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

Although plant pan-genome studies have revealed extensive copy number variations, their phenotypic consequences remain poorly understood. Here, we manipulated the copy number of OsMADS18 in rice (Oryza sativa) cv 'Hitomebore' using the CRISPR/Cas9 system. We established rice lines harboring one to three tandem copies of OsMADS18, as identified by quantitative PCR and sequencing. The presence of one to three OsMADS18 tandem copies was reflected in stepwise increases in transcript levels and concomitant agronomic trait values. These results demonstrate that manipulating gene copy number can fine-tune important quantitative traits, providing a novel breeding strategy for crop improvement.