SPR9 encodes a 60 S ribosomal protein that modulates panicle spreading and affects resistance to false smut in rice (Oryza sativa. L)

The architecture of inflorescence in crops is a key agronomic feature determining grain yield and thus has been a major target trait of cereal domestication. In this study, we show that a simple spreading panicle change in rice panicle shape, controlled by the Spreading Panicle 9 (SPR9) locus, also has a significant impact on the resistance to rice false smut (RFS). Meanwhile, we mapped a novel spr9 mutant gene between markers Indel5-18 and Indel5-22 encompassing a genomic region of 43-kb with six candidate genes. Through gene prediction and cDNA sequencing, we confirmed that LOC_Os05g38520 is the target gene in the spr9 mutant, which encodes 60 S ribosomal protein L36-2. Further analysis showed that the spr9 mutant is caused by a 1 bp deletion in the first exon that resulted in premature termination. Knockout experiments showed that the SPR9 gene is responsible for the spreading panicle phenotype of the spr9 mutant. Interestingly, the spr9 mutant was found to improve resistance to RFS without affecting major agronomic traits. Taken together, our results revealed that the spr9 allele has good application prospects in rice breeding for disease resistance and panicle improvement. We report the map-based cloning and functional characterization of SPR9, which encodes a 60 S ribosomal protein that regulates spreading panicles and affects the resistance to false smut in rice.