A Newly Characterized Phytomelatonin Transporter Promotes Tolerance Against Multiple Inorganic Pollutants in Nicotiana benthamiana

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Abstract
Melatonin is a known pleiotropic antioxidant and signaling molecule, found in both plants and animals. Although melatonin was found to translocate via the human glucose transporter 1 (GLUT1), any mechanism of transporter‐mediated uptake of melatonin has remained unknown in plants. In the present manuscript, we found an orthologue of GLUT1 in tobacco and established its role as a functional phytomelatonin transporter (MelT) using fluorescence tracking, via melatonin‐conjugated quantum dot nanoparticles. Overexpression of NtMelT in the model plant Nicotiana benthamiana showed increased uptake of the conjugated nanofluorophores to a maximum of 5.4‐fold in roots and 2.1‐fold in leaves, while application of N ‐ethylmaleimide (inhibitor of glucose transporter) suppressed their translocation. This ensured the specificity of NtMelT for transporting melatonin. Due to increased uptake and distribution, the transgenic lines maintained a maximum of 4.6‐fold more endogenous melatonin. The transgenics were tolerant against arsenic, copper, lead, nickel, and fluoride toxicity. Increased activity of the enzymatic antioxidants detoxified excess reactive oxygen species and alleviated the associated physiological injuries. Translocation of melatonin significantly reduced bioaccumulation of the toxic pollutants and ensured normal flowering and seed setting in the transgenic plants. Overall, the present research provides a solution for safe rice cultivation under polluted environment.

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