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

Summary 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 (Ta TPL ). 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 Ta TPL . 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 Ta TPL in controlling the bread wheat spike architecture.