The dual roles of melatonin biosynthesis enzymes in the coordination of melatonin biosynthesis and autophagy in cassava.

Both autophagy and melatonin play important roles in plant development and stress response. However, the direct correlation between autophagy and melatonin as well as the underlying mechanism remains elusive in plants. In this study, we discovered that the expression of three autophagy-associated genes (MeATG8b, 8c, and 8e) and autophagic activity were induced by exogenous melatonin treatment in cassava. In addition, three melatonin biosynthesis enzymes (tryptophan decarboxylase 2 (MeTDC2), N-aceylserotonin O-methyltransferase 2 (MeASMT2), and MeASMT3) positively regulate endogenous melatonin level and autophagic activity. Further investigation showed that these melatonin biosynthesis enzymes interacted with MeATG8b/8c/8e in vivo and in vitro. Consistently, MeTDC2, MeASMT2, and MeASMT3 also positively regulate endogenous melatonin level and autophagic activity in cassava. Notably, overexpression of MeATG8b, 8c, and 8e facilitated the protein expression level of MeTDC2, MeASMT2, and MeASMT3 in vivo. Taken together, melatonin synthesis enzymes (MeTDC2, MeASMT2/3) interact with MeATG8b/8c/8e and thus coordinate the dynamics of melatonin biosynthesis and autophagic activity in cassava, highlighting the links between melatonin biosynthesis and autophagic activity in cassava.