Identification of a candidate rice blast resistance gene, (t), in an introgression line of using CRISPR/Cas9-mediated genome editing.

Resistance breeding for rice blast is an economic strategy for protecting rice crops against this disease. Genes with nucleotide-binding site leucine-rich repeat (NBS-LRR) structures are known to contribute to disease resistance. Here, we identified a candidate resistance gene, named (t), associated with leaf and panicle blasts in an introgression line carrying the chromosome 4 segment of wild rice ( Griff.) backcrossed with the cultivar 'Nipponbare' ( L.). Mapping analysis based on leaf blast severity confirmed that (t) was localized in the 177-kb NBS-LRR cluster region. To identify the (t) sequence, mutant lines were generated by knocking out a candidate NBS-LRR gene in a homozygous line carrying (t), M18, using CRISPR/Cas9-mediated genome editing. Leaf blast resistance was lost in the mutant lines lacking the corresponding Os04g0620950 N-terminal sequence of the M18 line. The result suggested that the counterpart NBS-LRR gene in the M18 line is involved in resistance to leaf blast. (t) showed homology to in the resistant cultivar 'Kahei', and an NBS-LRR gene in the resistant cultivar 'Mine-haruka' carrying (t). These results suggest that the NBS-LRR gene is a candidate gene of (t) and is present on the long arm of chromosome 4.