Functional regulation of Q by microRNA172 and transcriptional co‐repressor TOPLESS in controlling bread wheat spikelet density

Bread wheat (Triticum aestivum) spike architecture is an important agronomic trait. The Q gene plays a key role in the domestication of bread wheat spike architecture. However, the regulatory mechanisms of Q expression and transcriptional activity remain largely unknown. In this study, we show that overexpression of bread wheat tae‐miR172 caused a speltoid‐like spike phenotype, reminiscent of that in wheat plants with the q gene. The reduction in Q transcript levels in the tae‐miR172 overexpression transgenic bread wheat lines suggests that the Q expression can be suppressed by tae‐miR172 in bread wheat. Indeed, our RACE analyses confirmed that the Q mRNA is targeted by tae‐miR172 for cleavage. According to our analyses, the Q protein is localized in nucleus and confers transcriptional repression activity. Meanwhile, the Q protein could physically interact with the bread wheat transcriptional co‐repressor TOPLESS (TaTPL). Specifically, the N‐terminal ethylene‐responsive element binding factor‐associated amphiphilic repression (EAR) (LDLNVE) motif but not the C‐terminal EAR (LDLDLR) motif of Q protein mediates its interaction with the CTLH motif of TaTPL. Moreover, we show that the N‐terminal EAR motif of Q protein is also essentially required for the transcriptional repression activity of Q protein. Taken together, we reveal the functional regulation of Q protein by tae‐miR172 and transcriptional co‐repressor TaTPL in controlling the bread wheat spike architecture.