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microRNA172 plays a crucial role in wheat spike morphogenesis and grain threshability

Debernardi, Juan Manuel, Lin, Huiqiong, Faris, Justin D., Dubcovsky, Jorge, Chuck, George
Development 2017 v.144 pp. 1966-1975
Triticum aestivum, alleles, binding sites, domestication, florets, gene overexpression, microRNA, morphogenesis, mutants, single nucleotide polymorphism, transcription (genetics), transcription factors, wheat, wild relatives
Wheat domestication from wild species involved mutations in the Q gene. The q allele (wild wheats) is associated with elongated spikes and hulled grains, whereas the mutant Q allele (domesticated wheats) confers subcompact spikes and free-threshing grains. Previous studies showed that Q encodes an AP2-like transcription factor, but the causal polymorphism of the domestication traits remained unclear. Here, we show that the interaction between microRNA172 (miR172) and the Q allele is reduced by a single nucleotide polymorphism in the miRNA binding site. Inhibition of miR172 activity by a miRNA target mimic resulted in compact spikes and transition from glumes to florets in apical spikelets. By contrast, overexpression of miR172 was sufficient to induce elongated spikes and non-free-threshing grains, similar to those observed in three Q loss-of-function mutations. These lines showed transitions from florets to glumes in the basal spikelets. These localized homeotic changes were associated with opposing miR172/Q gradients along the spike. We propose that the selection of a nucleotide change at the miR172 binding site of Q contributed to subcompact spikes and free-threshing grains during wheat domestication.