Compositional variances in cuticular lipids of wild and domesticated barley leaves and their impact on plant-environment interactions

One of the oldest cereal crops, barley is thought to have been domesticated similar to 8000 years ago, in the Fertile Crescent. In this study, we explored the overlooked contribution of cuticular lipid metabolism to barley domestication by comparatively characterizing wild and domesticated barley variants. We revealed substantial phenotypic variances in plants' overall morphology and in vegetative and reproductive tissues. Multiple microscopic approaches combined with gas chromatography-mass spectrometry (GC-MS) metabolite profiling indicated that wild barley leaves are more densely covered with epicuticular waxes compared to domesticated leaves with distinct compositions, but both variants contain a similar cuticle ultrastructure. Gene expression assays corroborated these observations showing higher transcript expression of key epicuticular wax biosynthetic genes in wild barley leaves, but similar expression patterns of cutin biosynthetic genes in leaves of both cultivars. Wild barley leaves also transpired water at higher rates apparently due to higher stomata density and conductance. Previous evidence claimed that barley leaf epicuticular waxes shape the interactions with Blumeria graminis f.sp. hordei (Bgh), the causal agent of powdery mildew in barely. However, in-vivo and in-vitro inoculation assays inferred that the disparate wax content and composition in wild and domesticated leaves had no apparent effect on Bgh pre-penetration processes. Altogether, our data provide novel insight into the compositional variances in cuticular lipids of wild and domesticated barley leaves and their impact on plant-environment interactions.