Barley HvBODYGUARD1 controls cuticular specialisations regulated by SHINE transcription factors.

Land plants secrete a protective outer cuticular layer with diverse functions. Barley (Hordeum vulgare L.) develops two cuticular specialisations: the β-diketone rich wax bloom on vegetative tissues and an adherent grain surface which sticks to the hulls, leading to barley's distinctive 'covered' grain phenotype. Two barley SHINE transcription factors, HvWIN1 and NUD, promote the wax bloom and covered grain phenotypes, respectively, yet we know little about other genes involved. We investigated a barley mutant showing defects in both cuticular specialisations to better understand the networks and processes underlying these traits. We identified the barley BODYGUARD1 (HvBDG1) gene encoding an α/β hydrolase as crucial for leaf cuticular integrity and wax-bloom deposition. Mining tetraploid wheat (Triticum turgidum ssp. durum) mutant populations demonstrated that BDG1 and WIN1 orthologues also control the wax bloom in wheat. We further reveal that NUD and HvWIN1 retain functional, independent overlap in leaf cuticle integrity and hull adhesion in barley, functions which involve upregulation of HvBDG1 and other direct or indirect targets, shared and distinct, depending on the stage and tissue. Our work greatly expands our knowledge of genetic and developmental mechanisms underlying shared and distinctive cuticular features in plants.