The Q c5 Allele Increases Wheat Bread-Making Quality by Regulating SPA and SPR.

Common wheat ( Triticum aestivum L.) is an important food crop with a unique processing quality. The Q gene positively regulates the processing quality of wheat, but the underlying mechanism remains unclear. Here, a new Q allele ( Q c5 ) responsible for compact spikes and good bread performance was identified. Compared with the Q allele widely distributed in modern common wheat cultivars, Q c5 had a missense mutation outside the miRNA172-binding site. This missense mutation led to a more compact messenger RNA (mRNA) secondary structure around the miRNA172-binding region, resulting in increased Q c5 expression during the spike development stage and a consequent increase in spike density. Furthermore, this missense mutation weakened the physical interaction between Q c5 and storage protein activator (SPA) in seeds and suppressed the expression of storage protein repressor ( SPR ). These changes increased the grain protein content and improved the bread-making quality of wheat. In conclusion, a missense mutation increases Q expression because of the resulting highly folded mRNA secondary structure around the miRNA172-binding site. Furthermore, this mutation improves the bread-making quality of wheat by repressing the expression of SPR and influencing the physical interaction between Q and SPA. These findings provide new insights into the miRNA172-directed regulation of gene expression, with implications for wheat breeding.