Abstract
Spike architecture is an indicative trait of grain yield in common wheat (Triticum aestivum). A segregating population was generated for mapping genes contributing to spike morphometric traits by crossing the two common wheat cultivars 'CItr 17600' with branching spikes and 'Yangmai 18' with normal spikes. A major quantitative trait locus for spike length was mapped to the Q5A region of chromosome 5A. Yangmai 18 carried a Q5Ab allele for short spikes, which harbored one SNP in the last intron, and a 1-bp InDel in the 720-bp fragment from the start codon, compared to Q5Aa in Chinese Spring. CItr 17600 harbored a q5Ab allele for long spikes, which has a 6-bp deletion compared to the reported q5Aa allele that was involved in the binding site of microRNA 172 (miR172). This 6-bp deletion in immediately upstream of this binding site was involved in changes of four amino acids. The natural q5A allele appeared to be rare in common wheat but frequent in tetraploid T. turgidum accessions with branching spikes. The CRISPR/Cas9 technology was used to edit the upstream region involving in the miR172 binding site in Yangmai 18 and identified two independent editing events, one with a 1-bp insertion in Q5A and the other with a 2-bp deletion in Q5D, resulting in several shapes of spikes in the transgenic progeny. In addition to the effects of natural q5A allele and the edited Q5A genes, this study indicated the regeneratability and transformability of Yangmai 18 as an elite cultivar. Altogether, this study provides insight into future modification and engineering of spike architecture in common wheat.
