Phenotypic and transcriptomic characterization of OsSWEET14-edited rice (cv. Samkwang) with enhanced bacterial blight resistance

Background: Bacterial blight (BB) caused by Xanthomonas oryzae pv. oryzae (Xoo) poses a serious threat to rice production. The pathogen promotes infection by targeting effector binding elements in the promoter regions of rice susceptibility genes such as SWEET (Sugars Will Eventually be Exported Transporters) genes. Previous studies have shown that natural or induced variations in SWEET genes can effectively enhance BB resistance in rice. However, the effects of variations in SWEET genes on disease resistance and agronomic performance vary depending on the Xoo strains and the genetic background of rice cultivars, highlighting the need for precise evaluations in breeding applications. Results: In this study, we developed a CRISPR/Cas9-edited OsSWEET14 knockout line (SK-s14) in the background of the elite Korean rice cultivar Samkwang. The SK-s14 line exhibited enhanced resistance against the Xoo strain KACC10859. Transcriptomic analysis revealed that defense-related genes, including pathogenesis-related genes and salicylic acid signaling genes, were downregulated in SK-s14 relative to Samkwang under Xoo inoculation. These results suggest that the enhanced resistance may result from pathogen starvation due to restricted sugar efflux to apoplast, rather than from classical defense activation. Field evaluations showed that SK-s14 plants headed 1–7 days earlier, had longer panicles (+ 8.0%), and exhibited modest reductions in grain weight (-3.0%) and grain fertility (-4.4%) compared to Samkwang. Conclusions: Our results show that knocking out OsSWEET14 in the Samkwang background enhances BB resistance against the KACC10859 strain, likely through a pathogen starvation mechanism. Despite a modest grain yield reduction (-7.2%) observed under field conditions, SK-s14 represents a promising breeding material for disease-prone rice growing regions.