Wax-on, Wax-Off: ncRNA Mediate Control of Glaucousness in Wheat

Diketone surface waxes accumulate in wheat and other Triticeae during development to produce the blue-white glaucous trait associated with increased stress tolerance. Glaucousness in durum wheat is controlled by a metabolic gene cluster at the Wax 1 (W1) locus and a dominant suppressor Inhibitor of wax 1 (Iw1) on chromosome 2B. In bread wheat, the D subgenome from progenitor Aegilops tauschii contains W2 and Iw2 paralogs on 2D. We have identified the Iw1 gene from durum wheat and demonstrate the unique regulatory mechanism by which Iw1 acts to suppress a carboxylesterase-like protein gene, W1-COE, within the W1 multigene locus. Iw1 is a novel lncRNA which forms a long hairpin and produces a 21-nucleotide predominant miRNA, miRW1, and smaller numbers of related sRNAs. When the Iw1 gene was introduced into glaucous bread wheat, we observed accumulation of miRW1 and associated sRNAs, down-regulation of W1-COE and its paralog W2-COE, and consequently a β-diketone-depleted non-glaucous phenotype. Iw1 has homology to a region on chromosome 2 in Ae. tauschii that lies within the marker-based location of Iw2. We propose the Iw loci arose from inverted duplication of its target gene in ancestral wheat to form lncRNA with the characteristics of young miRNA genes that ultimately act to selectively supress the glaucous trait.