functions of this gene as well as possible interactions between Fom-1 and its neighbour R-gene, Prv.