Fine-tuning quantitative agronomic traits by manipulating gene copy number in rice

Although recent plant pan-genome studies have revealed extensive copy number variations, there are limited studies addressing the phenotypic consequences of these variations. Here, we manipulated the copy number of OsMADS18 in rice (Oryza sativa) through gene editing and evaluated the effects. OsMADS18, which encodes a MADS-box transcription factor known to regulate plant development, is tandemly duplicated in the elite rice cultivar Hitomebore as a natural variant. We therefore edited the OsMADS18 copy number using a basic CRISPR/Cas9 system and established rice lines harboring one to three tandem copies of OsMADS18, as identified through high throughput qPCR screening. The presence of one to three OsMADS18 tandem copies was reflected in stepwise increases in transcript levels and concomitant trait values for leaf blade length and culm length. These results demonstrate that manipulating gene copy number can fine-tune important agronomic traits, providing a novel breeding strategy for crop improvement.