The wheat transcription factor Q functions in gibberellin biosynthesis and signaling and regulates height and spike length

The Q gene is a key domestication gene in wheat (Triticum aestivum) that regulates free-threshing habit, spike morphology, height, and other critical agronomic traits. However, the precise molecular mechanisms underlying its function remain unclear. In this study, we identified a Q allele with a missense mutation (G to A) in the fifth exon of the Q gene, resulting in reduced plant height and spike length. Further investigation revealed that this mutation causes a Gly-229-Ser amino acid substitution, which enhances Q protein stability. Furthermore, we discovered that Q directly binds to the promoter region of Gibberellin 3-oxidase 2 gene (TaGA3ox2) and represses its expression. Moreover, Q interacts with both REDUCED HEIGHT1 (RHT1) and GIBBERELLIN INSENSITIVE 2 (TaGID2), which may disrupt GID2-triggered RHT1 degradation. Collectively, these findings reveal the dual roles of Q in regulating both GA biosynthesis and signaling, providing insights into the molecular mechanisms through which Q modulates plant height and spike length in wheat.