An Overexpressed Q Allele Leads to Increased Spike Density and Improved Processing Quality in Common Wheat (Triticum aestivum)

Spike density and processing quality are important traits in the modern wheat production that is controlled by multiple gene loci. The associated genes have been intensively studied and new discoveries have been constantly reported during the past few decades. However, no gene playing significant roles in the development of these two traits was identified. In the current study, a common wheat mutant with extremely compact spikes and good processing quality was isolated and characterized. A new allele (Q^c1) of Q gene (an important domestication gene) responsible for the mutant phenotype was cloned and the molecular mechanism for the mutant phenotype was studied. Results revealed that Q^c1 was originated from a point mutation that interferes with the miRNA172-directed cleavage of the Q transcripts, leading to its overexpression. It also reduces the longitudinal cell size of rachises, resulting in an increased spike density. Furthermore, Q^c1 increases the number of vascular bundles, which suggests a higher efficiency in the transportation of assimilates in the spikes of the mutant than that of WT. This accounts for the improved processing quality. The effects of Q^c1 on spike density and wheat processing quality were confirmed by analyzing nine common wheat mutants possessing four different Q^c alleles. These results deepen our understanding of the key roles of Q gene and provide new insights for the potential application of Q^c alleles in wheat quality breeding.

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