Melatonin enhanced photosynthesis efficiency by improving carotenoid biosynthesis and carbon fixation via regulation of transcription factors

Melatonin enhances photosynthesis efficiency in high plants. However, the underlying molecular mechanism remain largely unexplored. Our study provides novel insights into the multifaceted role of melatonin in Nicotiana tabacum, an important industrial crop. Foliar application of melatonin improved the photosynthetic capacity, promoted antioxidant enzymes activity, and enhanced tolerance to reactive oxygen species (ROS). Compared with control, melatonin-treated tobacco exhibited the increase in carotenoid contents including lutein, β-carotene, neoxanthin and violaxanthin, along with the higher levels of chlorophyll a and chlorophyll b. RNA-seq analysis indicated that melatonin robustly stimulated pathways related to carotenoid biosynthesis, biosynthesis of amino acids, photosynthesis, carbon fixation in photosynthetic organism, fatty acid biosynthesis, and glutathione metabolism. Co-expression network indicated the melatonin activated key transcription factors, including bHLH, WRKY, MYB, NAC, MADS6 and AP2/ERF. These transcription factors likely enhanced carotenoid biosynthesis and carbon fixation. Our results highlight the potential of melatonin as a novel eco-friendly agrochemical. Its application could address agricultural challenges by improving photosynthetic efficiency, thereby offering a sustainable solution for crop enhancement.