Functional 5Bq allele is responsible for the compact spike phenotype in common wheat (Triticum aestivum L.)

Spike morphology is an important characteristic of common wheat because of its effects on yield potential. However, few available genes regulating spike morphology have been reported in common wheat. We identified a compact spike mutant S-Cp2, which was obtained by treating common wheat cultivar ‘Shumai482’ with ethyl methanesulfonate. The gene responsible for the compact spike phenotype of S-Cp2 was mapped and cloned. According to a genetic analysis, the formation of a compact spike in S-Cp2 was controlled by a single dominant locus (Cs-5B) on chromosome 5BL. This locus was mapped to an 87 kb interval between markers KASP-58070 and KASP-58158, wherein 5Bq gene was detected. One missense mutation was called within the microRNA172-binding site of 5Bq in S-Cp2, suggesting that the mutated 5Bq allele (5BQ4) is responsible for the compact spike phenotype. This was confirmed by cloning 5Bq in revertants obtained by treating S-Cp2 with ethyl methanesulfonate. As expected, the 5BQ4 allele was expressed at significantly higher levels than the 5Bq allele in developing spike tissues. According to a haplotype analysis, the functional haplotype 1 for 5Bq was gradually accumulated in modern Chinese wheat cultivars. In this study, we identified a functional 5Bq allele by genetic mapping, which was responsible for the compact spike phenotype in mutant S-Cp2. The study findings highlight the potential utility of 5Bq for breeding novel wheat cultivars.