Genome-Wide Association Study to Identify Bakanae Disease Resistance- Related QTLs Carrying Novel Candidate Genes in Rice (Oryza sativa L.)

Bakanae disease is a rice disease whose importance is increasing considerably in several rice-growing countries, leading to incremental production losses. In this study, qBK9 was identified via GWASs based on 169 Korean landrace accessions. Furthermore, 5 genes in the qBK9 region were identified as potential candidates, which demonstrated notable expression differences between resistant and susceptible accessions. Finally, OsUBC18 encoded a ubiquitin-conjugating enzyme significantly downregulated in the resistant rice cultivars. Os UBC18 T-DNA insertion mutants presented significantly reduced bakanae resistance. A single nucleotide polymorphism (SNP) in the promoter region of OsUBC18 is responsible for its differential expression, leading to alterations in rice bakanae resistance. Moreover, genes associated with the gibberellin (GA) pathway, which plays a role in bakanae disease, were down-regulated in OsUBC18 T-DNA mutant lines. These findings suggest that OsUBC18 is a gene associated with bakanae resistance, and its expression enhances rice immunity via reduced GA-related genes.