Defense mechanism of tea plant (Camellia sinensis L.) to tolfenpyrad reveals emerging role of melatonin in pesticide residue control

Excessive use of pesticides has raised great concern on food safety as well as crop quality in the form of pesticide residues. Plants have natural defense mechanisms against pesticides for its alleviation. This study investigated distribution of tolfenpyrad as well as physiological, metabolomic, transcriptomic and hormonal responses of tea plants to tolfenpyrad application. Results show that tolfenpyrad tends to accumulate in tea leaves, with limited translocation to stems and roots after foliar application. While no significant change in plant biomass or growth status was apparent following tolfenpyrad application, it triggered reactive oxygen species (ROS) and antioxidant system impacts. Metabolomic and transcriptomic analyses reveal disrupted purine metabolism and nitrogen metabolism, mainly in amino acid pathways, with a glutathione (GSH) detoxification response. Hormonal and targeted metabolic profiling confirms a significant elevation in melatonin biosynthesis, then exogenous application of melatonin is proved to efficiently reduce pesticide residue in tea plants. This study improved our understanding of the tea plants' defense mechanism to pesticide, and suggested an emerging plant-derived regulator for improving quality and safety of tea products.