Mapping and gene cloning of a wheat mutant <i>dsc</i> with dwarf and compacted spikes.

Plant height and spikelet density are two important traits for wheat (<i>Triticum aestivum</i> L.) yield. The development of wheat mutants not only provides new genetic resources for wheat improvement but also facilitates our understanding of the molecular regulation of these traits. Previously, we obtained a mutant named dwarf and spike compactness (<i>dsc</i>) from wheat cultivar Guomai301 (wild type, WT) treated with ethyl methane sulphonate. This study investigates the heredity, mutated gene location, and the candidate gene of <i>dsc</i>. Highresolution chromosome painting analysis indicated that there were no visible structural variations in the mutant <i>dsc</i>. Genetic analysis indicated that the phenotype of dsc was controlled by a single dominant gene, named as <i>dsc</i>. The wheat 660 K single-nucleotide polymorphism (SNP) array and simple sequence repeat (SSR) marker assay were employed to map the mutated gene. A total of 984 SNPs were identified between the DNA bulks, among which, 492 SNPs were located on chromosome 5A in 580-680 Mb genomic region, which occupied 50% of the total SNPs. The gene <i>dsc</i> was mapped in a 33.4 Mb (625.7-659.1 Mb) region on chromosome arm 5AL, flanked by SSR markers <i>Xbarc319</i> and <i>Xgpw2136</i>, where <i>5AQ</i> is located. Sequences and expression patterns of <i>5AQ</i> from WTand dsc were compared. The two <i>5AQ</i>s had a SNP (G>A) in the <i>miR172</i> binding site. A dCAPS marker was developed based on the SNP, and the marker was cosegregated with the mutated phenotypes in a F_2:3 population derived from the cross <i>dsc</i> x Chinese Spring (CS). This result demonstrated that the gene <i>5AQ</i> was the mutated gene of <i>dsc</i>. The expression levels of <i>5AQ</i> were significantly higher in roots, stems, leaves and spikes of mutant <i>dsc</i> than those in WT. Our results demonstrated that point mutation in the <i>miR172</i> binding site of the <i>5AQ</i> likely increased its transcript level via a reduction in miRNA-dependent degradation, and this resulted in pleiotropic effects on spikelet density and plant height. Obviously, <i>miR172</i>-<i>Q</i> was a key regulation module for wheat growth and spike development. The dCAPS marker could be used to detect the elite allele of <i>Q</i> in wheat breeding. Regulation of <i>miR172</i>-<i>Q</i> module might be an approach for wheat yield breeding.