Knockout of RRS1 Enhances Culm Mechanical Strength and Grain Yield in Rice

Lodging decreases crop yields, but a strong stem improves lodging resistance in grains such as rice (Oryza sativa). In this study, we determined that the R2R3-type MYB transcription factor Robust Root System 1 (RRS1) negatively regulates culm mechanical strength in rice by affecting culm diameter and culm wall thickness. Specifically, RRS1 reduces culm diameter by directly activating STRONG1 expression, which in turn alters cellulose deposition and sclerenchyma cell wall development. Knocking out RRS1 improved culm mechanical strength and increased yield while maintaining quality, highlighting its considerable value for rice breeding. The favourable RRS1 allele (RRS1^Hap5) has great potential as a target for improving lodging resistance in rice. Combined haplotype analysis showed that plants with group II haplotypes, comprising the two elite alleles of RRS1 and STRONG1, exhibited the largest culm diameter in both indica and japonica rice. Furthermore, the japonica rice accessions harbouring the two elite alleles of RRS1 and STRONG1 exhibited the highest grain number per panicle. Thus, this study presents a valuable gene aggregation strategy for the simultaneous improvement of lodging resistance and grain yield in japonica rice.