Tobacco HY5, NtHY5, positively regulates flavonoid biosynthesis and enhances salt stress tolerance

Abstract

ABSTRACTPlants have evolved complex signaling networks to regulate their growth and development. Some of these signaling components also play a crucial role in secondary metabolite biosynthesis. Among the signaling components identified to date, ELONGATED HYPOCOTYL 5 (HY5), a bZIP family transcription factor is the most investigated and known as the center of transcriptional network hub. However, HY5 has not been characterized from plants known to synthesize important secondary metabolites. In this study, based on homology search and phylogenetic analysis, HY5 has been identified from Nicotiana tobaccum, and characterized for its role in secondary plant product biosynthesis and stress response through developing overexpressing lines and CRISPR/Cas9-based knockout mutant plants. NtHY5 was able to complement the Arabidopsis thaliana hy5 mutant at molecular, morphological and biochemical levels. Overexpression of NtHY5 in tobacco led to the up-regulation of the phenylpropanoid pathway genes and enhanced the flavonoid content, whereas mutant plants had the opposite effect. Electrophoretic Mobility Shift Assay (EMSA) suggested that NtHY5 interacts with the promoter of NtMYB12, a transcription factor known to regulate flavonoid biosynthesis. In addition, NtHY5 enhanced the abiotic stress tolerance as evident by the salt tolerance ability of HY5 overexpressing lines by diminishing the ROS accumulation after salt treatment. These data provide credible evidence about the potential role of NtHY5 in light-mediated flavonoid biosynthesis, plant growth and abiotic stress tolerance in tobacco. The photomorphogenic mutant, Nthy5, developed in this study, will help in elucidating the role of the HY5 in different biological processes in tobacco.One sentence summaryAnalysis of NtHY5 overexpressing and mutant plants suggests role of NtHY5 in flavonoid biosynthesis and salt stress tolerance.