Effect of low root-zone temperature and UV radiation on growth and gene expression of secondary metabolite pathways in Nicotiana benthamiana

•Low root-zone temperature and UV radiation affect several metabolic pathways related to secondary metabolite biosynthesis.•Major secondary metabolite activities were the activation of terpenoid and nicotine biosynthesis.•Combined treatment improved the quality traits of N. benthamiana. The current study explored the effects of low root-zone temperature (LT) and UV radiation (UV) alone and combined on changes in growth, transcription, and gene expression related to secondary metabolite production. Nicotiana benthamiana plants were grown in a controlled environment (25/20°C, 16/8 h [light/dark], 70% relative humidity, 1,000 µmol·mol−1 CO2 with photosynthetic photon flux densities of 100 and 200 µmol·m−2·s−1 for 10 and 18 d, respectively). Twenty-eight days after sowing, these plants were treated with LT (15°C), 0.3 W·m−2 of UV radiation, and a combined treatment with LT and UV (LT*UV) for 3 d. Results found that the treatment with UV alone decreased the quantum efficiency of photosystem II by approximately 1.5 times, and most growth characteristics decreased under the UV (approximately 1.5 times) and LT*UV (approximately 2 times) treatments. Treatment with LT*UV significantly inhibited the growth characteristics and photosynthetic rates compared to those under the single LT and UV treatments. Changes in the transcriptome of plants in response to different environmental conditions were determined based on the expression levels of genes related to secondary metabolites and microarrays. In particular, the transcriptome levels of phenylpropanoid and flavonoid biosynthesis were the most significantly affected by LT*UV. This suggests the potential of using LT treatment in hydroponic systems and UV radiation to control the synthesis of health-promoting compounds of secondary metabolites in greenhouses and controlled-environment agricultural facilities.