N-Acetylglutamic Acid Enhances Tolerance to Oxidative and Heat Stress in Humulus lupulus

Abstract

Humulus lupulus (hop) is a necessary material in beer brewing because its female inflorescences (called hop cones) give a floral aroma, bitterness and foam stability to beer. Various aspects of growth conditions in the cultivation area, especially temperature, strongly affect the yield and quality of hop cones. Recent estimates suggest that climate change accompanied by global warming is negatively impacting hop production, with high temperatures reducing the expression of genes that regulate beneficial secondary metabolites in hops. This underscores the need for techniques to enhance hop tolerance to high temperatures. This study explores the potential of N-acectylglutamic acid (NAG), a non-proteinogenic amino acid, to confer hops with tolerance against oxidative and heat stress by suppressing ROS accumulation. Exogenous NAG treatment activated the expression of HlZAT10/12 and HlHSFA2, which are putative homologues considered master regulators in response to oxidative and heat stress in Arabidopsis thaliana (Arabidopsis). Additionally, histone acetylation, a histone modification associated with transcriptional activation, was increased at these stress-responsive genes in the NAG-treated hops. These findings reveal NAG as a potential chemical compound to mitigate hop production reduction caused by high temperatures and suggest the conservation of epigenetic modification-mediated regulation of gene expression in response to environmental stresses in hops.