WAX INDUCER 1 Regulates β-Diketone Biosynthesis by Mediating Expression of the Cer-cqu Gene Cluster in Barley

Abstract

Plant surface properties are crucial determinants of resilience to abiotic and biotic stresses. The outer layer of the plant cuticle consists of chemically diverse epicuticular waxes. The WAX INDUCER1/SHINE subfamily of APETALA2/ETHYLENE RESPONSIVE FACTORS regulates cuticle properties in plants. In this study, four barley genes homologous to the <i>Arabidopsis thaliana AtWIN1</i> gene were mutated using RNA-guided Cas9 endonuclease. Mutations in one of them, the <i>HvWIN1</i> gene, caused a recessive glossy sheath phenotype associated with β-diketone deficiency. A complementation test for <i>win1</i> knockout (KO) and <i>cer-x</i> mutants showed that <i>Cer-X</i> and <i>WIN1</i> are allelic variants of the same genomic locus. A comparison of the transcriptome from leaf sheaths of <i>win1</i> KO and wild-type plants revealed a specific and strong downregulation of a large gene cluster residing at the previously known <i>Cer-cqu</i> locus. Our findings allowed us to postulate that the WIN1 transcription factor in barley is a master mediator of the β-diketone biosynthesis pathway acting through developmental stage- and organ-specific transactivation of the <i>Cer-cqu</i> gene cluster.