miR172 Plays a Critical Role in the Origin of Free-Threshing Wheat

Wheat domestication from wild species involved mutations in the Q gene. The q allele (wild wheats) is associated with speltoid spikes and hulled grains, whereas the mutant Q allele (domesticated wheats) confers subcompact spikes and free-threshing seeds. Previous studies showed that Q encodes an AP2-like transcription factor, but the causal polymorphism of the domestication traits remained unclear. In this work, we show that the interaction between microRNA172 (miR172) and Q allele is reduced by an SNP in the miR172 binding site. Besides, the inhibition of miR172 activity in transgenic wheat by a miRNA target mimic approach resulted in compact spikes. By contrast, overexpression of miR172 was sufficient to induce speltoid spikes and non-free-threshing seeds, similar to those observed in three loss-of-function mutations in the Q gene. We propose that the cleavage of AP2-like transcripts by miR172 promotes wild characters and that selection of a nucleotide change at the miR172 binding site of the Q gene contributed to subcompact spikes and free-threshing seeds during wheat domestication.