Melatonin Antagonizes Jasmonate-Triggered Anthocyanin Biosynthesis in Arabidopsis thaliana

As a plant-specific flavonoid type metabolite, anthocyanin is an important plant-sourced nutrition. Although the anthocyanin biosynthesis pathway has been revealed, how to modulate anthocyanin production by endogenous molecules is still elusive. Here, we investigated the role of melatonin in anthocyanin biosynthesis in the reference plant Arabidopsis thaliana and found that melatonin suppresses anthocyanin synthesis. Moreover, melatonin was able to significantly inhibit jasmonate-stimulated anthocyanin production. Unexpectedly, melatonin could not repress the jasmonate-triggered JAZ protein degradation that is a key event for relaying jasmonate signaling. The expression of jasmonate-induced marker genes or other jasmonate-related phenotypes were not discernibly changed in the presence of melatonin. These results indicate that the antagonization of jasmonate-induced anthocyanin synthesis by melatonin does not occur through the abrogation of jasmonate signaling. Furthermore, we found that melatonin does not trigger anthocyanin catabolism. Finally, we supplied anthocyanin biosynthesis precursors to examine their roles in anthocyanin biosynthesis and found that melatonin most likely acts before the dihydrokaempferol production step. Our work illustrates that melatonin plays a negative role in the induction of anthocyanin biosynthesis and sheds new light on the role of melatonin in plant cell metabolism.