Exogenously applied MT enhanced cold tolerance in tea plants by increasing fatty acid desaturation and polyamine metabolism

MT (melatonin), an important bioactive small molecule, plays crucial roles in plant responses to temperature or water stress. However, the intrinsic mechanisms underlying the modulatory effects of MT on physiological reactions are less clear. In this study, the mechanism by which exogenous MT modulates fatty acid and polyamine (PA) metabolism in tea plants under cold stress was studied. Application of 100 μM MT significantly increased the cold tolerance of tea plants. Additionally, PCPA (MT metabolic inhibitor) further aggravated cold-induced cell damage. Consistent with the change in phenotype, foliar application of MT significantly increased fatty acid unsaturation and PA levels compared with those under cold stress. In contrast, the MT metabolic inhibitor PCPA further impaired fatty acid desaturation and polyamine levels under the PCPA + cold treatment compared with those under the cold treatment. To further elucidate the role of MT in regulating fatty acid and PA metabolism, CsCOMT3 (a key enzyme in MT synthesis)-silenced tea leaves were generated via virus-induced gene silencing (VIGS). Compared with the control leaves, CsCOMT3-inhibited tea leaves presented greater wilting and weaker chlorophyll fluorescence, with lower levels of fatty acid unsaturation and PAs. Our results clearly revealed that MT application may be a feasible strategy to relieve cold injury in tea plants by enhancing fatty acid and PA metabolism.