A WAX INDUCER1/SHINE transcription factor controls cuticular wax in barley

All land plants seal their above ground body parts with a lipid-rich hydrophobic barrier called the cuticle that protects tissues from dehydration and other terrestrial threats. Mutational studies in several model species, including barley, have resolved multiple loci regulating cuticular metabolism and development. Of particular importance are the eceriferum (cer) mutants characterized by visual alterations in cuticular wax. In barley, some cer mutants, such as cer-x lines, show defects in the distinctive {beta}-diketone-enriched wax bloom on reproductive stage leaf sheaths, stems and spikes. In our study we exploited extensive allelic populations, near-isogenic lines and powerful genotyping platforms to identify variation in the HvWAX INDUCER1 (HvWIN1) gene as causal for cer-x mutants. We show that HvWIN1 function reduces cuticular permeability, promotes the accumulation of {beta}-diketones, and regulates cuticular metabolic gene expression. Analyses across the barley pangenome and hundreds of exome-capture datasets revealed high sequence conservation of HvWIN1 but also two non-synonymous variants exclusive to cultivated germplasm. Taken together, we suggest that variation in HvWIN1 controls multiple cuticular features in barley by controlling the expression of genes involved in cuticle development.