Fine-mapping and validation of Gpc-5B as the locus responsible for increases in the grain protein content, grain size, and spike density in common wheat (Triticum aestivum L.)

Abstract Grain protein content (GPC), grain size, and spike morphology are important traits for common wheat (Triticum aestivum) breeding. However, few genes positively regulating these three traits have been reported. In this study, the gene responsible for increases in GPC, grain size, and spike density in the mutant S-Cp2 were mapped and cloned. This mutant was obtained by treating the common wheat cultivar ‘Shumai482’ with ethyl methanesulfonate (EMS). According to a genetic analysis, the increases in GPC and grain size and the formation of compact spikes in S-Cp2 were controlled by a single dominant locus (Gpc-5B) on chromosome 5BL. This locus was mapped to an 87.24 kb interval between markers KASP-58070 and KASP-58158, wherein 5Bq (homologous to Q on chromosome 5AL) was detected. One missense mutation (G-to-A) was detected within the microRNA172-binding site of 5Bq in S-Cp2 (i.e., 5BQ4 allele), suggesting that 5Bq is responsible for the mutant phenotype. This was confirmed by cloning 5Bq in revertants obtained by treating S-Cp2 with EMS. As expected, 5BQ4 in S-Cp2 was significantly more highly transcribed than 5Bq in ‘Shumai482’. Notably, 5Bq was positively selected during breeding. The study findings reflect the value of 5Bq for breeding novel wheat varieties.